Added Nullity Annotations

app/src/main/java/com/kabouzeid/gramophone/adapter/AbsMultiSelectAdapter.java

@@ -16,6 +16,7 @@ import java.util.ArrayList;
  * @author Karim Abou Zeid (kabouzeid)
  */
 public abstract class AbsMultiSelectAdapter<VH extends RecyclerView.ViewHolder, I> extends RecyclerView.Adapter<VH> implements MaterialCab.Callback {
+    @Nullable
     private final CabHolder cabHolder;
     private MaterialCab cab;
     private ArrayList<I> checked;

app/src/main/java/com/kabouzeid/gramophone/adapter/AlbumAdapter.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.adapter;
 import android.annotation.TargetApi;
 import android.graphics.Bitmap;
 import android.os.Build;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -54,10 +55,12 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
     public static final String TAG = AlbumAdapter.class.getSimpleName();
     private static final int FADE_IN_TIME = 500;
 
+    @NonNull
     private final AppCompatActivity activity;
     private boolean usePalette;
     private List<Album> dataSet;
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_grid_album, parent, false);
@@ -65,7 +68,7 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         final Album album = dataSet.get(position);
 
         resetColors(holder.title, holder.artist, holder.footer);
@@ -114,7 +117,7 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Album> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Album> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_disk:
                 DeleteSongsDialog.create(getSongList(selection)).show(activity.getSupportFragmentManager(), "DELETE_SONGS");
@@ -128,7 +131,8 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
         }
     }
 
-    private ArrayList<Song> getSongList(List<Album> albums) {
+    @NonNull
+    private ArrayList<Song> getSongList(@NonNull List<Album> albums) {
         final ArrayList<Song> songs = new ArrayList<>();
         for (Album album : albums) {
             songs.addAll(AlbumSongLoader.getAlbumSongList(activity, album.id));
@@ -137,14 +141,19 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final ImageView albumArt;
+        @NonNull
         final TextView title;
+        @NonNull
         final TextView artist;
         final View footer;
+        @NonNull
         final ImageView checkMark;
+        @NonNull
         final View view;
 
-        public ViewHolder(View itemView) {
+        public ViewHolder(@NonNull View itemView) {
             super(itemView);
             view = itemView;
             albumArt = (ImageView) itemView.findViewById(R.id.album_art);
@@ -161,7 +170,7 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
 
                     @TargetApi(Build.VERSION_CODES.LOLLIPOP)
                     @Override
-                    public boolean onTouch(View view, MotionEvent motionEvent) {
+                    public boolean onTouch(@NonNull View view, @NonNull MotionEvent motionEvent) {
                         ((FrameLayout) view.findViewById(R.id.content)).getForeground().setHotspot(motionEvent.getX(), motionEvent.getY());
                         return false;
                     }
@@ -191,7 +200,7 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
         }
     }
 
-    public AlbumAdapter(AppCompatActivity activity, @Nullable CabHolder cabHolder) {
+    public AlbumAdapter(@NonNull AppCompatActivity activity, @Nullable CabHolder cabHolder) {
         super(activity, cabHolder, R.menu.menu_media_selection);
         this.activity = activity;
         usePalette = PreferenceUtils.getInstance(activity).coloredAlbumFooters();
@@ -208,13 +217,13 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
         dataSet = AlbumLoader.getAllAlbums(activity);
     }
 
-    private void applyPalette(Bitmap bitmap, final TextView title, final TextView artist, final View footer) {
+    private void applyPalette(@Nullable Bitmap bitmap, @NonNull final TextView title, @NonNull final TextView artist, @NonNull final View footer) {
         if (bitmap != null) {
             Palette.from(bitmap)
                     .resizeBitmapSize(100)
                     .generate(new Palette.PaletteAsyncListener() {
                         @Override
-                        public void onGenerated(Palette palette) {
+                        public void onGenerated(@NonNull Palette palette) {
                             final Palette.Swatch vibrantSwatch = palette.getVibrantSwatch();
                             if (vibrantSwatch != null) {
                                 title.setTextColor(Util.getOpaqueColor(vibrantSwatch.getTitleTextColor()));
@@ -230,14 +239,14 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
         }
     }
 
-    private void paletteBlackAndWhite(final TextView title, final TextView artist, final View footer) {
+    private void paletteBlackAndWhite(@NonNull final TextView title, @NonNull final TextView artist, final View footer) {
         title.setTextColor(Util.getOpaqueColor(DialogUtils.resolveColor(activity, R.attr.title_text_color)));
         artist.setTextColor(Util.getOpaqueColor(DialogUtils.resolveColor(activity, R.attr.caption_text_color)));
         int defaultBarColor = DialogUtils.resolveColor(activity, R.attr.default_bar_color);
         ViewUtil.animateViewColor(footer, defaultBarColor, defaultBarColor);
     }
 
-    private void resetColors(final TextView title, final TextView artist, final View footer) {
+    private void resetColors(@NonNull final TextView title, @NonNull final TextView artist, @NonNull final View footer) {
         title.setTextColor(DialogUtils.resolveColor(activity, R.attr.title_text_color));
         artist.setTextColor(DialogUtils.resolveColor(activity, R.attr.caption_text_color));
         int defaultBarColor = DialogUtils.resolveColor(activity, R.attr.default_bar_color);
@@ -257,7 +266,7 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.ALBUMS_CHANGED:
             case DataBaseChangedEvent.DATABASE_CHANGED:
@@ -268,7 +277,7 @@ public class AlbumAdapter extends AbsMultiSelectAdapter<AlbumAdapter.ViewHolder,
     }
 
     @Subscribe
-    public void onUIChangeEvent(UIPreferenceChangedEvent event) {
+    public void onUIChangeEvent(@NonNull UIPreferenceChangedEvent event) {
         switch (event.getAction()) {
             case UIPreferenceChangedEvent.ALBUM_OVERVIEW_PALETTE_CHANGED:
                 usePalette = (boolean) event.getValue();

app/src/main/java/com/kabouzeid/gramophone/adapter/ArtistAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -43,11 +44,13 @@ import retrofit.client.Response;
  * @author Karim Abou Zeid (kabouzeid)
  */
 public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolder, Artist> {
+    @NonNull
     protected final AppCompatActivity activity;
     protected List<Artist> dataSet;
+    @NonNull
     protected final LastFMRestClient lastFMRestClient;
 
-    public ArtistAdapter(AppCompatActivity activity, @Nullable CabHolder cabHolder) {
+    public ArtistAdapter(@NonNull AppCompatActivity activity, @Nullable CabHolder cabHolder) {
         super(activity, cabHolder, R.menu.menu_media_selection);
         this.activity = activity;
         lastFMRestClient = new LastFMRestClient(activity);
@@ -64,6 +67,7 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
         dataSet = ArtistLoader.getAllArtists(activity);
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_list_artist, parent, false);
@@ -71,7 +75,7 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         final Artist artist = dataSet.get(position);
 
         holder.artistName.setText(artist.name);
@@ -85,7 +89,7 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
 
         lastFMRestClient.getApiService().getArtistInfo(artist.name, null, new Callback<ArtistInfo>() {
             @Override
-            public void success(ArtistInfo artistInfo, Response response) {
+            public void success(@NonNull ArtistInfo artistInfo, Response response) {
                 if (artistInfo.getArtist() != null) {
                     int thumbnailIndex = 0;
                     List<Image> images = artistInfo.getArtist().getImage();
@@ -127,7 +131,7 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Artist> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Artist> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_disk:
                 DeleteSongsDialog.create(getSongList(selection)).show(activity.getSupportFragmentManager(), "DELETE_SONGS");
@@ -141,7 +145,8 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
         }
     }
 
-    private ArrayList<Song> getSongList(List<Artist> artists) {
+    @NonNull
+    private ArrayList<Song> getSongList(@NonNull List<Artist> artists) {
         final ArrayList<Song> songs = new ArrayList<>();
         for (Artist artist : artists) {
             songs.addAll(ArtistSongLoader.getArtistSongList(activity, artist.id));
@@ -150,12 +155,16 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final TextView artistName;
+        @NonNull
         final TextView artistInfo;
+        @NonNull
         final ImageView artistImage;
+        @NonNull
         final View view;
 
-        public ViewHolder(View itemView) {
+        public ViewHolder(@NonNull View itemView) {
             super(itemView);
             view = itemView;
             artistName = (TextView) itemView.findViewById(R.id.artist_name);
@@ -200,7 +209,7 @@ public class ArtistAdapter extends AbsMultiSelectAdapter<ArtistAdapter.ViewHolde
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.ARTISTS_CHANGED:
             case DataBaseChangedEvent.DATABASE_CHANGED:

app/src/main/java/com/kabouzeid/gramophone/adapter/ArtistAlbumAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -38,11 +39,12 @@ public class ArtistAlbumAdapter extends AbsMultiSelectAdapter<ArtistAlbumAdapter
     private static final int TYPE_MIDDLE = 2;
     private static final int TYPE_LAST = 3;
 
+    @NonNull
     private final AppCompatActivity activity;
     private ArrayList<Album> dataSet;
     private final int listMargin;
 
-    public ArtistAlbumAdapter(AppCompatActivity activity, ArrayList<Album> objects, @Nullable CabHolder cabHolder) {
+    public ArtistAlbumAdapter(@NonNull AppCompatActivity activity, ArrayList<Album> objects, @Nullable CabHolder cabHolder) {
         super(activity, cabHolder, R.menu.menu_media_selection);
         this.activity = activity;
         dataSet = objects;
@@ -60,6 +62,7 @@ public class ArtistAlbumAdapter extends AbsMultiSelectAdapter<ArtistAlbumAdapter
         notifyDataSetChanged();
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_grid_artist_album, parent, false);
@@ -73,7 +76,7 @@ public class ArtistAlbumAdapter extends AbsMultiSelectAdapter<ArtistAlbumAdapter
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         final Album album = dataSet.get(position);
 
         ImageLoader.getInstance().displayImage(
@@ -111,7 +114,7 @@ public class ArtistAlbumAdapter extends AbsMultiSelectAdapter<ArtistAlbumAdapter
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Album> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Album> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_disk:
                 DeleteSongsDialog.create(getSongList(selection)).show(activity.getSupportFragmentManager(), "DELETE_SONGS");
@@ -125,7 +128,8 @@ public class ArtistAlbumAdapter extends AbsMultiSelectAdapter<ArtistAlbumAdapter
         }
     }
 
-    private ArrayList<Song> getSongList(List<Album> albums) {
+    @NonNull
+    private ArrayList<Song> getSongList(@NonNull List<Album> albums) {
         final ArrayList<Song> songs = new ArrayList<>();
         for (Album album : albums) {
             songs.addAll(AlbumSongLoader.getAlbumSongList(activity, album.id));
@@ -134,12 +138,16 @@ public class ArtistAlbumAdapter extends AbsMultiSelectAdapter<ArtistAlbumAdapter
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final ImageView albumArt;
+        @NonNull
         final TextView title;
+        @NonNull
         final TextView year;
+        @NonNull
         final View view;
 
-        public ViewHolder(View itemView) {
+        public ViewHolder(@NonNull View itemView) {
             super(itemView);
             view = itemView;
             albumArt = (ImageView) itemView.findViewById(R.id.album_art);

app/src/main/java/com/kabouzeid/gramophone/adapter/PagerAdapter.java

@@ -2,6 +2,7 @@ package com.kabouzeid.gramophone.adapter;
 
 import android.content.Context;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentPagerAdapter;
@@ -25,13 +26,15 @@ public class PagerAdapter extends FragmentPagerAdapter {
 
     private final List<Holder> mHolderList = new ArrayList<>();
 
+    @NonNull
     private final Context mContext;
 
     private int mCurrentPage;
 
+    @NonNull
     private final String[] titles;
 
-    public PagerAdapter(final Context context, final FragmentManager fragmentManager) {
+    public PagerAdapter(@NonNull final Context context, final FragmentManager fragmentManager) {
         super(fragmentManager);
         mContext = context;
         titles = new String[]{
@@ -43,7 +46,7 @@ public class PagerAdapter extends FragmentPagerAdapter {
     }
 
     @SuppressWarnings("synthetic-access")
-    public void add(final Class<? extends Fragment> className, final Bundle params) {
+    public void add(@NonNull final Class<? extends Fragment> className, final Bundle params) {
         final Holder mHolder = new Holder();
         mHolder.mClassName = className.getName();
         mHolder.mParams = params;
@@ -61,8 +64,9 @@ public class PagerAdapter extends FragmentPagerAdapter {
         return getItem(position);
     }
 
+    @NonNull
     @Override
-    public Object instantiateItem(final ViewGroup container, final int position) {
+    public Object instantiateItem(@NonNull final ViewGroup container, final int position) {
         final Fragment mFragment = (Fragment) super.instantiateItem(container, position);
         final WeakReference<Fragment> mWeakFragment = mFragmentArray.get(position);
         if (mWeakFragment != null) {
@@ -93,6 +97,7 @@ public class PagerAdapter extends FragmentPagerAdapter {
         return mHolderList.size();
     }
 
+    @NonNull
     @Override
     public CharSequence getPageTitle(final int position) {
         return titles[position]

app/src/main/java/com/kabouzeid/gramophone/adapter/PlayingQueueAdapter.java

@@ -1,5 +1,7 @@
 package com.kabouzeid.gramophone.adapter;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 import android.view.LayoutInflater;
 import android.view.MenuItem;
@@ -24,15 +26,17 @@ import java.util.ArrayList;
  */
 public class PlayingQueueAdapter extends ArrayAdapter<Song> {
 
+    @NonNull
     private final AppCompatActivity activity;
 
-    public PlayingQueueAdapter(AppCompatActivity activity, ArrayList<Song> playList) {
+    public PlayingQueueAdapter(@NonNull AppCompatActivity activity, @NonNull ArrayList<Song> playList) {
         super(activity, R.layout.item_list_playlist_song, playList);
         this.activity = activity;
     }
 
+    @Nullable
     @Override
-    public View getView(final int position, View convertView, ViewGroup parent) {
+    public View getView(final int position, @Nullable View convertView, ViewGroup parent) {
         final Song song = getItem(position);
         if (convertView == null) {
             convertView = LayoutInflater.from(activity).inflate(R.layout.item_list_playlist_song, parent, false);
@@ -56,7 +60,7 @@ public class PlayingQueueAdapter extends ArrayAdapter<Song> {
                 popupMenu.inflate(R.menu.menu_item_playing_queue_song);
                 popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                     @Override
-                    public boolean onMenuItemClick(MenuItem item) {
+                    public boolean onMenuItemClick(@NonNull MenuItem item) {
                         if (item.getItemId() == R.id.action_remove_from_playing_queue) {
                             MusicPlayerRemote.removeFromQueue(position);
                             notifyDataSetChanged();

app/src/main/java/com/kabouzeid/gramophone/adapter/PlaylistAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -72,6 +73,7 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
         dataSet.addAll(PlaylistLoader.getAllPlaylists(activity));
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         int layoutRes = viewType == VIEW_TYPE_DEFAULT ? R.layout.item_list_playlist : R.layout.item_list_smart_playlist;
@@ -80,7 +82,7 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
     }
 
     @Override
-    public void onBindViewHolder(ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
         final Playlist playlist = dataSet.get(position);
         holder.playlistName.setText(playlist.name);
         holder.view.setActivated(isChecked(playlist));
@@ -110,7 +112,7 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Playlist> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Playlist> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_playlist:
                 for (int i = 0; i < selection.size(); i++) {
@@ -135,7 +137,8 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
         }
     }
 
-    private ArrayList<Song> getSongList(List<Playlist> playlists) {
+    @NonNull
+    private ArrayList<Song> getSongList(@NonNull List<Playlist> playlists) {
         final ArrayList<Song> songs = new ArrayList<>();
         for (Playlist playlist : playlists) {
             if (playlist instanceof AbsSmartPlaylist) {
@@ -156,7 +159,7 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
         ImageView icon;
         View view;
 
-        public ViewHolder(View itemView) {
+        public ViewHolder(@NonNull View itemView) {
             super(itemView);
             ButterKnife.inject(this, itemView);
             view = itemView;
@@ -169,7 +172,7 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
                     popupMenu.inflate(getItemViewType() == VIEW_TYPE_SMART ? R.menu.menu_item_smart_playlist : R.menu.menu_item_playlist);
                     popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                         @Override
-                        public boolean onMenuItemClick(MenuItem item) {
+                        public boolean onMenuItemClick(@NonNull MenuItem item) {
                             if (item.getItemId() == R.id.action_clear_playlist) {
                                 Playlist playlist = dataSet.get(getAdapterPosition());
                                 if (playlist instanceof AbsSmartPlaylist) {
@@ -219,7 +222,7 @@ public class PlaylistAdapter extends AbsMultiSelectAdapter<PlaylistAdapter.ViewH
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.PLAYLISTS_CHANGED:
             case DataBaseChangedEvent.DATABASE_CHANGED:

app/src/main/java/com/kabouzeid/gramophone/adapter/SearchAdapter.java

@@ -1,5 +1,7 @@
 package com.kabouzeid.gramophone.adapter;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.RecyclerView;
@@ -48,18 +50,21 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
     private static final int ARTIST = 2;
     private static final int SONG = 3;
 
+    @NonNull
     private final AppCompatActivity activity;
+    @NonNull
     private List results = Collections.emptyList();
     private String query;
+    @NonNull
     private final LastFMRestClient lastFMRestClient;
 
-    public SearchAdapter(AppCompatActivity activity) {
+    public SearchAdapter(@NonNull AppCompatActivity activity) {
         this.activity = activity;
         lastFMRestClient = new LastFMRestClient(activity);
     }
 
     @SuppressWarnings("unchecked")
-    public void search(String query) {
+    public void search(@NonNull String query) {
         this.query = query;
         results = new ArrayList();
         if (!query.trim().equals("")) {
@@ -92,6 +97,7 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
         return HEADER;
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         if (viewType == ALBUM)
@@ -104,7 +110,7 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         switch (getItemViewType(position)) {
             case ALBUM:
                 final Album album = (Album) results.get(position);
@@ -130,7 +136,7 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
                 }
                 lastFMRestClient.getApiService().getArtistInfo(artist.name, null, new Callback<ArtistInfo>() {
                     @Override
-                    public void success(ArtistInfo artistInfo, Response response) {
+                    public void success(@NonNull ArtistInfo artistInfo, Response response) {
                         if (artistInfo.getArtist() != null) {
                             int thumbnailIndex = 0;
                             List<Image> images = artistInfo.getArtist().getImage();
@@ -177,12 +183,15 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
+        @Nullable
         private final ImageView image;
+        @NonNull
         public final TextView title;
+        @Nullable
         public final TextView subTitle;
         private final int viewType;
 
-        public ViewHolder(View itemView, int viewType) {
+        public ViewHolder(@NonNull View itemView, int viewType) {
             super(itemView);
             itemView.setOnClickListener(this);
             this.viewType = viewType;
@@ -208,7 +217,7 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
                             popupMenu.inflate(R.menu.menu_item_song);
                             popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                                 @Override
-                                public boolean onMenuItemClick(MenuItem menuItem) {
+                                public boolean onMenuItemClick(@NonNull MenuItem menuItem) {
                                     return MenuItemClickHelper.handleSongMenuClick(activity, (Song) results.get(getAdapterPosition()), menuItem);
                                 }
                             });
@@ -269,7 +278,7 @@ public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.ViewHolder
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.ALBUMS_CHANGED:
             case DataBaseChangedEvent.DATABASE_CHANGED:

app/src/main/java/com/kabouzeid/gramophone/adapter/songadapter/AlbumSongAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter.songadapter;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.RecyclerView;
@@ -49,6 +50,7 @@ public class AlbumSongAdapter extends AbsMultiSelectAdapter<AlbumSongAdapter.Vie
         notifyDataSetChanged();
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_list_album_song, parent, false);
@@ -56,7 +58,7 @@ public class AlbumSongAdapter extends AbsMultiSelectAdapter<AlbumSongAdapter.Vie
     }
 
     @Override
-    public void onBindViewHolder(ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
         final Song song = dataSet.get(position);
 
         final int trackNumber = MusicUtil.getFixedTrackNumber(song.trackNumber);
@@ -78,7 +80,7 @@ public class AlbumSongAdapter extends AbsMultiSelectAdapter<AlbumSongAdapter.Vie
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Song> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Song> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_disk:
                 DeleteSongsDialog.create(selection).show(activity.getSupportFragmentManager(), "DELETE_SONGS");
@@ -93,13 +95,18 @@ public class AlbumSongAdapter extends AbsMultiSelectAdapter<AlbumSongAdapter.Vie
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final TextView songTitle;
+        @NonNull
         final TextView trackNumber;
+        @NonNull
         final TextView artistName;
+        @NonNull
         final ImageView overflowButton;
+        @NonNull
         final View view;
 
-        public ViewHolder(View itemView) {
+        public ViewHolder(@NonNull View itemView) {
             super(itemView);
             view = itemView;
             songTitle = (TextView) itemView.findViewById(R.id.song_title);
@@ -115,7 +122,7 @@ public class AlbumSongAdapter extends AbsMultiSelectAdapter<AlbumSongAdapter.Vie
                     popupMenu.inflate(R.menu.menu_item_song);
                     popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                         @Override
-                        public boolean onMenuItemClick(MenuItem item) {
+                        public boolean onMenuItemClick(@NonNull MenuItem item) {
                             return MenuItemClickHelper.handleSongMenuClick(activity, dataSet.get(getAdapterPosition()), item);
                         }
                     });

app/src/main/java/com/kabouzeid/gramophone/adapter/songadapter/ArtistSongAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter.songadapter;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -34,14 +35,16 @@ import java.util.ArrayList;
  */
 public class ArtistSongAdapter extends ArrayAdapter<Song> implements MaterialCab.Callback {
 
+    @Nullable
     private final CabHolder cabHolder;
     private MaterialCab cab;
     private ArrayList<Song> dataSet;
     private ArrayList<Song> checked;
 
+    @NonNull
     private final AppCompatActivity activity;
 
-    public ArtistSongAdapter(AppCompatActivity activity, ArrayList<Song> songs, @Nullable CabHolder cabHolder) {
+    public ArtistSongAdapter(@NonNull AppCompatActivity activity, @NonNull ArrayList<Song> songs, @Nullable CabHolder cabHolder) {
         super(activity, R.layout.item_list_song, songs);
         this.activity = activity;
         this.cabHolder = cabHolder;
@@ -55,8 +58,9 @@ public class ArtistSongAdapter extends ArrayAdapter<Song> implements MaterialCab
         addAll(dataSet);
     }
 
+    @Nullable
     @Override
-    public View getView(final int position, View convertView, ViewGroup parent) {
+    public View getView(final int position, @Nullable View convertView, ViewGroup parent) {
         final Song song = getItem(position);
         if (convertView == null) {
             convertView = LayoutInflater.from(getContext()).inflate(R.layout.item_list_artist_song, parent, false);
@@ -87,7 +91,7 @@ public class ArtistSongAdapter extends ArrayAdapter<Song> implements MaterialCab
                 popupMenu.inflate(R.menu.menu_item_song);
                 popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                     @Override
-                    public boolean onMenuItemClick(MenuItem item) {
+                    public boolean onMenuItemClick(@NonNull MenuItem item) {
                         switch (item.getItemId()) {
                             case R.id.action_go_to_album:
                                 Pair[] albumPairs = new Pair[]{
@@ -127,7 +131,7 @@ public class ArtistSongAdapter extends ArrayAdapter<Song> implements MaterialCab
         return convertView;
     }
 
-    private void onMultipleItemAction(MenuItem menuItem, ArrayList<Song> selection) {
+    private void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Song> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_disk:
                 DeleteSongsDialog.create(selection).show(activity.getSupportFragmentManager(), "DELETE_SONGS");
@@ -182,7 +186,7 @@ public class ArtistSongAdapter extends ArrayAdapter<Song> implements MaterialCab
     }
 
     @Override
-    public boolean onCabItemClicked(MenuItem menuItem) {
+    public boolean onCabItemClicked(@NonNull MenuItem menuItem) {
         onMultipleItemAction(menuItem, new ArrayList<>(checked));
         cab.finish();
         uncheckAll();

app/src/main/java/com/kabouzeid/gramophone/adapter/songadapter/PlaylistSongAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter.songadapter;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -39,11 +40,12 @@ import java.util.List;
 public class PlaylistSongAdapter extends AbsPlaylistSongAdapter<PlaylistSongAdapter.ViewHolder, PlaylistSong> {
 
     public static final String TAG = PlaylistSongAdapter.class.getSimpleName();
+    @NonNull
     protected final AppCompatActivity activity;
     protected ArrayList<PlaylistSong> dataSet;
     private Playlist playlist;
 
-    public PlaylistSongAdapter(AppCompatActivity activity, Playlist playlist, @Nullable CabHolder cabHolder) {
+    public PlaylistSongAdapter(@NonNull AppCompatActivity activity, @NonNull Playlist playlist, @Nullable CabHolder cabHolder) {
         super(activity, cabHolder, R.menu.menu_playlists_songs_selection);
         this.activity = activity;
         this.playlist = playlist;
@@ -67,6 +69,7 @@ public class PlaylistSongAdapter extends AbsPlaylistSongAdapter<PlaylistSongAdap
         return dataSet;
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_list_song, parent, false);
@@ -74,7 +77,7 @@ public class PlaylistSongAdapter extends AbsPlaylistSongAdapter<PlaylistSongAdap
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         final PlaylistSong song = dataSet.get(position);
 
         holder.itemView.setActivated(isChecked(song));
@@ -102,7 +105,7 @@ public class PlaylistSongAdapter extends AbsPlaylistSongAdapter<PlaylistSongAdap
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<PlaylistSong> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, ArrayList<PlaylistSong> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_playlist:
                 RemoveFromPlaylistDialog.create(selection).show(activity.getSupportFragmentManager(), "ADD_PLAYLIST");
@@ -129,12 +132,16 @@ public class PlaylistSongAdapter extends AbsPlaylistSongAdapter<PlaylistSongAdap
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final TextView songTitle;
+        @NonNull
         final TextView songInfo;
+        @NonNull
         final ImageView overflowButton;
+        @NonNull
         final ImageView albumArt;
 
-        public ViewHolder(View itemView, final int songMenu) {
+        public ViewHolder(@NonNull View itemView, final int songMenu) {
             super(itemView);
             songTitle = (TextView) itemView.findViewById(R.id.song_title);
             songInfo = (TextView) itemView.findViewById(R.id.song_info);
@@ -149,7 +156,7 @@ public class PlaylistSongAdapter extends AbsPlaylistSongAdapter<PlaylistSongAdap
                     popupMenu.inflate(songMenu);
                     popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                         @Override
-                        public boolean onMenuItemClick(MenuItem item) {
+                        public boolean onMenuItemClick(@NonNull MenuItem item) {
                             switch (item.getItemId()) {
                                 case R.id.action_delete_from_playlist:
                                     RemoveFromPlaylistDialog.create(dataSet.get(getAdapterPosition())).show(activity.getSupportFragmentManager(), "ADD_PLAYLIST");

app/src/main/java/com/kabouzeid/gramophone/adapter/songadapter/SongAdapter.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.adapter.songadapter;
 
 import android.graphics.Typeface;
+import android.support.annotation.NonNull;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.RecyclerView;
@@ -63,6 +64,7 @@ public class SongAdapter extends AbsMultiSelectAdapter<SongAdapter.ViewHolder, S
         dataSet = SongLoader.getAllSongs(activity);
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_list_song, parent, false);
@@ -75,7 +77,7 @@ public class SongAdapter extends AbsMultiSelectAdapter<SongAdapter.ViewHolder, S
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         if (getItemViewType(position) == SONG) {
             final Song song = dataSet.get(position - 1);
 
@@ -118,7 +120,7 @@ public class SongAdapter extends AbsMultiSelectAdapter<SongAdapter.ViewHolder, S
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Song> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Song> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_delete_from_disk:
                 DeleteSongsDialog.create(selection).show(activity.getSupportFragmentManager(), "DELETE_SONGS");
@@ -133,15 +135,20 @@ public class SongAdapter extends AbsMultiSelectAdapter<SongAdapter.ViewHolder, S
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final TextView songTitle;
+        @NonNull
         final TextView songInfo;
+        @NonNull
         final ImageView overflowButton;
+        @NonNull
         final ImageView albumArt;
         final View separator;
         final View short_separator;
+        @NonNull
         final View view;
 
-        public ViewHolder(View itemView) {
+        public ViewHolder(@NonNull View itemView) {
             super(itemView);
             view = itemView;
             songTitle = (TextView) itemView.findViewById(R.id.song_title);
@@ -159,7 +166,7 @@ public class SongAdapter extends AbsMultiSelectAdapter<SongAdapter.ViewHolder, S
                     popupMenu.inflate(R.menu.menu_item_song);
                     popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                         @Override
-                        public boolean onMenuItemClick(MenuItem item) {
+                        public boolean onMenuItemClick(@NonNull MenuItem item) {
                             final int position = getAdapterPosition() - 1;
                             switch (item.getItemId()) {
                                 case R.id.action_go_to_album:
@@ -212,7 +219,7 @@ public class SongAdapter extends AbsMultiSelectAdapter<SongAdapter.ViewHolder, S
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.SONGS_CHANGED:
             case DataBaseChangedEvent.DATABASE_CHANGED:

app/src/main/java/com/kabouzeid/gramophone/adapter/songadapter/smartplaylist/SmartPlaylistSongAdapter.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.adapter.songadapter.smartplaylist;
 
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
@@ -51,7 +52,7 @@ public class SmartPlaylistSongAdapter extends AbsPlaylistSongAdapter<SmartPlayli
         return dataSet.get(position).id;
     }
 
-    public SmartPlaylistSongAdapter(AppCompatActivity activity, AbsSmartPlaylist playlist, @Nullable CabHolder cabHolder) {
+    public SmartPlaylistSongAdapter(AppCompatActivity activity, @NonNull AbsSmartPlaylist playlist, @Nullable CabHolder cabHolder) {
         super(activity, cabHolder, R.menu.menu_cannot_delete_single_songs_playlist_songs_selection);
         this.activity = activity;
         this.playlist = playlist;
@@ -63,6 +64,7 @@ public class SmartPlaylistSongAdapter extends AbsPlaylistSongAdapter<SmartPlayli
         return dataSet;
     }
 
+    @NonNull
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View view = LayoutInflater.from(activity).inflate(R.layout.item_list_song, parent, false);
@@ -70,7 +72,7 @@ public class SmartPlaylistSongAdapter extends AbsPlaylistSongAdapter<SmartPlayli
     }
 
     @Override
-    public void onBindViewHolder(final ViewHolder holder, int position) {
+    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
         final Song song = dataSet.get(position);
 
         holder.itemView.setActivated(isChecked(song));
@@ -98,7 +100,7 @@ public class SmartPlaylistSongAdapter extends AbsPlaylistSongAdapter<SmartPlayli
     }
 
     @Override
-    protected void onMultipleItemAction(MenuItem menuItem, ArrayList<Song> selection) {
+    protected void onMultipleItemAction(@NonNull MenuItem menuItem, @NonNull ArrayList<Song> selection) {
         switch (menuItem.getItemId()) {
             case R.id.action_add_to_playlist:
                 onAddToPlaylist(selection);
@@ -113,17 +115,21 @@ public class SmartPlaylistSongAdapter extends AbsPlaylistSongAdapter<SmartPlayli
         AddToPlaylistDialog.create(songs).show(activity.getSupportFragmentManager(), "ADD_PLAYLIST");
     }
 
-    protected void onAddToCurrentPlaying(ArrayList<Song> songs) {
+    protected void onAddToCurrentPlaying(@NonNull ArrayList<Song> songs) {
         MusicPlayerRemote.enqueue(songs);
     }
 
     public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener {
+        @NonNull
         final TextView songTitle;
+        @NonNull
         final TextView songInfo;
+        @NonNull
         final ImageView overflowButton;
+        @NonNull
         final ImageView albumArt;
 
-        public ViewHolder(View itemView, final int songMenu) {
+        public ViewHolder(@NonNull View itemView, final int songMenu) {
             super(itemView);
             songTitle = (TextView) itemView.findViewById(R.id.song_title);
             songInfo = (TextView) itemView.findViewById(R.id.song_info);
@@ -138,7 +144,7 @@ public class SmartPlaylistSongAdapter extends AbsPlaylistSongAdapter<SmartPlayli
                     popupMenu.inflate(songMenu);
                     popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                         @Override
-                        public boolean onMenuItemClick(MenuItem item) {
+                        public boolean onMenuItemClick(@NonNull MenuItem item) {
                             switch (item.getItemId()) {
                                 case R.id.action_go_to_album:
                                     Pair[] albumPairs = new Pair[]{

app/src/main/java/com/kabouzeid/gramophone/appwidget/WidgetMedium.java

@@ -7,6 +7,8 @@ import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
 import android.graphics.Bitmap;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.view.View;
 import android.widget.RemoteViews;
 
@@ -28,14 +30,14 @@ public class WidgetMedium extends AppWidgetProvider {
     private static String currentAlbumArtUri;
 
     @Override
-    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
+    public void onUpdate(@NonNull Context context, @NonNull AppWidgetManager appWidgetManager, @NonNull int[] appWidgetIds) {
         updateWidgets(context, MusicPlayerRemote.getCurrentSong(), MusicPlayerRemote.isPlaying());
         for (int widgetId : appWidgetIds) {
             appWidgetManager.updateAppWidget(widgetId, widgetLayout);
         }
     }
 
-    public static void updateWidgets(final Context context, final Song song, boolean isPlaying) {
+    public static void updateWidgets(@NonNull final Context context, @NonNull final Song song, boolean isPlaying) {
         if (song.id == -1) return;
         widgetLayout = new RemoteViews(context.getPackageName(), R.layout.widget_medium);
         linkButtons(context, widgetLayout);
@@ -45,7 +47,7 @@ public class WidgetMedium extends AppWidgetProvider {
         loadAlbumArt(context, song);
     }
 
-    public static void updateWidgetsPlayState(final Context context, boolean isPlaying) {
+    public static void updateWidgetsPlayState(@NonNull final Context context, boolean isPlaying) {
         if (widgetLayout == null)
             widgetLayout = new RemoteViews(context.getPackageName(), R.layout.widget_medium);
         int playPauseRes = isPlaying ? R.drawable.ic_pause_black_36dp : R.drawable.ic_play_arrow_black_36dp;
@@ -53,7 +55,7 @@ public class WidgetMedium extends AppWidgetProvider {
         updateWidgets(context);
     }
 
-    private static void updateWidgets(final Context context) {
+    private static void updateWidgets(@NonNull final Context context) {
         AppWidgetManager man = AppWidgetManager.getInstance(context);
         int[] ids = man.getAppWidgetIds(
                 new ComponentName(context, WidgetMedium.class));
@@ -62,12 +64,12 @@ public class WidgetMedium extends AppWidgetProvider {
         }
     }
 
-    private static void loadAlbumArt(final Context context, final Song song) {
+    private static void loadAlbumArt(@NonNull final Context context, @Nullable final Song song) {
         if (song != null) {
             currentAlbumArtUri = MusicUtil.getSongImageLoaderString(song);
             ImageLoader.getInstance().displayImage(currentAlbumArtUri, new NonViewAware(new ImageSize(-1, -1), ViewScaleType.CROP), new SimpleImageLoadingListener() {
                 @Override
-                public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
+                public void onLoadingComplete(String imageUri, View view, @Nullable Bitmap loadedImage) {
                     if (currentAlbumArtUri.equals(imageUri)) {
                         if (loadedImage != null) {
                             // The RemoteViews might wants to recycle the bitmaps thrown at it, so we need
@@ -94,7 +96,7 @@ public class WidgetMedium extends AppWidgetProvider {
         }
     }
 
-    private static void setAlbumArt(final Context context, final Bitmap albumArt) {
+    private static void setAlbumArt(@NonNull final Context context, @Nullable final Bitmap albumArt) {
         if (albumArt != null) {
             widgetLayout.setImageViewBitmap(R.id.album_art, albumArt);
         } else {
@@ -103,7 +105,7 @@ public class WidgetMedium extends AppWidgetProvider {
         updateWidgets(context);
     }
 
-    private static void linkButtons(final Context context, final RemoteViews views) {
+    private static void linkButtons(@NonNull final Context context, @NonNull final RemoteViews views) {
         views.setOnClickPendingIntent(R.id.album_art, retrievePlaybackActions(context, 0));
         views.setOnClickPendingIntent(R.id.media_titles, retrievePlaybackActions(context, 0));
         views.setOnClickPendingIntent(R.id.button_toggle_play_pause, retrievePlaybackActions(context, 1));
@@ -111,7 +113,7 @@ public class WidgetMedium extends AppWidgetProvider {
         views.setOnClickPendingIntent(R.id.button_prev, retrievePlaybackActions(context, 3));
     }
 
-    private static PendingIntent retrievePlaybackActions(final Context context, final int which) {
+    private static PendingIntent retrievePlaybackActions(@NonNull final Context context, final int which) {
         Intent action;
         PendingIntent pendingIntent;
         final ComponentName serviceName = new ComponentName(context, MusicService.class);

app/src/main/java/com/kabouzeid/gramophone/dialogs/AboutDialog.java

@@ -31,7 +31,7 @@ public class AboutDialog extends DialogFragment {
                 .build();
     }
 
-    private static String getCurrentVersionName(final Context context) {
+    private static String getCurrentVersionName(@NonNull final Context context) {
         String versionName;
         try {
             versionName = context.getPackageManager().getPackageInfo(context.getPackageName(), 0).versionName;

app/src/main/java/com/kabouzeid/gramophone/dialogs/AddToPlaylistDialog.java

@@ -21,12 +21,14 @@ import java.util.List;
  */
 public class AddToPlaylistDialog extends DialogFragment {
 
+    @NonNull
     public static AddToPlaylistDialog create(Song song) {
         ArrayList<Song> list = new ArrayList<>();
         list.add(song);
         return create(list);
     }
 
+    @NonNull
     public static AddToPlaylistDialog create(ArrayList<Song> songs) {
         AddToPlaylistDialog dialog = new AddToPlaylistDialog();
         Bundle args = new Bundle();
@@ -49,7 +51,7 @@ public class AddToPlaylistDialog extends DialogFragment {
                 .items(playlistNames)
                 .itemsCallback(new MaterialDialog.ListCallback() {
                     @Override
-                    public void onSelection(MaterialDialog materialDialog, View view, int i, CharSequence charSequence) {
+                    public void onSelection(@NonNull MaterialDialog materialDialog, View view, int i, CharSequence charSequence) {
                         //noinspection unchecked
                         final ArrayList<Song> songs = (ArrayList<Song>) getArguments().getSerializable("songs");
                         if (i == 0) {

app/src/main/java/com/kabouzeid/gramophone/dialogs/ClearSmartPlaylistDialog.java

@@ -15,6 +15,7 @@ import com.kabouzeid.gramophone.model.smartplaylist.AbsSmartPlaylist;
  */
 public class ClearSmartPlaylistDialog extends DialogFragment {
 
+    @NonNull
     public static ClearSmartPlaylistDialog create(AbsSmartPlaylist playlist) {
         ClearSmartPlaylistDialog dialog = new ClearSmartPlaylistDialog();
         Bundle args = new Bundle();

app/src/main/java/com/kabouzeid/gramophone/dialogs/ColorChooserDialog.java

@@ -13,6 +13,8 @@ import android.graphics.drawable.StateListDrawable;
 import android.graphics.drawable.shapes.OvalShape;
 import android.os.Build;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.content.res.ResourcesCompat;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -31,6 +33,7 @@ public class ColorChooserDialog extends DialogFragment implements View.OnClickLi
 
     private ColorCallback mCallback;
     private int[] mColors;
+    @Nullable
     private GridView mGrid;
 
     @Override
@@ -40,7 +43,7 @@ public class ColorChooserDialog extends DialogFragment implements View.OnClickLi
     }
 
     @Override
-    public void onClick(View v) {
+    public void onClick(@NonNull View v) {
         if (v.getTag() != null) {
             final int index = (Integer) v.getTag();
             getArguments().putInt("preselect", mColors[index]);
@@ -128,8 +131,9 @@ public class ColorChooserDialog extends DialogFragment implements View.OnClickLi
             return position;
         }
 
+        @Nullable
         @Override
-        public View getView(int position, View convertView, ViewGroup parent) {
+        public View getView(int position, @Nullable View convertView, ViewGroup parent) {
             if (convertView == null)
                 convertView = LayoutInflater.from(getActivity()).inflate(R.layout.griditem_color_chooser, parent, false);
 
@@ -156,7 +160,7 @@ public class ColorChooserDialog extends DialogFragment implements View.OnClickLi
         }
 
         @Override
-        public void onClick(View v) {
+        public void onClick(@NonNull View v) {
             final int index = (Integer) v.getTag();
             getArguments().putInt("preselect", mColors[index]);
             invalidateGrid();
@@ -180,6 +184,7 @@ public class ColorChooserDialog extends DialogFragment implements View.OnClickLi
         return Color.argb(alpha, red, green, blue);
     }
 
+    @NonNull
     private static Drawable createSelector(int color) {
         ShapeDrawable darkerCircle = new ShapeDrawable(new OvalShape());
         darkerCircle.getPaint().setColor(translucentColor(shiftColorDown(color)));
@@ -188,7 +193,7 @@ public class ColorChooserDialog extends DialogFragment implements View.OnClickLi
         return stateListDrawable;
     }
 
-    public void show(Activity context, int title, int preselect) {
+    public void show(@NonNull Activity context, int title, int preselect) {
         Bundle args = new Bundle();
         args.putInt("preselect", preselect);
         args.putInt("title", title);

app/src/main/java/com/kabouzeid/gramophone/dialogs/CreatePlaylistDialog.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.dialogs;
 import android.app.Dialog;
 import android.os.Bundle;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.app.DialogFragment;
 import android.text.InputType;
 
@@ -18,17 +19,20 @@ import java.util.ArrayList;
  */
 public class CreatePlaylistDialog extends DialogFragment {
 
+    @NonNull
     public static CreatePlaylistDialog create() {
         return create((Song) null);
     }
 
-    public static CreatePlaylistDialog create(Song song) {
+    @NonNull
+    public static CreatePlaylistDialog create(@Nullable Song song) {
         ArrayList<Song> list = new ArrayList<>();
         if (song != null)
             list.add(song);
         return create(list);
     }
 
+    @NonNull
     public static CreatePlaylistDialog create(ArrayList<Song> songs) {
         CreatePlaylistDialog dialog = new CreatePlaylistDialog();
         Bundle args = new Bundle();
@@ -49,7 +53,7 @@ public class CreatePlaylistDialog extends DialogFragment {
                         InputType.TYPE_TEXT_FLAG_CAP_WORDS)
                 .input(R.string.playlist_name_empty, 0, false, new MaterialDialog.InputCallback() {
                     @Override
-                    public void onInput(MaterialDialog materialDialog, CharSequence charSequence) {
+                    public void onInput(MaterialDialog materialDialog, @NonNull CharSequence charSequence) {
                         if (getActivity() == null)
                             return;
                         if (!charSequence.toString().trim().isEmpty()) {

app/src/main/java/com/kabouzeid/gramophone/dialogs/DeletePlaylistDialog.java

@@ -18,12 +18,14 @@ import java.util.ArrayList;
  */
 public class DeletePlaylistDialog extends DialogFragment {
 
+    @NonNull
     public static DeletePlaylistDialog create(Playlist playlist) {
         ArrayList<Playlist> list = new ArrayList<>();
         list.add(playlist);
         return create(list);
     }
 
+    @NonNull
     public static DeletePlaylistDialog create(ArrayList<Playlist> playlists) {
         DeletePlaylistDialog dialog = new DeletePlaylistDialog();
         Bundle args = new Bundle();

app/src/main/java/com/kabouzeid/gramophone/dialogs/DeleteSongsDialog.java

@@ -18,12 +18,14 @@ import java.util.ArrayList;
  */
 public class DeleteSongsDialog extends DialogFragment {
 
+    @NonNull
     public static DeleteSongsDialog create(Song song) {
         ArrayList<Song> list = new ArrayList<>();
         list.add(song);
         return create(list);
     }
 
+    @NonNull
     public static DeleteSongsDialog create(ArrayList<Song> songs) {
         DeleteSongsDialog dialog = new DeleteSongsDialog();
         Bundle args = new Bundle();

app/src/main/java/com/kabouzeid/gramophone/dialogs/RemoveFromPlaylistDialog.java

@@ -18,12 +18,14 @@ import java.util.ArrayList;
  */
 public class RemoveFromPlaylistDialog extends DialogFragment {
 
+    @NonNull
     public static RemoveFromPlaylistDialog create(PlaylistSong song) {
         ArrayList<PlaylistSong> list = new ArrayList<>();
         list.add(song);
         return create(list);
     }
 
+    @NonNull
     public static RemoveFromPlaylistDialog create(ArrayList<PlaylistSong> songs) {
         RemoveFromPlaylistDialog dialog = new RemoveFromPlaylistDialog();
         Bundle args = new Bundle();

app/src/main/java/com/kabouzeid/gramophone/dialogs/RenamePlaylistDialog.java

@@ -15,6 +15,7 @@ import com.kabouzeid.gramophone.util.PlaylistsUtil;
  */
 public class RenamePlaylistDialog extends DialogFragment {
 
+    @NonNull
     public static RenamePlaylistDialog create(long playlistId) {
         RenamePlaylistDialog dialog = new RenamePlaylistDialog();
         Bundle args = new Bundle();
@@ -37,7 +38,7 @@ public class RenamePlaylistDialog extends DialogFragment {
                 .input(getString(R.string.playlist_name_empty), PlaylistsUtil.getNameForPlaylist(getActivity(), playlistId), false,
                         new MaterialDialog.InputCallback() {
                             @Override
-                            public void onInput(MaterialDialog materialDialog, CharSequence charSequence) {
+                            public void onInput(MaterialDialog materialDialog, @NonNull CharSequence charSequence) {
                                 if (!charSequence.toString().trim().equals("")) {
                                     long playlistId = getArguments().getLong("playlist_id");
                                     PlaylistsUtil.renamePlaylist(getActivity(), playlistId, charSequence.toString());

app/src/main/java/com/kabouzeid/gramophone/dialogs/SleepTimerDialog.java

@@ -121,7 +121,7 @@ public class SleepTimerDialog extends DialogFragment {
 
         seekArc.setOnSeekArcChangeListener(new SeekArc.OnSeekArcChangeListener() {
             @Override
-            public void onProgressChanged(SeekArc seekArc, int i, boolean b) {
+            public void onProgressChanged(@NonNull SeekArc seekArc, int i, boolean b) {
                 if (i < 1) {
                     seekArc.setProgress(1);
                     return;

app/src/main/java/com/kabouzeid/gramophone/dialogs/SongDetailDialog.java

@@ -35,6 +35,7 @@ public class SongDetailDialog extends DialogFragment {
 
     public static final String TAG = SongDetailDialog.class.getSimpleName();
 
+    @NonNull
     public static SongDetailDialog create(File songFile) {
         SongDetailDialog dialog = new SongDetailDialog();
         Bundle args = new Bundle();
@@ -85,13 +86,13 @@ public class SongDetailDialog extends DialogFragment {
                 bitRate.setText(makeTextWithTitle(context, R.string.label_bit_rate, audioHeader.getBitRate() + " kb/s"));
                 samplingRate.setText(makeTextWithTitle(context, R.string.label_sampling_rate, audioHeader.getSampleRate() + " Hz"));
             }
-        } catch (CannotReadException | IOException | TagException | ReadOnlyFileException | InvalidAudioFrameException e) {
+        } catch (@NonNull CannotReadException | IOException | TagException | ReadOnlyFileException | InvalidAudioFrameException e) {
             Log.e(TAG, "error while reading the song file", e);
         }
         return dialog;
     }
 
-    private static Spanned makeTextWithTitle(Context context, int titleResId, String text) {
+    private static Spanned makeTextWithTitle(@NonNull Context context, int titleResId, String text) {
         return Html.fromHtml("<b>" + context.getResources().getString(titleResId) + ": " + "</b>" + text);
     }
 }

app/src/main/java/com/kabouzeid/gramophone/dialogs/SongShareDialog.java

@@ -16,6 +16,7 @@ import com.kabouzeid.gramophone.util.MusicUtil;
  * @author Karim Abou Zeid (kabouzeid)
  */
 public class SongShareDialog extends DialogFragment {
+    @NonNull
     public static SongShareDialog create(final Song song) {
         final SongShareDialog dialog = new SongShareDialog();
         final Bundle args = new Bundle();

app/src/main/java/com/kabouzeid/gramophone/helper/MenuItemClickHelper.java

@@ -2,6 +2,7 @@ package com.kabouzeid.gramophone.helper;
 
 import android.app.Activity;
 import android.content.Intent;
+import android.support.annotation.NonNull;
 import android.support.v4.util.Pair;
 import android.support.v7.app.AppCompatActivity;
 import android.view.MenuItem;
@@ -31,7 +32,7 @@ import java.util.ArrayList;
  */
 public class MenuItemClickHelper {
 
-    public static boolean handleSongMenuClick(AppCompatActivity activity, Song song, MenuItem item) {
+    public static boolean handleSongMenuClick(@NonNull AppCompatActivity activity, @NonNull Song song, @NonNull MenuItem item) {
         switch (item.getItemId()) {
             case R.id.action_set_as_ringtone:
                 MusicUtil.setRingtone(activity, song.id);
@@ -78,7 +79,7 @@ public class MenuItemClickHelper {
         return false;
     }
 
-    public static boolean handlePlaylistMenuClick(AppCompatActivity activity, Playlist playlist, MenuItem item) {
+    public static boolean handlePlaylistMenuClick(@NonNull AppCompatActivity activity, @NonNull Playlist playlist, @NonNull MenuItem item) {
         switch (item.getItemId()) {
             case R.id.action_play:
                 MusicPlayerRemote.openQueue(new ArrayList<>(getPlaylistSongs(activity, playlist)), 0, true);
@@ -96,7 +97,8 @@ public class MenuItemClickHelper {
         return false;
     }
 
-    private static ArrayList<? extends Song> getPlaylistSongs(Activity activity, Playlist playlist) {
+    @NonNull
+    private static ArrayList<? extends Song> getPlaylistSongs(@NonNull Activity activity, Playlist playlist) {
         return playlist instanceof AbsSmartPlaylist ?
                 ((AbsSmartPlaylist) playlist).getSongs(activity) :
                 PlaylistSongLoader.getPlaylistSongList(activity, playlist.id);

app/src/main/java/com/kabouzeid/gramophone/helper/MusicPlayerRemote.java

@@ -8,6 +8,8 @@ import android.content.Intent;
 import android.content.ServiceConnection;
 import android.media.audiofx.AudioEffect;
 import android.os.IBinder;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.widget.Toast;
 
 import com.kabouzeid.gramophone.R;
@@ -26,11 +28,12 @@ public class MusicPlayerRemote {
 
     public static final String TAG = MusicPlayerRemote.class.getSimpleName();
 
+    @Nullable
     public static MusicService musicService;
 
     private static final WeakHashMap<Context, ServiceBinder> mConnectionMap = new WeakHashMap<>();
 
-    public static ServiceToken bindToService(final Context context,
+    public static ServiceToken bindToService(@NonNull final Context context,
                                              final ServiceConnection callback) {
         Activity realActivity = ((Activity) context).getParent();
         if (realActivity == null) {
@@ -49,7 +52,7 @@ public class MusicPlayerRemote {
         return null;
     }
 
-    public static void unbindFromService(final ServiceToken token) {
+    public static void unbindFromService(@Nullable final ServiceToken token) {
         if (token == null) {
             return;
         }
@@ -161,6 +164,7 @@ public class MusicPlayerRemote {
         return -1;
     }
 
+    @Nullable
     public static ArrayList<Song> getPlayingQueue() {
         if (musicService != null) {
             return musicService.getPlayingQueue();
@@ -226,11 +230,11 @@ public class MusicPlayerRemote {
         return false;
     }
 
-    public static boolean shuffleAllSongs(final Context context, boolean startPlaying) {
+    public static boolean shuffleAllSongs(@NonNull final Context context, boolean startPlaying) {
         return openAndShuffleQueue(context, SongLoader.getAllSongs(context), startPlaying);
     }
 
-    public static boolean openAndShuffleQueue(final Context context, final ArrayList<Song> songs, boolean startPlaying) {
+    public static boolean openAndShuffleQueue(final Context context, @NonNull final ArrayList<Song> songs, boolean startPlaying) {
         if (musicService != null) {
             if (!songs.isEmpty()) {
                 MusicPlayerRemote.openQueue(songs, new Random().nextInt(songs.size()), startPlaying);
@@ -259,7 +263,7 @@ public class MusicPlayerRemote {
         return false;
     }
 
-    public static boolean enqueue(ArrayList<Song> songs) {
+    public static boolean enqueue(@NonNull ArrayList<Song> songs) {
         if (musicService != null) {
             musicService.addSongs(songs);
             final String toast = songs.size() == 1 ? musicService.getResources().getString(R.string.added_title_to_playing_queue) : musicService.getResources().getString(R.string.added_x_titles_to_playing_queue, songs.size());
@@ -269,7 +273,7 @@ public class MusicPlayerRemote {
         return false;
     }
 
-    public static boolean removeFromQueue(Song song) {
+    public static boolean removeFromQueue(@NonNull Song song) {
         if (musicService != null) {
             musicService.removeSong(song);
             return true;

app/src/main/java/com/kabouzeid/gramophone/helper/PlayingNotificationHelper.java

@@ -13,6 +13,8 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.graphics.Bitmap;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.app.NotificationCompat;
 import android.support.v7.graphics.Palette;
 import android.view.View;
@@ -38,9 +40,12 @@ public class PlayingNotificationHelper {
     public static final String ACTION_NOTIFICATION_COLOR_PREFERENCE_CHANGED = "com.kabouzeid.gramophone.NOTIFICATION_COLOR_PREFERENCE_CHANGED";
     public static final String EXTRA_NOTIFICATION_COLORED = "com.kabouzeid.gramophone.EXTRA_NOTIFICATION_COLORED";
 
+    @NonNull
     private final MusicService service;
 
+    @NonNull
     private final NotificationManager notificationManager;
+    @Nullable
     private Notification notification = null;
 
     private RemoteViews notificationLayout;
@@ -54,9 +59,10 @@ public class PlayingNotificationHelper {
     private boolean isReceiverRegistered;
     private boolean isNotificationShown;
 
+    @NonNull
     final IntentFilter intentFilter;
 
-    public PlayingNotificationHelper(final MusicService service) {
+    public PlayingNotificationHelper(@NonNull final MusicService service) {
         this.service = service;
         notificationManager = (NotificationManager) service
                 .getSystemService(Context.NOTIFICATION_SERVICE);
@@ -65,9 +71,10 @@ public class PlayingNotificationHelper {
         intentFilter.addAction(ACTION_NOTIFICATION_COLOR_PREFERENCE_CHANGED);
     }
 
+    @NonNull
     private BroadcastReceiver notificationColorPreferenceChangedReceiver = new BroadcastReceiver() {
         @Override
-        public void onReceive(Context context, Intent intent) {
+        public void onReceive(Context context, @NonNull Intent intent) {
             if (intent.getAction().equals(ACTION_NOTIFICATION_COLOR_PREFERENCE_CHANGED)) {
                 boolean isColored = intent.getBooleanExtra(EXTRA_NOTIFICATION_COLORED, false);
                 if (isNotificationShown && PlayingNotificationHelper.this.isColored != isColored) {
@@ -219,7 +226,7 @@ public class PlayingNotificationHelper {
         });
     }
 
-    private void setAlbumArt(Bitmap albumArt) {
+    private void setAlbumArt(@Nullable Bitmap albumArt) {
         if (albumArt != null) {
             notificationLayout.setImageViewBitmap(R.id.icon, albumArt);
             notificationLayoutExpanded.setImageViewBitmap(R.id.icon, albumArt);

app/src/main/java/com/kabouzeid/gramophone/helper/SearchQueryHelper.java

@@ -4,6 +4,7 @@ import android.app.SearchManager;
 import android.content.Context;
 import android.os.Bundle;
 import android.provider.MediaStore;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.loader.SongLoader;
 import com.kabouzeid.gramophone.model.Song;
@@ -19,7 +20,8 @@ public class SearchQueryHelper {
     private static final String ARTIST_SELECTION = "lower(" + MediaStore.Audio.AudioColumns.ARTIST + ") = ?";
     private static final String AND = " AND ";
 
-    public static ArrayList<Song> getSongs(final Context context, final Bundle extras) {
+    @NonNull
+    public static ArrayList<Song> getSongs(@NonNull final Context context, @NonNull final Bundle extras) {
         final String query = extras.getString(SearchManager.QUERY, null);
         final String artistName = extras.getString(MediaStore.EXTRA_MEDIA_ARTIST, null);
         final String albumName = extras.getString(MediaStore.EXTRA_MEDIA_ALBUM, null);

app/src/main/java/com/kabouzeid/gramophone/helper/ShuffleHelper.java

@@ -1,5 +1,7 @@
 package com.kabouzeid.gramophone.helper;
 
+import android.support.annotation.NonNull;
+
 import com.kabouzeid.gramophone.model.Song;
 
 import java.util.Collections;
@@ -10,7 +12,7 @@ import java.util.List;
  */
 public class ShuffleHelper {
 
-    public static void makeShuffleList(List<Song> listToShuffle, final int current) {
+    public static void makeShuffleList(@NonNull List<Song> listToShuffle, final int current) {
         if (current >= 0) {
             Song song = listToShuffle.remove(current);
             Collections.shuffle(listToShuffle);

app/src/main/java/com/kabouzeid/gramophone/helper/bitmapblur/BlurProcess.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.helper.bitmapblur;
 
 import android.graphics.Bitmap;
+import android.support.annotation.Nullable;
 
 interface BlurProcess {
     /**
@@ -11,5 +12,6 @@ interface BlurProcess {
      * @param radius   the radius in pixels to blur the image
      * @return the blurred version of the image.
      */
+    @Nullable
     Bitmap blur(Bitmap original, float radius);
 }

app/src/main/java/com/kabouzeid/gramophone/helper/bitmapblur/JavaBlurProcess.java

@@ -1,6 +1,8 @@
 package com.kabouzeid.gramophone.helper.bitmapblur;
 
 import android.graphics.Bitmap;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import java.util.ArrayList;
 import java.util.concurrent.Callable;
@@ -71,8 +73,9 @@ class JavaBlurProcess implements BlurProcess {
             24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24
     };
 
+    @Nullable
     @Override
-    public Bitmap blur(Bitmap original, float radius) {
+    public Bitmap blur(@NonNull Bitmap original, float radius) {
         int w = original.getWidth();
         int h = original.getHeight();
         int[] currentPixels = new int[w * h];
@@ -319,6 +322,7 @@ class JavaBlurProcess implements BlurProcess {
             _round = round;
         }
 
+        @Nullable
         @Override
         public Void call() throws Exception {
             blurIteration(_src, _w, _h, _radius, _totalCores, _coreIndex, _round);

app/src/main/java/com/kabouzeid/gramophone/helper/bitmapblur/StackBlurManager.java

@@ -26,6 +26,8 @@
 package com.kabouzeid.gramophone.helper.bitmapblur;
 
 import android.graphics.Bitmap;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.util.Util;
 
@@ -46,11 +48,13 @@ public class StackBlurManager {
     /**
      * Most recent result of blurring
      */
+    @Nullable
     private Bitmap _result;
 
     /**
      * Method of blurring
      */
+    @NonNull
     private final BlurProcess _blurProcess;
 
     /**
@@ -58,7 +62,7 @@ public class StackBlurManager {
      *
      * @param image The image that will be analysed
      */
-    public StackBlurManager(Bitmap image) {
+    public StackBlurManager(@NonNull Bitmap image) {
         _image = Util.getResizedBitmap(image, 500, 500, false);
         _blurProcess = new JavaBlurProcess();
     }
@@ -68,6 +72,7 @@ public class StackBlurManager {
      *
      * @param radius
      */
+    @Nullable
     public Bitmap process(int radius) {
         _result = _blurProcess.blur(_image, radius);
         return _result;
@@ -78,6 +83,7 @@ public class StackBlurManager {
      *
      * @return blurred image
      */
+    @Nullable
     public Bitmap returnBlurredImage() {
         return _result;
     }

app/src/main/java/com/kabouzeid/gramophone/imageloader/PhonographImageDownloader.java

@@ -2,6 +2,8 @@ package com.kabouzeid.gramophone.imageloader;
 
 import android.content.Context;
 import android.graphics.Bitmap;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.loader.AlbumSongLoader;
 import com.kabouzeid.gramophone.model.Song;
@@ -24,12 +26,13 @@ public class PhonographImageDownloader extends BaseImageDownloader {
     public static final String SCHEME_ALBUM = "album://";
     public static final String SCHEME_SONG = "song://";
 
-    public PhonographImageDownloader(Context context) {
+    public PhonographImageDownloader(@NonNull Context context) {
         super(context);
     }
 
+    @Nullable
     @Override
-    protected InputStream getStreamFromOtherSource(String imageUri, Object extra) throws IOException {
+    protected InputStream getStreamFromOtherSource(@NonNull String imageUri, Object extra) throws IOException {
         if (imageUri.startsWith(SCHEME_ALBUM)) {
             return getStreamFromAlbum(imageUri, extra);
         } else if (imageUri.startsWith(SCHEME_SONG)) {
@@ -39,7 +42,8 @@ public class PhonographImageDownloader extends BaseImageDownloader {
         }
     }
 
-    protected InputStream getStreamFromAlbum(String imageUri, Object extra) throws IOException {
+    @Nullable
+    protected InputStream getStreamFromAlbum(@NonNull String imageUri, Object extra) throws IOException {
         int albumId = Integer.valueOf(imageUri.substring(SCHEME_ALBUM.length()));
 
         if (PreferenceUtils.getInstance(context).ignoreMediaStoreArtwork()) {
@@ -55,7 +59,8 @@ public class PhonographImageDownloader extends BaseImageDownloader {
         return getStream(MusicUtil.getAlbumArtUri(albumId).toString(), extra);
     }
 
-    protected InputStream getStreamFromSong(String imageUri, Object extra) throws IOException {
+    @Nullable
+    protected InputStream getStreamFromSong(@NonNull String imageUri, Object extra) throws IOException {
         String[] data = imageUri.split("#", 2);
 
         if (PreferenceUtils.getInstance(context).ignoreMediaStoreArtwork()) {
@@ -70,7 +75,8 @@ public class PhonographImageDownloader extends BaseImageDownloader {
         return getStream(MusicUtil.getAlbumArtUri(id).toString(), extra);
     }
 
-    private static ByteArrayInputStream getBitmapInputStream(Bitmap bitmap) {
+    @NonNull
+    private static ByteArrayInputStream getBitmapInputStream(@NonNull Bitmap bitmap) {
         ByteArrayOutputStream bos = new ByteArrayOutputStream();
         bitmap.compress(Bitmap.CompressFormat.JPEG, 100, bos);
         return new ByteArrayInputStream(bos.toByteArray());

app/src/main/java/com/kabouzeid/gramophone/lastfm/rest/LastFMRestClient.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.lastfm.rest;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.lastfm.rest.service.LastFMService;
 import com.squareup.okhttp.Cache;
@@ -20,7 +21,7 @@ public class LastFMRestClient {
 
     private LastFMService apiService;
 
-    public LastFMRestClient(Context context) {
+    public LastFMRestClient(@NonNull Context context) {
         OkHttpClient okHttpClient = new OkHttpClient();
 
         File cacheDir = new File(context.getCacheDir().getAbsolutePath(), "/okhttp-lastfm/");
@@ -33,7 +34,7 @@ public class LastFMRestClient {
                 .setClient(new OkClient(okHttpClient))
                 .setRequestInterceptor(new RequestInterceptor() {
                     @Override
-                    public void intercept(RequestInterceptor.RequestFacade request) {
+                    public void intercept(@NonNull RequestInterceptor.RequestFacade request) {
                         request.addHeader("Cache-Control", String.format("max-age=%d, max-stale=%d", 31536000, 31536000));
                     }
                 })

app/src/main/java/com/kabouzeid/gramophone/loader/AlbumLoader.java

@@ -7,6 +7,8 @@ import android.provider.BaseColumns;
 import android.provider.MediaStore;
 import android.provider.MediaStore.Audio.AlbumColumns;
 import android.provider.MediaStore.Audio.AudioColumns;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.model.Album;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -18,22 +20,26 @@ import java.util.ArrayList;
  */
 public class AlbumLoader {
 
-    public static ArrayList<Album> getAllAlbums(final Context context) {
+    @NonNull
+    public static ArrayList<Album> getAllAlbums(@NonNull final Context context) {
         Cursor cursor = makeAlbumCursor(context, null, null);
         return getAlbums(cursor);
     }
 
-    public static ArrayList<Album> getAlbums(final Context context, String query) {
+    @NonNull
+    public static ArrayList<Album> getAlbums(@NonNull final Context context, String query) {
         Cursor cursor = makeAlbumCursor(context, AlbumColumns.ALBUM + " LIKE ?", new String[]{"%" + query + "%"});
         return getAlbums(cursor);
     }
 
-    public static Album getAlbum(final Context context, int albumId) {
+    @NonNull
+    public static Album getAlbum(@NonNull final Context context, int albumId) {
         Cursor cursor = makeAlbumCursor(context, BaseColumns._ID + "=?", new String[]{String.valueOf(albumId)});
         return getAlbum(cursor);
     }
 
-    public static ArrayList<Album> getAlbums(final Cursor cursor) {
+    @NonNull
+    public static ArrayList<Album> getAlbums(@Nullable final Cursor cursor) {
         ArrayList<Album> albums = new ArrayList<>();
         if (cursor != null && cursor.moveToFirst()) {
             do {
@@ -46,7 +52,8 @@ public class AlbumLoader {
         return albums;
     }
 
-    public static Album getAlbum(final Cursor cursor) {
+    @NonNull
+    public static Album getAlbum(@Nullable final Cursor cursor) {
         Album album = new Album();
         if (cursor != null && cursor.moveToFirst()) {
             album = getAlbumFromCursorImpl(cursor);
@@ -58,7 +65,8 @@ public class AlbumLoader {
         return album;
     }
 
-    private static Album getAlbumFromCursorImpl(final Cursor cursor) {
+    @NonNull
+    private static Album getAlbumFromCursorImpl(@NonNull final Cursor cursor) {
         final int id = cursor.getInt(0);
         final String albumName = cursor.getString(1);
         final String artist = cursor.getString(2);
@@ -69,15 +77,15 @@ public class AlbumLoader {
         return new Album(id, albumName, artist, artistId, songCount, year);
     }
 
-    public static Cursor makeAlbumCursor(final Context context, final String selection, final String[] values) {
+    public static Cursor makeAlbumCursor(@NonNull final Context context, final String selection, final String[] values) {
         return makeAlbumCursor(context, selection, values, PreferenceUtils.getInstance(context).getAlbumSortOrder());
     }
 
-    public static Cursor makeAlbumCursor(final Context context, final String selection, final String[] values, final String sortOrder) {
+    public static Cursor makeAlbumCursor(@NonNull final Context context, final String selection, final String[] values, final String sortOrder) {
         return makeAlbumCursor(context, MediaStore.Audio.Albums.EXTERNAL_CONTENT_URI, selection, values, sortOrder);
     }
 
-    public static Cursor makeAlbumCursor(final Context context, final Uri contentUri, final String selection, final String[] values, final String sortOrder) {
+    public static Cursor makeAlbumCursor(@NonNull final Context context, @NonNull final Uri contentUri, final String selection, final String[] values, final String sortOrder) {
         return context.getContentResolver().query(contentUri,
                 new String[]{
                         /* 0 */

app/src/main/java/com/kabouzeid/gramophone/loader/AlbumSongLoader.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.loader;
 import android.content.Context;
 import android.database.Cursor;
 import android.provider.MediaStore;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.model.Song;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -14,11 +15,12 @@ import java.util.ArrayList;
  */
 public class AlbumSongLoader {
 
-    public static ArrayList<Song> getAlbumSongList(final Context context, final int albumId) {
+    @NonNull
+    public static ArrayList<Song> getAlbumSongList(@NonNull final Context context, final int albumId) {
         return SongLoader.getSongs(makeAlbumSongCursor(context, albumId));
     }
 
-    public static Cursor makeAlbumSongCursor(final Context context, final int albumId) {
+    public static Cursor makeAlbumSongCursor(@NonNull final Context context, final int albumId) {
         return SongLoader.makeSongCursor(
                 context,
                 MediaStore.Audio.AudioColumns.ALBUM_ID + "=?",

app/src/main/java/com/kabouzeid/gramophone/loader/ArtistAlbumLoader.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.loader;
 import android.content.Context;
 import android.database.Cursor;
 import android.provider.MediaStore;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.model.Album;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -14,11 +15,12 @@ import java.util.ArrayList;
  */
 public class ArtistAlbumLoader {
 
-    public static ArrayList<Album> getArtistAlbumList(final Context context, final int artistId) {
+    @NonNull
+    public static ArrayList<Album> getArtistAlbumList(@NonNull final Context context, final int artistId) {
         return AlbumLoader.getAlbums(makeArtistAlbumCursor(context, artistId));
     }
 
-    public static Cursor makeArtistAlbumCursor(final Context context, final int artistId) {
+    public static Cursor makeArtistAlbumCursor(@NonNull final Context context, final int artistId) {
         return AlbumLoader.makeAlbumCursor(context,
                 MediaStore.Audio.Artists.Albums.getContentUri("external", artistId),
                 null,

app/src/main/java/com/kabouzeid/gramophone/loader/ArtistLoader.java

@@ -5,6 +5,8 @@ import android.database.Cursor;
 import android.provider.BaseColumns;
 import android.provider.MediaStore;
 import android.provider.MediaStore.Audio.ArtistColumns;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.model.Artist;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -16,22 +18,26 @@ import java.util.ArrayList;
  */
 public class ArtistLoader {
 
-    public static ArrayList<Artist> getAllArtists(Context context) {
+    @NonNull
+    public static ArrayList<Artist> getAllArtists(@NonNull Context context) {
         Cursor cursor = makeArtistCursor(context, null, null);
         return getArtists(cursor);
     }
 
-    public static ArrayList<Artist> getArtists(Context context, String query) {
+    @NonNull
+    public static ArrayList<Artist> getArtists(@NonNull Context context, String query) {
         Cursor cursor = makeArtistCursor(context, ArtistColumns.ARTIST + " LIKE ?", new String[]{"%" + query + "%"});
         return getArtists(cursor);
     }
 
-    public static Artist getArtist(Context context, int artistId) {
+    @NonNull
+    public static Artist getArtist(@NonNull Context context, int artistId) {
         Cursor cursor = makeArtistCursor(context, BaseColumns._ID + "=?", new String[]{String.valueOf(artistId)});
         return getArtist(cursor);
     }
 
-    public static ArrayList<Artist> getArtists(Cursor cursor) {
+    @NonNull
+    public static ArrayList<Artist> getArtists(@Nullable Cursor cursor) {
         ArrayList<Artist> artists = new ArrayList<>();
         if (cursor != null && cursor.moveToFirst()) {
             do {
@@ -45,7 +51,8 @@ public class ArtistLoader {
         return artists;
     }
 
-    public static Artist getArtist(Cursor cursor) {
+    @NonNull
+    public static Artist getArtist(@Nullable Cursor cursor) {
         Artist artist = new Artist();
         if (cursor != null && cursor.moveToFirst()) {
             artist = getArtistFromCursorImpl(cursor);
@@ -57,7 +64,8 @@ public class ArtistLoader {
         return artist;
     }
 
-    private static Artist getArtistFromCursorImpl(Cursor cursor) {
+    @NonNull
+    private static Artist getArtistFromCursorImpl(@NonNull Cursor cursor) {
         final int id = cursor.getInt(0);
         final String artistName = cursor.getString(1);
         final int albumCount = cursor.getInt(2);
@@ -66,7 +74,7 @@ public class ArtistLoader {
         return new Artist(id, artistName, albumCount, songCount);
     }
 
-    public static Cursor makeArtistCursor(final Context context, final String selection, final String[] values) {
+    public static Cursor makeArtistCursor(@NonNull final Context context, final String selection, final String[] values) {
         return context.getContentResolver().query(MediaStore.Audio.Artists.EXTERNAL_CONTENT_URI,
                 new String[]{
                         /* 0 */

app/src/main/java/com/kabouzeid/gramophone/loader/ArtistSongLoader.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.loader;
 import android.content.Context;
 import android.database.Cursor;
 import android.provider.MediaStore;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.model.Song;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -14,11 +15,12 @@ import java.util.ArrayList;
  */
 public class ArtistSongLoader {
 
-    public static ArrayList<Song> getArtistSongList(final Context context, final int artistId) {
+    @NonNull
+    public static ArrayList<Song> getArtistSongList(@NonNull final Context context, final int artistId) {
         return SongLoader.getSongs(makeArtistSongCursor(context, artistId));
     }
 
-    public static Cursor makeArtistSongCursor(final Context context, final int artistId) {
+    public static Cursor makeArtistSongCursor(@NonNull final Context context, final int artistId) {
         return SongLoader.makeSongCursor(
                 context,
                 MediaStore.Audio.AudioColumns.ARTIST_ID + "=?",

app/src/main/java/com/kabouzeid/gramophone/loader/LastAddedLoader.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.loader;
 import android.content.Context;
 import android.database.Cursor;
 import android.provider.MediaStore;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.model.Song;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -11,11 +12,12 @@ import java.util.ArrayList;
 
 public class LastAddedLoader {
 
-    public static ArrayList<Song> getLastAddedSongs(Context context) {
+    @NonNull
+    public static ArrayList<Song> getLastAddedSongs(@NonNull Context context) {
         return SongLoader.getSongs(makeLastAddedCursor(context));
     }
 
-    public static Cursor makeLastAddedCursor(final Context context) {
+    public static Cursor makeLastAddedCursor(@NonNull final Context context) {
         long fourWeeksAgo = (System.currentTimeMillis() / 1000) - (4 * 3600 * 24 * 7);
         // possible saved timestamp caused by user "clearing" the last added playlist
         long cutoff = PreferenceUtils.getInstance(context).getLastAddedCutOffTimestamp() / 1000;

app/src/main/java/com/kabouzeid/gramophone/loader/PlaylistLoader.java

@@ -5,6 +5,8 @@ import android.database.Cursor;
 import android.provider.BaseColumns;
 import android.provider.MediaStore;
 import android.provider.MediaStore.Audio.PlaylistsColumns;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.model.Playlist;
 
@@ -13,11 +15,13 @@ import java.util.List;
 
 public class PlaylistLoader {
 
-    public static List<Playlist> getAllPlaylists(final Context context) {
+    @NonNull
+    public static List<Playlist> getAllPlaylists(@NonNull final Context context) {
         return getAllPlaylists(makePlaylistCursor(context, null, null));
     }
 
-    public static Playlist getPlaylist(final Context context, final int playlistId) {
+    @NonNull
+    public static Playlist getPlaylist(@NonNull final Context context, final int playlistId) {
         return getPlaylist(makePlaylistCursor(
                 context,
                 BaseColumns._ID + "=?",
@@ -27,7 +31,8 @@ public class PlaylistLoader {
         ));
     }
 
-    public static Playlist getPlaylist(final Context context, final String playlistName) {
+    @NonNull
+    public static Playlist getPlaylist(@NonNull final Context context, final String playlistName) {
         return getPlaylist(makePlaylistCursor(
                 context,
                 PlaylistsColumns.NAME + "=?",
@@ -37,7 +42,8 @@ public class PlaylistLoader {
         ));
     }
 
-    public static Playlist getPlaylist(final Cursor cursor) {
+    @NonNull
+    public static Playlist getPlaylist(@Nullable final Cursor cursor) {
         Playlist playlist = new Playlist();
 
         if (cursor != null && cursor.moveToFirst()) {
@@ -48,7 +54,8 @@ public class PlaylistLoader {
         return playlist;
     }
 
-    public static List<Playlist> getAllPlaylists(final Cursor cursor) {
+    @NonNull
+    public static List<Playlist> getAllPlaylists(@Nullable final Cursor cursor) {
         List<Playlist> playlists = new ArrayList<>();
 
         if (cursor != null && cursor.moveToFirst()) {
@@ -61,13 +68,14 @@ public class PlaylistLoader {
         return playlists;
     }
 
-    private static Playlist getPlaylistFromCursorImpl(final Cursor cursor) {
+    @NonNull
+    private static Playlist getPlaylistFromCursorImpl(@NonNull final Cursor cursor) {
         final int id = cursor.getInt(0);
         final String name = cursor.getString(1);
         return new Playlist(id, name);
     }
 
-    public static Cursor makePlaylistCursor(final Context context, final String selection, final String[] values) {
+    public static Cursor makePlaylistCursor(@NonNull final Context context, final String selection, final String[] values) {
         return context.getContentResolver().query(MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI,
                 new String[]{
                         /* 0 */

app/src/main/java/com/kabouzeid/gramophone/loader/PlaylistSongLoader.java

@@ -4,6 +4,7 @@ import android.content.Context;
 import android.database.Cursor;
 import android.provider.MediaStore;
 import android.provider.MediaStore.Audio.AudioColumns;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.model.PlaylistSong;
 
@@ -11,7 +12,8 @@ import java.util.ArrayList;
 
 public class PlaylistSongLoader {
 
-    public static ArrayList<PlaylistSong> getPlaylistSongList(final Context context, final int playlistId) {
+    @NonNull
+    public static ArrayList<PlaylistSong> getPlaylistSongList(@NonNull final Context context, final int playlistId) {
         ArrayList<PlaylistSong> songs = new ArrayList<>();
         Cursor cursor = makePlaylistSongCursor(context, playlistId);
 
@@ -26,7 +28,8 @@ public class PlaylistSongLoader {
         return songs;
     }
 
-    private static PlaylistSong getPlaylistSongFromCursorImpl(Cursor cursor) {
+    @NonNull
+    private static PlaylistSong getPlaylistSongFromCursorImpl(@NonNull Cursor cursor) {
         final int id = cursor.getInt(0);
         final String songName = cursor.getString(1);
         final String artist = cursor.getString(2);
@@ -42,7 +45,7 @@ public class PlaylistSongLoader {
         return new PlaylistSong(id, albumId, artistId, songName, artist, album, duration, trackNumber, data, playlistId, idInPlaylist);
     }
 
-    public static Cursor makePlaylistSongCursor(final Context context, final int playlistId) {
+    public static Cursor makePlaylistSongCursor(@NonNull final Context context, final int playlistId) {
         return context.getContentResolver().query(
                 MediaStore.Audio.Playlists.Members.getContentUri("external", playlistId),
                 new String[]{

app/src/main/java/com/kabouzeid/gramophone/loader/SongLoader.java

@@ -5,6 +5,8 @@ import android.database.Cursor;
 import android.provider.BaseColumns;
 import android.provider.MediaStore;
 import android.provider.MediaStore.Audio.AudioColumns;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.model.Song;
 import com.kabouzeid.gramophone.util.PreferenceUtils;
@@ -17,22 +19,26 @@ import java.util.ArrayList;
 public class SongLoader {
     protected static final String BASE_SELECTION = AudioColumns.IS_MUSIC + "=1" + " AND " + AudioColumns.TITLE + " != ''";
 
-    public static ArrayList<Song> getAllSongs(Context context) {
+    @NonNull
+    public static ArrayList<Song> getAllSongs(@NonNull Context context) {
         Cursor cursor = makeSongCursor(context, null, null);
         return getSongs(cursor);
     }
 
-    public static ArrayList<Song> getSongs(final Context context, final String query) {
+    @NonNull
+    public static ArrayList<Song> getSongs(@NonNull final Context context, final String query) {
         Cursor cursor = makeSongCursor(context, AudioColumns.TITLE + " LIKE ?", new String[]{"%" + query + "%"});
         return getSongs(cursor);
     }
 
-    public static Song getSong(final Context context, final int queryId) {
+    @NonNull
+    public static Song getSong(@NonNull final Context context, final int queryId) {
         Cursor cursor = makeSongCursor(context, AudioColumns._ID + "=?", new String[]{String.valueOf(queryId)});
         return getSong(cursor);
     }
 
-    public static ArrayList<Song> getSongs(final Cursor cursor) {
+    @NonNull
+    public static ArrayList<Song> getSongs(@Nullable final Cursor cursor) {
         ArrayList<Song> songs = new ArrayList<>();
         if (cursor != null && cursor.moveToFirst()) {
             do {
@@ -45,7 +51,8 @@ public class SongLoader {
         return songs;
     }
 
-    public static Song getSong(Cursor cursor) {
+    @NonNull
+    public static Song getSong(@Nullable Cursor cursor) {
         Song song = new Song();
         if (cursor != null && cursor.moveToFirst()) {
             song = getSongFromCursorImpl(cursor);
@@ -56,7 +63,8 @@ public class SongLoader {
         return song;
     }
 
-    private static Song getSongFromCursorImpl(Cursor cursor) {
+    @NonNull
+    private static Song getSongFromCursorImpl(@NonNull Cursor cursor) {
         final int id = cursor.getInt(0);
         final String songName = cursor.getString(1);
         final String artist = cursor.getString(2);
@@ -69,11 +77,11 @@ public class SongLoader {
         return new Song(id, albumId, artistId, songName, artist, album, duration, trackNumber, data);
     }
 
-    public static Cursor makeSongCursor(final Context context, final String selection, final String[] values) {
+    public static Cursor makeSongCursor(@NonNull final Context context, final String selection, final String[] values) {
         return makeSongCursor(context, selection, values, PreferenceUtils.getInstance(context).getSongSortOrder());
     }
 
-    public static Cursor makeSongCursor(final Context context, final String selection, final String[] values, final String sortOrder) {
+    public static Cursor makeSongCursor(@NonNull final Context context, @Nullable final String selection, final String[] values, final String sortOrder) {
         String baseSelection = BASE_SELECTION;
         if (selection != null && !selection.trim().equals("")) {
             baseSelection += " AND " + selection;

app/src/main/java/com/kabouzeid/gramophone/loader/SortedCursor.java

@@ -17,6 +17,8 @@ package com.kabouzeid.gramophone.loader;
 
 import android.database.AbstractCursor;
 import android.database.Cursor;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -30,6 +32,7 @@ import java.util.List;
  */
 public class SortedCursor extends AbstractCursor {
     // cursor to wrap
+    @Nullable
     private final Cursor mCursor;
     // the map of external indices to internal indices
     private ArrayList<Integer> mOrderedPositions;
@@ -45,8 +48,8 @@ public class SortedCursor extends AbstractCursor {
      * @param order      the list of unique ids in sorted order to display
      * @param columnName the column name of the id to look up in the internal cursor
      */
-    public SortedCursor(final Cursor cursor, final long[] order, final String columnName,
+    public SortedCursor(@Nullable final Cursor cursor, final long[] order, final String columnName,
-                        final List<? extends Object> extraData) {
+                        final List<?> extraData) {
         if (cursor == null) {
             throw new IllegalArgumentException("Non-null cursor is needed");
         }
@@ -63,14 +66,15 @@ public class SortedCursor extends AbstractCursor {
      * @param extraData Extra data we want to add to the cursor
      * @return returns the ids that aren't found in the underlying cursor
      */
-    private ArrayList<Long> buildCursorPositionMapping(final long[] order,
+    @NonNull
-                                                       final String columnName, final List<? extends Object> extraData) {
+    private ArrayList<Long> buildCursorPositionMapping(@Nullable final long[] order,
-        ArrayList<Long> missingIds = new ArrayList<Long>();
+                                                       final String columnName, @Nullable final List<?> extraData) {
+        ArrayList<Long> missingIds = new ArrayList<>();
 
-        mOrderedPositions = new ArrayList<Integer>(mCursor.getCount());
+        mOrderedPositions = new ArrayList<>(mCursor.getCount());
-        mExtraData = new ArrayList<Object>();
+        mExtraData = new ArrayList<>();
 
-        mMapCursorPositions = new HashMap<Long, Integer>(mCursor.getCount());
+        mMapCursorPositions = new HashMap<>(mCursor.getCount());
         final int idPosition = mCursor.getColumnIndex(columnName);
 
         if (mCursor.moveToFirst()) {
@@ -110,6 +114,7 @@ public class SortedCursor extends AbstractCursor {
     /**
      * @return the list of ids that were in the underlying cursor but not part of the ordered list
      */
+    @NonNull
     public Collection<Long> getExtraIds() {
         return mMapCursorPositions.keySet();
     }
@@ -117,6 +122,7 @@ public class SortedCursor extends AbstractCursor {
     /**
      * @return the extra object data that was passed in to be attached to the current row
      */
+    @Nullable
     public Object getExtraData() {
         int position = getPosition();
         return position < mExtraData.size() ? mExtraData.get(position) : null;

app/src/main/java/com/kabouzeid/gramophone/loader/TopAndRecentlyPlayedTracksLoader.java

@@ -19,6 +19,8 @@ package com.kabouzeid.gramophone.loader;
 import android.content.Context;
 import android.database.Cursor;
 import android.provider.BaseColumns;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.model.Song;
 import com.kabouzeid.gramophone.provider.RecentlyPlayedStore;
@@ -29,15 +31,18 @@ import java.util.ArrayList;
 public class TopAndRecentlyPlayedTracksLoader {
     public static final int NUMBER_OF_TOP_TRACKS = 99;
 
-    public static ArrayList<Song> getRecentlyPlayedTracks(Context context) {
+    @NonNull
+    public static ArrayList<Song> getRecentlyPlayedTracks(@NonNull Context context) {
         return SongLoader.getSongs(makeRecentTracksCursorAndClearUpDatabase(context));
     }
 
-    public static ArrayList<Song> getTopTracks(Context context) {
+    @NonNull
+    public static ArrayList<Song> getTopTracks(@NonNull Context context) {
         return SongLoader.getSongs(makeTopTracksCursorAndClearUpDatabase(context));
     }
 
-    public static Cursor makeRecentTracksCursorAndClearUpDatabase(final Context context) {
+    @Nullable
+    public static Cursor makeRecentTracksCursorAndClearUpDatabase(@NonNull final Context context) {
         SortedCursor retCursor = makeRecentTracksCursorImpl(context);
 
         // clean up the databases with any ids not found
@@ -52,7 +57,8 @@ public class TopAndRecentlyPlayedTracksLoader {
         return retCursor;
     }
 
-    public static Cursor makeTopTracksCursorAndClearUpDatabase(final Context context) {
+    @Nullable
+    public static Cursor makeTopTracksCursorAndClearUpDatabase(@NonNull final Context context) {
         SortedCursor retCursor = makeTopTracksCursorImpl(context);
 
         // clean up the databases with any ids not found
@@ -67,7 +73,8 @@ public class TopAndRecentlyPlayedTracksLoader {
         return retCursor;
     }
 
-    private static SortedCursor makeRecentTracksCursorImpl(final Context context) {
+    @Nullable
+    private static SortedCursor makeRecentTracksCursorImpl(@NonNull final Context context) {
         // first get the top results ids from the internal database
         Cursor songs = RecentlyPlayedStore.getInstance(context).queryRecentIds();
 
@@ -81,7 +88,8 @@ public class TopAndRecentlyPlayedTracksLoader {
         }
     }
 
-    private static SortedCursor makeTopTracksCursorImpl(final Context context) {
+    @Nullable
+    private static SortedCursor makeTopTracksCursorImpl(@NonNull final Context context) {
         // first get the top results ids from the internal database
         Cursor songs = SongPlayCountStore.getInstance(context).getTopPlayedResults(NUMBER_OF_TOP_TRACKS);
 
@@ -95,7 +103,8 @@ public class TopAndRecentlyPlayedTracksLoader {
         }
     }
 
-    private static SortedCursor makeSortedCursor(final Context context, final Cursor cursor,
+    @Nullable
+    private static SortedCursor makeSortedCursor(@NonNull final Context context, @Nullable final Cursor cursor,
                                                  final int idColumn) {
         if (cursor != null && cursor.moveToFirst()) {
             // create the list of ids to select against

app/src/main/java/com/kabouzeid/gramophone/misc/DragSortRecycler.java

@@ -26,6 +26,7 @@ import android.graphics.Canvas;
 import android.graphics.Paint;
 import android.graphics.Rect;
 import android.graphics.drawable.BitmapDrawable;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v7.widget.RecyclerView;
 import android.util.Log;
@@ -52,6 +53,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
     private float autoScrollWindow = 0.1f;
     private float autoScrollSpeed = 0.5f;
 
+    @Nullable
     private BitmapDrawable floatingItem;
     private Rect floatingItemStatingBounds;
     private Rect floatingItemBounds;
@@ -85,6 +87,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
             Log.d(TAG, log);
     }
 
+    @NonNull
     public RecyclerView.OnScrollListener getScrollListener() {
         return scrollListener;
     }
@@ -128,7 +131,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
     }
 
     @Override
-    public void getItemOffsets(Rect outRect, View view, RecyclerView rv, RecyclerView.State state) {
+    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView rv, RecyclerView.State state) {
         super.getItemOffsets(outRect, view, rv, state);
 
         debugLog("getItemOffsets");
@@ -195,7 +198,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
      * This *seems* to work, another method would be to use
      * getItemOffsets, but I think that could miss items?..
      */
-    private int getNewPostion(RecyclerView rv) {
+    private int getNewPostion(@NonNull RecyclerView rv) {
         int itemsOnScreen = rv.getLayoutManager().getChildCount();
 
         float floatMiddleY = floatingItemBounds.top + floatingItemBounds.height() / 2;
@@ -242,7 +245,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
 
 
     @Override
-    public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
+    public boolean onInterceptTouchEvent(@NonNull RecyclerView rv, @NonNull MotionEvent e) {
         debugLog("onInterceptTouchEvent");
 
         //if (e.getAction() == MotionEvent.ACTION_DOWN)
@@ -315,7 +318,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
     }
 
     @Override
-    public void onTouchEvent(RecyclerView rv, MotionEvent e) {
+    public void onTouchEvent(@NonNull RecyclerView rv, @NonNull MotionEvent e) {
         debugLog("onTouchEvent");
 
         if ((e.getAction() == MotionEvent.ACTION_UP) ||
@@ -388,7 +391,7 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
     final Paint bgColor = new Paint();
 
     @Override
-    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
+    public void onDrawOver(@NonNull Canvas c, RecyclerView parent, RecyclerView.State state) {
         if (floatingItem != null) {
             floatingItem.setAlpha((int) (255 * floatingItemAlpha));
             bgColor.setColor(floatingItemBgColor);
@@ -410,7 +413,8 @@ public class DragSortRecycler extends RecyclerView.ItemDecoration implements Rec
         return true;
     }
 
-    private BitmapDrawable createFloatingBitmap(View v) {
+    @NonNull
+    private BitmapDrawable createFloatingBitmap(@NonNull View v) {
         floatingItemStatingBounds = new Rect(v.getLeft(), v.getTop(), v.getRight(), v.getBottom());
         floatingItemBounds = new Rect(floatingItemStatingBounds);
 

app/src/main/java/com/kabouzeid/gramophone/model/Album.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.model;
 
+import android.support.annotation.Nullable;
 import android.text.TextUtils;
 
 /**
@@ -46,7 +47,7 @@ public class Album {
     }
 
     @Override
-    public boolean equals(final Object obj) {
+    public boolean equals(@Nullable final Object obj) {
         if (this == obj) {
             return true;
         }

app/src/main/java/com/kabouzeid/gramophone/model/Artist.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.model;
 
+import android.support.annotation.Nullable;
 import android.text.TextUtils;
 
 /**
@@ -37,7 +38,7 @@ public class Artist {
     }
 
     @Override
-    public boolean equals(final Object obj) {
+    public boolean equals(@Nullable final Object obj) {
         if (this == obj) {
             return true;
         }

app/src/main/java/com/kabouzeid/gramophone/model/Playlist.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.model;
 
+import android.support.annotation.Nullable;
 import android.text.TextUtils;
 
 import java.io.Serializable;
@@ -34,7 +35,7 @@ public class Playlist implements Serializable {
     }
 
     @Override
-    public boolean equals(final Object obj) {
+    public boolean equals(@Nullable final Object obj) {
         if (this == obj) {
             return true;
         }

app/src/main/java/com/kabouzeid/gramophone/model/Song.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.model;
 
+import android.support.annotation.Nullable;
 import android.text.TextUtils;
 
 import java.io.Serializable;
@@ -59,7 +60,7 @@ public class Song implements Serializable {
     }
 
     @Override
-    public boolean equals(final Object obj) {
+    public boolean equals(@Nullable final Object obj) {
         if (this == obj) {
             return true;
         }

app/src/main/java/com/kabouzeid/gramophone/model/smartplaylist/AbsSmartPlaylist.java

@@ -2,6 +2,7 @@ package com.kabouzeid.gramophone.model.smartplaylist;
 
 import android.content.Context;
 import android.support.annotation.DrawableRes;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 
@@ -32,6 +33,7 @@ public abstract class AbsSmartPlaylist extends Playlist {
         this.iconRes = R.drawable.ic_queue_music_white_24dp;
     }
 
+    @Nullable
     public SmartPlaylistSongAdapter createAdapter(AppCompatActivity activity, @Nullable CabHolder cabHolder) {
         return new SmartPlaylistSongAdapter(activity, this, cabHolder);
     }
@@ -49,7 +51,7 @@ public abstract class AbsSmartPlaylist extends Playlist {
     }
 
     @Override
-    public boolean equals(final Object obj) {
+    public boolean equals(@NonNull final Object obj) {
         if (super.equals(obj)) {
             if (getClass() != obj.getClass()) {
                 return false;

app/src/main/java/com/kabouzeid/gramophone/model/smartplaylist/LastAddedPlaylist.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.model.smartplaylist;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.App;
 import com.kabouzeid.gramophone.R;
@@ -16,17 +17,18 @@ import java.util.ArrayList;
  */
 public class LastAddedPlaylist extends AbsSmartPlaylist {
 
-    public LastAddedPlaylist(Context context) {
+    public LastAddedPlaylist(@NonNull Context context) {
         super(context.getString(R.string.last_added), R.drawable.ic_queue_white_24dp);
     }
 
+    @NonNull
     @Override
-    public ArrayList<Song> getSongs(Context context) {
+    public ArrayList<Song> getSongs(@NonNull Context context) {
         return LastAddedLoader.getLastAddedSongs(context);
     }
 
     @Override
-    public void clear(Context context) {
+    public void clear(@NonNull Context context) {
         PreferenceUtils.getInstance(context).setLastAddedCutoffTimestamp(System.currentTimeMillis());
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }

app/src/main/java/com/kabouzeid/gramophone/model/smartplaylist/MyTopTracksPlaylist.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.model.smartplaylist;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.App;
 import com.kabouzeid.gramophone.R;
@@ -16,17 +17,18 @@ import java.util.ArrayList;
  */
 public class MyTopTracksPlaylist extends AbsSmartPlaylist {
 
-    public MyTopTracksPlaylist(Context context) {
+    public MyTopTracksPlaylist(@NonNull Context context) {
         super(context.getString(R.string.my_top_tracks), R.drawable.ic_trending_up_white_24dp);
     }
 
+    @NonNull
     @Override
-    public ArrayList<Song> getSongs(Context context) {
+    public ArrayList<Song> getSongs(@NonNull Context context) {
         return TopAndRecentlyPlayedTracksLoader.getTopTracks(context);
     }
 
     @Override
-    public void clear(Context context) {
+    public void clear(@NonNull Context context) {
         SongPlayCountStore.getInstance(context).clear();
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }

app/src/main/java/com/kabouzeid/gramophone/model/smartplaylist/RecentlyPlayedPlaylist.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.model.smartplaylist;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 
 import com.kabouzeid.gramophone.App;
 import com.kabouzeid.gramophone.R;
@@ -16,17 +17,18 @@ import java.util.ArrayList;
  */
 public class RecentlyPlayedPlaylist extends AbsSmartPlaylist {
 
-    public RecentlyPlayedPlaylist(Context context) {
+    public RecentlyPlayedPlaylist(@NonNull Context context) {
         super(context.getString(R.string.recently_played), R.drawable.ic_access_time_white_24dp);
     }
 
+    @NonNull
     @Override
-    public ArrayList<Song> getSongs(Context context) {
+    public ArrayList<Song> getSongs(@NonNull Context context) {
         return TopAndRecentlyPlayedTracksLoader.getRecentlyPlayedTracks(context);
     }
 
     @Override
-    public void clear(Context context) {
+    public void clear(@NonNull Context context) {
         RecentlyPlayedStore.getInstance(context).clear();
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }

app/src/main/java/com/kabouzeid/gramophone/prefs/ColorChooserPreference.java

@@ -15,15 +15,15 @@ public class ColorChooserPreference extends Preference {
     private int color;
     private int border;
 
-    public ColorChooserPreference(Context context, AttributeSet attrs) {
+    public ColorChooserPreference(@NonNull Context context, @NonNull AttributeSet attrs) {
         this(context, attrs, 0);
     }
 
-    public ColorChooserPreference(Context context) {
+    public ColorChooserPreference(@NonNull Context context) {
         this(context, null, 0);
     }
 
-    public ColorChooserPreference(Context context, AttributeSet attrs, int defStyleAttr) {
+    public ColorChooserPreference(@NonNull Context context, @NonNull AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         setLayoutResource(R.layout.preference_custom);
         setWidgetLayoutResource(R.layout.preference_color_widget);

app/src/main/java/com/kabouzeid/gramophone/prefs/DynamicPreferenceCategory.java

@@ -17,15 +17,15 @@ import com.kabouzeid.gramophone.R;
  */
 public class DynamicPreferenceCategory extends PreferenceCategory {
 
-    public DynamicPreferenceCategory(Context context, AttributeSet attrs) {
+    public DynamicPreferenceCategory(@NonNull Context context, @NonNull AttributeSet attrs) {
         this(context, attrs, 0);
     }
 
-    public DynamicPreferenceCategory(Context context) {
+    public DynamicPreferenceCategory(@NonNull Context context) {
         this(context, null, 0);
     }
 
-    public DynamicPreferenceCategory(Context context, AttributeSet attrs, int defStyleAttr) {
+    public DynamicPreferenceCategory(@NonNull Context context, @NonNull AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         setLayoutResource(R.layout.preference_category_custom);
         setSelectable(false);

app/src/main/java/com/kabouzeid/gramophone/provider/AlbumJSONStore.java

@@ -5,25 +5,29 @@ import android.content.Context;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 public class AlbumJSONStore extends SQLiteOpenHelper {
 
     public static final String DATABASE_NAME = "albums_last_fm.db";
     private static final int VERSION = 1;
+    @Nullable
     private static AlbumJSONStore sInstance = null;
 
     public AlbumJSONStore(final Context context) {
         super(context, DATABASE_NAME, null, VERSION);
     }
 
-    public static synchronized AlbumJSONStore getInstance(final Context context) {
+    @Nullable
+    public static synchronized AlbumJSONStore getInstance(@NonNull final Context context) {
         if (sInstance == null) {
             sInstance = new AlbumJSONStore(context.getApplicationContext());
         }
         return sInstance;
     }
 
-    public void addAlbumJSON(final String albumAndArtistName, final String json) {
+    public void addAlbumJSON(@Nullable final String albumAndArtistName, @Nullable final String json) {
         if (albumAndArtistName == null || json == null) {
             return;
         }
@@ -41,7 +45,8 @@ public class AlbumJSONStore extends SQLiteOpenHelper {
         database.endTransaction();
     }
 
-    public String getJSONData(final String albumAndArtistName) {
+    @Nullable
+    public String getJSONData(@Nullable final String albumAndArtistName) {
         if (albumAndArtistName == null) {
             return null;
         }
@@ -68,7 +73,7 @@ public class AlbumJSONStore extends SQLiteOpenHelper {
         return null;
     }
 
-    public void removeAlbumJSON(final String albumAndArtistName) {
+    public void removeAlbumJSON(@NonNull final String albumAndArtistName) {
         final SQLiteDatabase database = getReadableDatabase();
         database.delete(AlbumJSONColumns.NAME, AlbumJSONColumns.ALBUM_PLUS_ARTIST_NAME + " = ?", new String[]{
                 albumAndArtistName.trim().toLowerCase()
@@ -83,7 +88,7 @@ public class AlbumJSONStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onCreate(final SQLiteDatabase db) {
+    public void onCreate(@NonNull final SQLiteDatabase db) {
         db.execSQL("CREATE TABLE IF NOT EXISTS " + AlbumJSONColumns.NAME +
                         " (" + AlbumJSONColumns.ALBUM_PLUS_ARTIST_NAME + " TEXT NOT NULL," +
                         AlbumJSONColumns.JSON_DATA + " TEXT NOT NULL);"
@@ -92,7 +97,7 @@ public class AlbumJSONStore extends SQLiteOpenHelper {
 
 
     @Override
-    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {
+    public void onUpgrade(@NonNull final SQLiteDatabase db, final int oldVersion, final int newVersion) {
         db.execSQL("DROP TABLE IF EXISTS " + AlbumJSONColumns.NAME);
         onCreate(db);
     }

app/src/main/java/com/kabouzeid/gramophone/provider/ArtistJSONStore.java

@@ -5,25 +5,29 @@ import android.content.Context;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 public class ArtistJSONStore extends SQLiteOpenHelper {
 
     public static final String DATABASE_NAME = "artists_last_fm.db";
     private static final int VERSION = 1;
+    @Nullable
     private static ArtistJSONStore sInstance = null;
 
     public ArtistJSONStore(final Context context) {
         super(context, DATABASE_NAME, null, VERSION);
     }
 
-    public static synchronized ArtistJSONStore getInstance(final Context context) {
+    @Nullable
+    public static synchronized ArtistJSONStore getInstance(@NonNull final Context context) {
         if (sInstance == null) {
             sInstance = new ArtistJSONStore(context.getApplicationContext());
         }
         return sInstance;
     }
 
-    public void addArtistJSON(final String artistName, final String json) {
+    public void addArtistJSON(@Nullable final String artistName, @Nullable final String json) {
         if (artistName == null || json == null) {
             return;
         }
@@ -41,7 +45,8 @@ public class ArtistJSONStore extends SQLiteOpenHelper {
         database.endTransaction();
     }
 
-    public String getArtistJSON(final String artistName) {
+    @Nullable
+    public String getArtistJSON(@Nullable final String artistName) {
         if (artistName == null) {
             return null;
         }
@@ -68,7 +73,7 @@ public class ArtistJSONStore extends SQLiteOpenHelper {
         return null;
     }
 
-    public void removeArtistJSON(final String artistName) {
+    public void removeArtistJSON(@NonNull final String artistName) {
         final SQLiteDatabase database = getReadableDatabase();
         database.delete(ArtistJSONColumns.NAME, ArtistJSONColumns.ARTIST_NAME + "=?", new String[]{
                 artistName.trim().toLowerCase()
@@ -83,7 +88,7 @@ public class ArtistJSONStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onCreate(final SQLiteDatabase db) {
+    public void onCreate(@NonNull final SQLiteDatabase db) {
         db.execSQL("CREATE TABLE IF NOT EXISTS " + ArtistJSONColumns.NAME +
                         " (" + ArtistJSONColumns.ARTIST_NAME + " TEXT NOT NULL," +
                         ArtistJSONColumns.JSON_DATA + " TEXT NOT NULL);"
@@ -92,7 +97,7 @@ public class ArtistJSONStore extends SQLiteOpenHelper {
 
 
     @Override
-    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {
+    public void onUpgrade(@NonNull final SQLiteDatabase db, final int oldVersion, final int newVersion) {
         db.execSQL("DROP TABLE IF EXISTS " + ArtistJSONColumns.NAME);
         onCreate(db);
     }

app/src/main/java/com/kabouzeid/gramophone/provider/MusicPlaybackQueueStore.java

@@ -22,6 +22,8 @@ import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
 import android.provider.BaseColumns;
 import android.provider.MediaStore.Audio.AudioColumns;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.loader.SongLoader;
 import com.kabouzeid.gramophone.model.Song;
@@ -34,6 +36,7 @@ import java.util.ArrayList;
  *         This keeps track of the music playback and history state of the playback service
  */
 public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
+    @Nullable
     private static MusicPlaybackQueueStore sInstance = null;
     public static final String DATABASE_NAME = "music_playback_state.db";
     public static final String PLAYING_QUEUE_TABLE_NAME = "playing_queue";
@@ -50,12 +53,12 @@ public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onCreate(final SQLiteDatabase db) {
+    public void onCreate(@NonNull final SQLiteDatabase db) {
         createTable(db, PLAYING_QUEUE_TABLE_NAME);
         createTable(db, ORIGINAL_PLAYING_QUEUE_TABLE_NAME);
     }
 
-    private void createTable(final SQLiteDatabase db, final String tableName) {
+    private void createTable(@NonNull final SQLiteDatabase db, final String tableName) {
         //noinspection StringBufferReplaceableByString
         StringBuilder builder = new StringBuilder();
         builder.append("CREATE TABLE IF NOT EXISTS ");
@@ -93,7 +96,7 @@ public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {
+    public void onUpgrade(@NonNull final SQLiteDatabase db, final int oldVersion, final int newVersion) {
         // not necessary yet
         db.execSQL("DROP TABLE IF EXISTS " + PLAYING_QUEUE_TABLE_NAME);
         db.execSQL("DROP TABLE IF EXISTS " + ORIGINAL_PLAYING_QUEUE_TABLE_NAME);
@@ -101,7 +104,7 @@ public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+    public void onDowngrade(@NonNull SQLiteDatabase db, int oldVersion, int newVersion) {
         // If we ever have downgrade, drop the table to be safe
         db.execSQL("DROP TABLE IF EXISTS " + PLAYING_QUEUE_TABLE_NAME);
         db.execSQL("DROP TABLE IF EXISTS " + ORIGINAL_PLAYING_QUEUE_TABLE_NAME);
@@ -112,14 +115,15 @@ public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
      * @param context The {@link Context} to use
      * @return A new instance of this class.
      */
-    public static synchronized MusicPlaybackQueueStore getInstance(final Context context) {
+    @Nullable
+    public static synchronized MusicPlaybackQueueStore getInstance(@NonNull final Context context) {
         if (sInstance == null) {
             sInstance = new MusicPlaybackQueueStore(context.getApplicationContext());
         }
         return sInstance;
     }
 
-    public synchronized void saveQueues(final ArrayList<Song> playingQueue, final ArrayList<Song> originalPlayingQueue) {
+    public synchronized void saveQueues(@NonNull final ArrayList<Song> playingQueue, @NonNull final ArrayList<Song> originalPlayingQueue) {
         saveQueue(PLAYING_QUEUE_TABLE_NAME, playingQueue);
         saveQueue(ORIGINAL_PLAYING_QUEUE_TABLE_NAME, originalPlayingQueue);
     }
@@ -130,7 +134,7 @@ public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
      *
      * @param queue the queue to save
      */
-    private synchronized void saveQueue(final String tableName, final ArrayList<Song> queue) {
+    private synchronized void saveQueue(final String tableName, @NonNull final ArrayList<Song> queue) {
         final SQLiteDatabase database = getWritableDatabase();
         database.beginTransaction();
 
@@ -170,15 +174,18 @@ public class MusicPlaybackQueueStore extends SQLiteOpenHelper {
         }
     }
 
+    @NonNull
     public ArrayList<Song> getSavedPlayingQueue() {
         return getQueue(PLAYING_QUEUE_TABLE_NAME);
     }
 
+    @NonNull
     public ArrayList<Song> getSavedOriginalPlayingQueue() {
         return getQueue(ORIGINAL_PLAYING_QUEUE_TABLE_NAME);
     }
 
-    private ArrayList<Song> getQueue(final String tableName) {
+    @NonNull
+    private ArrayList<Song> getQueue(@NonNull final String tableName) {
         Cursor cursor = getReadableDatabase().query(tableName, null,
                 null, null, null, null, null);
         return SongLoader.getSongs(cursor);

app/src/main/java/com/kabouzeid/gramophone/provider/RecentlyPlayedStore.java

@@ -21,12 +21,15 @@ import android.content.Context;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 public class RecentlyPlayedStore extends SQLiteOpenHelper {
     private static final int MAX_ITEMS_IN_DB = 100;
 
     public static final String DATABASE_NAME = "recently_played.db";
     private static final int VERSION = 1;
+    @Nullable
     private static RecentlyPlayedStore sInstance = null;
 
     public RecentlyPlayedStore(final Context context) {
@@ -34,25 +37,26 @@ public class RecentlyPlayedStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onCreate(final SQLiteDatabase db) {
+    public void onCreate(@NonNull final SQLiteDatabase db) {
         db.execSQL("CREATE TABLE IF NOT EXISTS " + RecentStoreColumns.NAME + " ("
                 + RecentStoreColumns.ID + " LONG NOT NULL," + RecentStoreColumns.TIME_PLAYED
                 + " LONG NOT NULL);");
     }
 
     @Override
-    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+    public void onUpgrade(@NonNull SQLiteDatabase db, int oldVersion, int newVersion) {
         db.execSQL("DROP TABLE IF EXISTS " + RecentStoreColumns.NAME);
         onCreate(db);
     }
 
     @Override
-    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+    public void onDowngrade(@NonNull SQLiteDatabase db, int oldVersion, int newVersion) {
         db.execSQL("DROP TABLE IF EXISTS " + RecentStoreColumns.NAME);
         onCreate(db);
     }
 
-    public static synchronized RecentlyPlayedStore getInstance(final Context context) {
+    @Nullable
+    public static synchronized RecentlyPlayedStore getInstance(@NonNull final Context context) {
         if (sInstance == null) {
             sInstance = new RecentlyPlayedStore(context.getApplicationContext());
         }

app/src/main/java/com/kabouzeid/gramophone/provider/SongPlayCountStore.java

@@ -21,6 +21,8 @@ import android.content.Context;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.view.animation.AccelerateInterpolator;
 import android.view.animation.Interpolator;
 
@@ -29,12 +31,14 @@ import android.view.animation.Interpolator;
  * the top played tracks as well as the playlist images
  */
 public class SongPlayCountStore extends SQLiteOpenHelper {
+    @Nullable
     private static SongPlayCountStore sInstance = null;
 
     public static final String DATABASE_NAME = "song_play_count.db";
     private static final int VERSION = 1;
 
     // interpolator curve applied for measuring the curve
+    @NonNull
     private static Interpolator sInterpolator = new AccelerateInterpolator(1.5f);
 
     // how many weeks worth of playback to track
@@ -51,6 +55,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
     @SuppressWarnings("FieldCanBeLocal")
     private static int ONE_WEEK_IN_MS = 1000 * 60 * 60 * 24 * 7;
 
+    @NonNull
     private static String WHERE_ID_EQUALS = SongPlayCountColumns.ID + "=?";
 
     // number of weeks since epoch time
@@ -69,7 +74,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onCreate(final SQLiteDatabase db) {
+    public void onCreate(@NonNull final SQLiteDatabase db) {
         // create the play count table
         // WARNING: If you change the order of these columns
         // please update getColumnIndexForWeek
@@ -95,13 +100,13 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
     }
 
     @Override
-    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) {
+    public void onUpgrade(@NonNull final SQLiteDatabase db, final int oldVersion, final int newVersion) {
         db.execSQL("DROP TABLE IF EXISTS " + SongPlayCountColumns.NAME);
         onCreate(db);
     }
 
     @Override
-    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+    public void onDowngrade(@NonNull SQLiteDatabase db, int oldVersion, int newVersion) {
         // If we ever have downgrade, drop the table to be safe
         db.execSQL("DROP TABLE IF EXISTS " + SongPlayCountColumns.NAME);
         onCreate(db);
@@ -111,7 +116,8 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
      * @param context The {@link Context} to use
      * @return A new instance of this class.
      */
-    public static synchronized SongPlayCountStore getInstance(final Context context) {
+    @Nullable
+    public static synchronized SongPlayCountStore getInstance(@NonNull final Context context) {
         if (sInstance == null) {
             sInstance = new SongPlayCountStore(context.getApplicationContext());
         }
@@ -138,7 +144,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
      * @param database a write able database
      * @param songId   the id of the track
      */
-    private void createNewPlayedEntry(final SQLiteDatabase database, final long songId) {
+    private void createNewPlayedEntry(@NonNull final SQLiteDatabase database, final long songId) {
         // no row exists, create a new one
         float newScore = getScoreMultiplierForWeek(0);
         int newPlayCount = 1;
@@ -160,7 +166,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
      * @param id        the id of the track to bump
      * @param bumpCount whether to bump the current's week play count by 1 and adjust the score
      */
-    private void updateExistingRow(final SQLiteDatabase database, final long id, boolean bumpCount) {
+    private void updateExistingRow(@NonNull final SQLiteDatabase database, final long id, boolean bumpCount) {
         String stringId = String.valueOf(id);
 
         // begin the transaction
@@ -329,7 +335,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
      * @param database database to use
      * @param stringId id to delete
      */
-    private void deleteEntry(final SQLiteDatabase database, final String stringId) {
+    private void deleteEntry(@NonNull final SQLiteDatabase database, final String stringId) {
         database.delete(SongPlayCountColumns.NAME, WHERE_ID_EQUALS, new String[]{stringId});
     }
 
@@ -340,7 +346,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
      *                   where playCounts[N] is the # of times it was played N weeks ago
      * @return the score
      */
-    private static float calculateScore(final int[] playCounts) {
+    private static float calculateScore(@Nullable final int[] playCounts) {
         if (playCounts == null) {
             return 0;
         }
@@ -359,6 +365,7 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
      * @param week number
      * @return the column name
      */
+    @NonNull
     private static String getColumnNameForWeek(final int week) {
         return SongPlayCountColumns.WEEK_PLAY_COUNT + String.valueOf(week);
     }

app/src/main/java/com/kabouzeid/gramophone/service/MediaButtonIntentReceiver.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.service;
 import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
+import android.support.annotation.NonNull;
 import android.view.KeyEvent;
 
 public class MediaButtonIntentReceiver extends BroadcastReceiver {
@@ -12,7 +13,7 @@ public class MediaButtonIntentReceiver extends BroadcastReceiver {
     private static long mLastClickTime = 0;
 
     @Override
-    public void onReceive(Context context, Intent intent) {
+    public void onReceive(@NonNull Context context, @NonNull Intent intent) {
         if (intent.getAction().equals(Intent.ACTION_MEDIA_BUTTON)) {
             final KeyEvent event = intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
             if (event == null)

app/src/main/java/com/kabouzeid/gramophone/service/MultiPlayer.java

@@ -7,6 +7,8 @@ import android.media.audiofx.AudioEffect;
 import android.net.Uri;
 import android.os.Handler;
 import android.os.PowerManager;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.util.Log;
 import android.widget.Toast;
 
@@ -22,9 +24,12 @@ public class MultiPlayer implements MediaPlayer.OnErrorListener,
         MediaPlayer.OnCompletionListener {
     public static final String TAG = MultiPlayer.class.getSimpleName();
 
+    @NonNull
     private final WeakReference<MusicService> mService;
 
+    @Nullable
     private MediaPlayer mCurrentMediaPlayer = new MediaPlayer();
+    @Nullable
     private MediaPlayer mNextMediaPlayer;
 
     private Handler mHandler;
@@ -45,7 +50,7 @@ public class MultiPlayer implements MediaPlayer.OnErrorListener,
      * @return True if the <code>player</code> has been prepared and is
      * ready to play, false otherwise
      */
-    public boolean setDataSource(final String path) {
+    public boolean setDataSource(@NonNull final String path) {
         mIsInitialized = false;
         mIsInitialized = setDataSourceImpl(mCurrentMediaPlayer, path);
         if (mIsInitialized) {
@@ -61,7 +66,7 @@ public class MultiPlayer implements MediaPlayer.OnErrorListener,
      * @return True if the <code>player</code> has been prepared and is
      * ready to play, false otherwise
      */
-    private boolean setDataSourceImpl(final MediaPlayer player, final String path) {
+    private boolean setDataSourceImpl(@NonNull final MediaPlayer player, @NonNull final String path) {
         MusicService service = mService.get();
         if (service == null) {
             return false;
@@ -95,7 +100,7 @@ public class MultiPlayer implements MediaPlayer.OnErrorListener,
      * @param path The path of the file, or the http/rtsp URL of the stream
      *             you want to play
      */
-    public void setNextDataSource(final String path) {
+    public void setNextDataSource(@Nullable final String path) {
         MusicService service = mService.get();
         if (service == null) {
             return;
@@ -122,7 +127,7 @@ public class MultiPlayer implements MediaPlayer.OnErrorListener,
             if (setDataSourceImpl(mNextMediaPlayer, path)) {
                 try {
                     mCurrentMediaPlayer.setNextMediaPlayer(mNextMediaPlayer);
-                } catch (IllegalArgumentException | IllegalStateException e) {
+                } catch (@NonNull IllegalArgumentException | IllegalStateException e) {
                     Log.e(TAG, "setNextDataSource: setNextMediaPlayer()", e);
                     if (mNextMediaPlayer != null) {
                         mNextMediaPlayer.release();
@@ -269,7 +274,7 @@ public class MultiPlayer implements MediaPlayer.OnErrorListener,
         try {
             mCurrentMediaPlayer.setAudioSessionId(sessionId);
             return true;
-        } catch (IllegalArgumentException | IllegalStateException e) {
+        } catch (@NonNull IllegalArgumentException | IllegalStateException e) {
             return false;
         }
     }

app/src/main/java/com/kabouzeid/gramophone/service/MusicService.java

@@ -23,6 +23,8 @@ import android.os.Message;
 import android.os.PowerManager;
 import android.os.Process;
 import android.preference.PreferenceManager;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.view.View;
 import android.widget.Toast;
 
@@ -95,8 +97,11 @@ public class MusicService extends Service {
 
     private final IBinder musicBind = new MusicBinder();
 
+    @Nullable
     private MultiPlayer player;
+    @Nullable
     private ArrayList<Song> playingQueue;
+    @Nullable
     private ArrayList<Song> originalPlayingQueue;
     private int position = -1;
     private int nextPosition = -1;
@@ -113,14 +118,16 @@ public class MusicService extends Service {
     private QueueSaveHandler queueSaveHandler;
     private HandlerThread musicPlayerHandlerThread;
     private HandlerThread queueSaveHandlerThread;
+    @Nullable
     private RecentlyPlayedStore recentlyPlayedStore;
+    @Nullable
     private SongPlayCountStore songPlayCountStore;
     private boolean notNotifiedMetaChangedForCurrentTrack;
     private boolean isServiceInUse;
 
     private final BroadcastReceiver becomingNoisyReceiver = new BroadcastReceiver() {
         @Override
-        public void onReceive(Context context, Intent intent) {
+        public void onReceive(Context context, @NonNull Intent intent) {
             if (intent.getAction().equals(AudioManager.ACTION_AUDIO_BECOMING_NOISY)) {
                 pause();
             }
@@ -129,7 +136,7 @@ public class MusicService extends Service {
 
     private final BroadcastReceiver preferencesChangedReceiver = new BroadcastReceiver() {
         @Override
-        public void onReceive(Context context, Intent intent) {
+        public void onReceive(Context context, @NonNull Intent intent) {
             switch (intent.getAction()) {
                 case SETTING_GAPLESS_PLAYBACK_CHANGED:
                     setGaplessPlaybackEnabled(intent.getBooleanExtra(SETTING_BOOLEAN_EXTRA, false));
@@ -225,7 +232,7 @@ public class MusicService extends Service {
     }
 
     @Override
-    public int onStartCommand(Intent intent, int flags, int startId) {
+    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
         if (intent != null) {
             if (intent.getAction() != null) {
                 String action = intent.getAction();
@@ -438,7 +445,7 @@ public class MusicService extends Service {
             final String currentAlbumArtUri = MusicUtil.getSongImageLoaderString(song);
             ImageLoader.getInstance().displayImage(currentAlbumArtUri, new NonViewAware(new ImageSize(-1, -1), ViewScaleType.CROP), new SimpleImageLoadingListener() {
                 @Override
-                public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
+                public void onLoadingComplete(String imageUri, View view, @Nullable Bitmap loadedImage) {
                     if (currentAlbumArtUri.equals(imageUri)) {
                         if (loadedImage != null) {
                             // RemoteControlClient wants to recycle the bitmaps thrown at it, so we need
@@ -495,7 +502,7 @@ public class MusicService extends Service {
         WidgetMedium.updateWidgets(this, getCurrentSong(), isPlaying());
     }
 
-    private static String getTrackUri(Song song) {
+    private static String getTrackUri(@NonNull Song song) {
         return ContentUris.withAppendedId(android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, song.id).toString();
     }
 
@@ -530,6 +537,7 @@ public class MusicService extends Service {
         return getPosition() == getPlayingQueue().size() - 1;
     }
 
+    @Nullable
     public ArrayList<Song> getPlayingQueue() {
         return playingQueue;
     }
@@ -553,7 +561,7 @@ public class MusicService extends Service {
         }
     }
 
-    public void openAndPlayQueue(final ArrayList<Song> playingQueue, final int startPosition, final boolean startPlaying) {
+    public void openAndPlayQueue(@Nullable final ArrayList<Song> playingQueue, final int startPosition, final boolean startPlaying) {
         if (playingQueue != null && !playingQueue.isEmpty() && startPosition >= 0 && startPosition < playingQueue.size()) {
             originalPlayingQueue = playingQueue;
             this.playingQueue = new ArrayList<>(originalPlayingQueue);
@@ -618,7 +626,7 @@ public class MusicService extends Service {
         saveState();
     }
 
-    public void removeSong(Song song) {
+    public void removeSong(@NonNull Song song) {
         for (int i = 0; i < playingQueue.size(); i++) {
             if (playingQueue.get(i).id == song.id) playingQueue.remove(i);
         }
@@ -796,7 +804,7 @@ public class MusicService extends Service {
         notifyChange(SHUFFLE_MODE_CHANGED);
     }
 
-    private void notifyChange(final String what) {
+    private void notifyChange(@NonNull final String what) {
         final Intent internalIntent = new Intent(what);
 
         final Song currentSong = getCurrentSong();
@@ -857,21 +865,23 @@ public class MusicService extends Service {
     }
 
     public class MusicBinder extends Binder {
+        @NonNull
         public MusicService getService() {
             return MusicService.this;
         }
     }
 
     private static final class QueueSaveHandler extends Handler {
+        @NonNull
         private final WeakReference<MusicService> mService;
 
-        public QueueSaveHandler(final MusicService service, final Looper looper) {
+        public QueueSaveHandler(final MusicService service, @NonNull final Looper looper) {
             super(looper);
             mService = new WeakReference<>(service);
         }
 
         @Override
-        public void handleMessage(Message msg) {
+        public void handleMessage(@NonNull Message msg) {
             final MusicService service = mService.get();
             switch (msg.what) {
                 case SAVE_QUEUES:
@@ -882,16 +892,17 @@ public class MusicService extends Service {
     }
 
     private static final class MusicPlayerHandler extends Handler {
+        @NonNull
         private final WeakReference<MusicService> mService;
         private float currentDuckVolume = 1.0f;
 
-        public MusicPlayerHandler(final MusicService service, final Looper looper) {
+        public MusicPlayerHandler(final MusicService service, @NonNull final Looper looper) {
             super(looper);
             mService = new WeakReference<>(service);
         }
 
         @Override
-        public void handleMessage(final Message msg) {
+        public void handleMessage(@NonNull final Message msg) {
             final MusicService service = mService.get();
             if (service == null) {
                 return;

app/src/main/java/com/kabouzeid/gramophone/ui/activities/AlbumDetailActivity.java

@@ -8,6 +8,8 @@ import android.graphics.BitmapFactory;
 import android.graphics.Color;
 import android.os.Build;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.util.Pair;
 import android.support.v7.graphics.Palette;
 import android.support.v7.widget.GridLayoutManager;
@@ -181,6 +183,7 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
         }
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -226,7 +229,7 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
 
 
                     @Override
-                    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
+                    public void onLoadingComplete(String imageUri, View view, @NonNull Bitmap loadedImage) {
                         applyPalette(loadedImage);
                         albumArtBackground.setImageBitmap(new StackBlurManager(loadedImage).process(10));
                         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
@@ -236,13 +239,13 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
         );
     }
 
-    private void applyPalette(Bitmap bitmap) {
+    private void applyPalette(@Nullable Bitmap bitmap) {
         if (bitmap != null) {
             Palette.from(bitmap)
                     .resizeBitmapSize(100)
                     .generate(new Palette.PaletteAsyncListener() {
                         @Override
-                        public void onGenerated(Palette palette) {
+                        public void onGenerated(@NonNull Palette palette) {
                             final Palette.Swatch vibrantSwatch = palette.getVibrantSwatch();
                             if (vibrantSwatch != null) {
                                 toolbarColor = vibrantSwatch.getRgb();
@@ -345,7 +348,7 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         int id = item.getItemId();
         switch (id) {
             case R.id.action_sleep_timer:
@@ -389,7 +392,7 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.SONGS_CHANGED:
             case DataBaseChangedEvent.ALBUMS_CHANGED:
@@ -402,7 +405,7 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
     }
 
     @Subscribe
-    public void onUIPreferenceChanged(UIPreferenceChangedEvent event) {
+    public void onUIPreferenceChanged(@NonNull UIPreferenceChangedEvent event) {
         switch (event.getAction()) {
             case UIPreferenceChangedEvent.COLORED_NAVIGATION_BAR_ALBUM_CHANGED:
                 setNavigationBarColored((boolean) event.getValue());
@@ -417,7 +420,7 @@ public class AlbumDetailActivity extends AbsFabActivity implements PaletteColorH
     }
 
     @Override
-    public MaterialCab openCab(int menuRes, final MaterialCab.Callback callback) {
+    public MaterialCab openCab(int menuRes, @NonNull final MaterialCab.Callback callback) {
         if (cab != null && cab.isActive()) cab.finish();
         cab = new MaterialCab(this, R.id.cab_stub)
                 .setMenu(menuRes)

app/src/main/java/com/kabouzeid/gramophone/ui/activities/ArtistDetailActivity.java

@@ -8,6 +8,8 @@ import android.graphics.BitmapFactory;
 import android.graphics.Color;
 import android.os.Build;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.graphics.Palette;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
@@ -109,6 +111,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
     private int bottomOffset;
 
     private Artist artist;
+    @Nullable
     private Spanned biography;
     private ArtistAlbumAdapter albumAdapter;
     private ArtistSongAdapter songAdapter;
@@ -219,6 +222,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
         albumRecyclerView = ButterKnife.findById(songListHeader, R.id.recycler_view);
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -276,7 +280,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
     private void loadBiography() {
         lastFMRestClient.getApiService().getArtistInfo(artist.name, null, new Callback<ArtistInfo>() {
             @Override
-            public void success(ArtistInfo artistInfo, Response response) {
+            public void success(@NonNull ArtistInfo artistInfo, Response response) {
                 if (artistInfo.getArtist() != null) {
                     String bio = artistInfo.getArtist().getBio().getContent();
                     if (bio != null && !bio.trim().equals("")) {
@@ -315,7 +319,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
         }
         lastFMRestClient.getApiService().getArtistInfo(artist.name, forceDownload ? "no-cache" : null, new Callback<ArtistInfo>() {
             @Override
-            public void success(ArtistInfo artistInfo, Response response) {
+            public void success(@NonNull ArtistInfo artistInfo, Response response) {
                 if (artistInfo.getArtist() != null) {
                     List<Image> images = artistInfo.getArtist().getImage();
                     int lastElementIndex = images.size() - 1;
@@ -336,7 +340,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
                                 }
 
                                 @Override
-                                public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
+                                public void onLoadingComplete(String imageUri, View view, @Nullable Bitmap loadedImage) {
                                     if (loadedImage != null) {
                                         applyPalette(loadedImage);
                                         artistImageBackground.setImageBitmap(new StackBlurManager(loadedImage).process(10));
@@ -373,14 +377,14 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
         artistImageBackground.setImageBitmap(defaultArtistImageBlurManager.process(10));
     }
 
-    private void applyPalette(Bitmap bitmap) {
+    private void applyPalette(@Nullable Bitmap bitmap) {
         if (bitmap != null) {
             Palette.from(bitmap)
                     .resizeBitmapSize(100)
                     .generate(new Palette.PaletteAsyncListener() {
 
                         @Override
-                        public void onGenerated(Palette palette) {
+                        public void onGenerated(@NonNull Palette palette) {
                             final Palette.Swatch vibrantSwatch = palette.getVibrantSwatch();
                             if (vibrantSwatch != null) {
                                 toolbarColor = vibrantSwatch.getRgb();
@@ -447,7 +451,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         int id = item.getItemId();
         switch (id) {
             case R.id.action_sleep_timer:
@@ -531,7 +535,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.SONGS_CHANGED:
             case DataBaseChangedEvent.ALBUMS_CHANGED:
@@ -547,7 +551,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
     }
 
     @Subscribe
-    public void onUIPreferenceChanged(UIPreferenceChangedEvent event) {
+    public void onUIPreferenceChanged(@NonNull UIPreferenceChangedEvent event) {
         switch (event.getAction()) {
             case UIPreferenceChangedEvent.COLORED_NAVIGATION_BAR_ARTIST_CHANGED:
                 setNavigationBarColored((boolean) event.getValue());
@@ -562,7 +566,7 @@ public class ArtistDetailActivity extends AbsFabActivity implements PaletteColor
     }
 
     @Override
-    public MaterialCab openCab(int menuRes, final MaterialCab.Callback callback) {
+    public MaterialCab openCab(int menuRes, @NonNull final MaterialCab.Callback callback) {
         if (cab != null && cab.isActive()) cab.finish();
         cab = new MaterialCab(this, R.id.cab_stub)
                 .setMenu(menuRes)

app/src/main/java/com/kabouzeid/gramophone/ui/activities/MainActivity.java

@@ -9,6 +9,7 @@ import android.os.Bundle;
 import android.os.Handler;
 import android.provider.MediaStore;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.AppBarLayout;
 import android.support.design.widget.AppBarLayout.OnOffsetChangedListener;
 import android.support.design.widget.NavigationView;
@@ -87,6 +88,7 @@ public class MainActivity extends AbsFabActivity
     private PagerAdapter pagerAdapter;
     private int currentPage = -1;
     private MaterialCab cab;
+    @Nullable
     private View navigationDrawerHeader;
 
     @Override
@@ -180,7 +182,7 @@ public class MainActivity extends AbsFabActivity
         ));
         navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
             @Override
-            public boolean onNavigationItemSelected(MenuItem menuItem) {
+            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                 drawerLayout.closeDrawers();
                 switch (menuItem.getItemId()) {
                     case R.id.nav_songs:
@@ -242,6 +244,7 @@ public class MainActivity extends AbsFabActivity
         setUpNavigationView();
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -307,7 +310,7 @@ public class MainActivity extends AbsFabActivity
     }
 
     @Override
-    public boolean onCreateOptionsMenu(Menu menu) {
+    public boolean onCreateOptionsMenu(@NonNull Menu menu) {
         if (isAlbumPage()) {
             getMenuInflater().inflate(R.menu.menu_albums, menu);
             setUpGridMenu(menu);
@@ -329,7 +332,7 @@ public class MainActivity extends AbsFabActivity
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         if (drawerToggle.onOptionsItemSelected(item)) {
             return true;
         }
@@ -370,7 +373,7 @@ public class MainActivity extends AbsFabActivity
     }
 
     @Override
-    public void onUIPreferenceChangedEvent(UIPreferenceChangedEvent event) {
+    public void onUIPreferenceChangedEvent(@NonNull UIPreferenceChangedEvent event) {
         super.onUIPreferenceChangedEvent(event);
         switch (event.getAction()) {
             case UIPreferenceChangedEvent.COLORED_NAVIGATION_BAR_OTHER_SCREENS_CHANGED:
@@ -402,7 +405,7 @@ public class MainActivity extends AbsFabActivity
         PreferenceUtils.getInstance(MainActivity.this).setLastStartPage(currentPage);
     }
 
-    private void handlePlaybackIntent(Intent intent) {
+    private void handlePlaybackIntent(@Nullable Intent intent) {
         if (intent == null) {
             return;
         }
@@ -447,7 +450,7 @@ public class MainActivity extends AbsFabActivity
         }
     }
 
-    private long parseIdFromIntent(Intent intent, String longKey,
+    private long parseIdFromIntent(@NonNull Intent intent, String longKey,
                                    String stringKey) {
         long id = intent.getLongExtra(longKey, -1);
         if (id < 0) {
@@ -475,6 +478,7 @@ public class MainActivity extends AbsFabActivity
         return pager.getCurrentItem() == PagerAdapter.MusicFragments.ALBUM.ordinal();
     }
 
+    @NonNull
     public AlbumViewFragment getAlbumFragment() {
         return (AlbumViewFragment) pagerAdapter.getFragment(PagerAdapter.MusicFragments.ALBUM.ordinal());
     }
@@ -495,7 +499,7 @@ public class MainActivity extends AbsFabActivity
 //        return (PlaylistViewFragment) pagerAdapter.getFragment(PagerAdapter.MusicFragments.PLAYLIST.ordinal());
 //    }
 
-    private void setUpGridMenu(Menu menu) {
+    private void setUpGridMenu(@NonNull Menu menu) {
         boolean isPortrait = Util.isInPortraitMode(this);
         int columns = isPortrait ? PreferenceUtils.getInstance(this).getAlbumGridColumns() : PreferenceUtils.getInstance(this).getAlbumGridColumnsLand();
         String title = isPortrait ? getResources().getString(R.string.action_grid_columns) : getResources().getString(R.string.action_grid_columns_land);
@@ -507,7 +511,7 @@ public class MainActivity extends AbsFabActivity
         gridSizeMenu.getItem(columns - 1).setChecked(true);
     }
 
-    private boolean handleGridSize(MenuItem item) {
+    private boolean handleGridSize(@NonNull MenuItem item) {
         int size = -1;
 
         switch (item.getItemId()) {

app/src/main/java/com/kabouzeid/gramophone/ui/activities/MusicControllerActivity.java

@@ -14,6 +14,8 @@ import android.os.Handler;
 import android.os.HandlerThread;
 import android.os.Looper;
 import android.os.Message;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.graphics.Palette;
 import android.support.v7.widget.CardView;
 import android.support.v7.widget.Toolbar;
@@ -279,7 +281,7 @@ public class MusicControllerActivity extends AbsFabActivity {
         setUpProgressSlider();
     }
 
-    private void setTint(SeekBar seekBar, int color) {
+    private void setTint(@NonNull SeekBar seekBar, int color) {
         ColorStateList s1 = ColorStateList.valueOf(color);
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
             seekBar.setThumbTintList(s1);
@@ -380,6 +382,7 @@ public class MusicControllerActivity extends AbsFabActivity {
     }
 
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -443,7 +446,7 @@ public class MusicControllerActivity extends AbsFabActivity {
                     }
 
                     @Override
-                    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
+                    public void onLoadingComplete(String imageUri, View view, @NonNull Bitmap loadedImage) {
                         applyPalette(loadedImage);
                         albumArtBackground.setImageBitmap(new StackBlurManager(loadedImage).process(10));
                     }
@@ -451,13 +454,13 @@ public class MusicControllerActivity extends AbsFabActivity {
         );
     }
 
-    private void applyPalette(Bitmap bitmap) {
+    private void applyPalette(@Nullable Bitmap bitmap) {
         if (bitmap != null) {
             Palette.from(bitmap)
                     .resizeBitmapSize(100)
                     .generate(new Palette.PaletteAsyncListener() {
                         @Override
-                        public void onGenerated(Palette palette) {
+                        public void onGenerated(@NonNull Palette palette) {
                             final Palette.Swatch vibrantSwatch = palette.getVibrantSwatch();
                             if (vibrantSwatch != null) {
                                 final int swatchRgb = vibrantSwatch.getRgb();
@@ -616,7 +619,7 @@ public class MusicControllerActivity extends AbsFabActivity {
     }
 
     @Override
-    public boolean onCreateOptionsMenu(Menu menu) {
+    public boolean onCreateOptionsMenu(@NonNull Menu menu) {
         getMenuInflater().inflate(R.menu.menu_music_playing, menu);
         boolean isFavorite = MusicUtil.isFavorite(this, song);
         menu.findItem(R.id.action_toggle_favorite)
@@ -626,7 +629,7 @@ public class MusicControllerActivity extends AbsFabActivity {
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         int id = item.getItemId();
         switch (id) {
             case R.id.action_sleep_timer:
@@ -701,13 +704,13 @@ public class MusicControllerActivity extends AbsFabActivity {
     private static class MusicProgressViewsUpdateHandler extends Handler {
         private WeakReference<MusicControllerActivity> activityReference;
 
-        public MusicProgressViewsUpdateHandler(final MusicControllerActivity activity, final Looper looper) {
+        public MusicProgressViewsUpdateHandler(final MusicControllerActivity activity, @NonNull final Looper looper) {
             super(looper);
             activityReference = new WeakReference<>(activity);
         }
 
         @Override
-        public void handleMessage(Message msg) {
+        public void handleMessage(@NonNull Message msg) {
             super.handleMessage(msg);
             if (msg.what == CMD_UPDATE_PROGRESS_VIEWS) {
                 activityReference.get().updateProgressViews();

app/src/main/java/com/kabouzeid/gramophone/ui/activities/PlaylistDetailActivity.java

@@ -1,6 +1,8 @@
 package com.kabouzeid.gramophone.ui.activities;
 
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.Toolbar;
@@ -33,6 +35,7 @@ public class PlaylistDetailActivity extends AbsFabActivity implements CabHolder
 
     public static final String TAG = PlaylistDetailActivity.class.getSimpleName();
 
+    @NonNull
     public static String EXTRA_PLAYLIST = "extra_playlist";
 
     @InjectView(R.id.recycler_view)
@@ -42,8 +45,10 @@ public class PlaylistDetailActivity extends AbsFabActivity implements CabHolder
     @InjectView(android.R.id.empty)
     TextView empty;
 
+    @Nullable
     private Playlist playlist;
     private MaterialCab cab;
+    @Nullable
     private AbsPlaylistSongAdapter adapter;
 
     @Override
@@ -110,6 +115,7 @@ public class PlaylistDetailActivity extends AbsFabActivity implements CabHolder
         }
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -122,7 +128,7 @@ public class PlaylistDetailActivity extends AbsFabActivity implements CabHolder
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         int id = item.getItemId();
         switch (id) {
             case R.id.action_sleep_timer:
@@ -165,7 +171,7 @@ public class PlaylistDetailActivity extends AbsFabActivity implements CabHolder
     }
 
     @Subscribe
-    public void onDataBaseEvent(DataBaseChangedEvent event) {
+    public void onDataBaseEvent(@NonNull DataBaseChangedEvent event) {
         switch (event.getAction()) {
             case DataBaseChangedEvent.PLAYLISTS_CHANGED:
             case DataBaseChangedEvent.DATABASE_CHANGED:

app/src/main/java/com/kabouzeid/gramophone/ui/activities/SearchActivity.java

@@ -6,6 +6,7 @@ import android.graphics.Color;
 import android.graphics.PorterDuff;
 import android.graphics.drawable.Drawable;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 import android.support.v4.content.ContextCompat;
 import android.support.v4.view.MenuItemCompat;
 import android.support.v7.widget.LinearLayoutManager;
@@ -74,6 +75,7 @@ public class SearchActivity extends AbsBaseActivity {
         setStatusBarThemeColor();
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -92,7 +94,7 @@ public class SearchActivity extends AbsBaseActivity {
     }
 
     @Override
-    public boolean onCreateOptionsMenu(Menu menu) {
+    public boolean onCreateOptionsMenu(@NonNull Menu menu) {
         getMenuInflater().inflate(R.menu.menu_search, menu);
 
         final MenuItem search = menu.findItem(R.id.action_search);
@@ -111,7 +113,7 @@ public class SearchActivity extends AbsBaseActivity {
 
         searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
             @Override
-            public boolean onQueryTextSubmit(String query) {
+            public boolean onQueryTextSubmit(@NonNull String query) {
                 onQueryTextChange(query);
                 Util.hideSoftKeyboard(SearchActivity.this);
                 searchView.clearFocus();
@@ -119,7 +121,7 @@ public class SearchActivity extends AbsBaseActivity {
             }
 
             @Override
-            public boolean onQueryTextChange(String newText) {
+            public boolean onQueryTextChange(@NonNull String newText) {
                 search(newText);
                 return false;
             }
@@ -142,7 +144,7 @@ public class SearchActivity extends AbsBaseActivity {
         return true;
     }
 
-    private void search(String query) {
+    private void search(@NonNull String query) {
         if (searchAdapter != null) {
             searchAdapter.search(query);
             empty.setVisibility(searchAdapter.getItemCount() < 1 ? View.VISIBLE : View.GONE);

app/src/main/java/com/kabouzeid/gramophone/ui/activities/SettingsActivity.java

@@ -10,6 +10,8 @@ import android.preference.ListPreference;
 import android.preference.Preference;
 import android.preference.PreferenceFragment;
 import android.preference.PreferenceManager;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.widget.Toolbar;
 import android.view.MenuItem;
 
@@ -31,7 +33,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
     public static final String TAG = SettingsActivity.class.getSimpleName();
 
     @Override
-    protected void onCreate(Bundle savedInstanceState) {
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_preferences);
 
@@ -77,7 +79,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
             setSummary(defaultStartPage);
             defaultStartPage.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
                 @Override
-                public boolean onPreferenceChange(Preference preference, Object o) {
+                public boolean onPreferenceChange(Preference preference, @NonNull Object o) {
                     setSummary(defaultStartPage, o);
                     return true;
                 }
@@ -87,7 +89,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
             setSummary(generalTheme);
             generalTheme.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
                 @Override
-                public boolean onPreferenceChange(Preference preference, Object o) {
+                public boolean onPreferenceChange(Preference preference, @NonNull Object o) {
                     setSummary(generalTheme, o);
                     App.bus.post(new UIPreferenceChangedEvent(UIPreferenceChangedEvent.THEME_CHANGED, o));
                     return true;
@@ -99,7 +101,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
                     DialogUtils.resolveColor(getActivity(), android.R.attr.textColorPrimary));
             primaryColor.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
                 @Override
-                public boolean onPreferenceClick(Preference preference) {
+                public boolean onPreferenceClick(@NonNull Preference preference) {
                     new ColorChooserDialog().show(getActivity(), preference.getTitleRes(),
                             PreferenceUtils.getInstance(getActivity()).getThemeColorPrimary());
                     return true;
@@ -111,7 +113,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
                     DialogUtils.resolveColor(getActivity(), android.R.attr.textColorPrimary));
             accentColor.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
                 @Override
-                public boolean onPreferenceClick(Preference preference) {
+                public boolean onPreferenceClick(@NonNull Preference preference) {
                     new ColorChooserDialog().show(getActivity(), preference.getTitleRes(),
                             PreferenceUtils.getInstance(getActivity()).getThemeColorAccent());
                     return true;
@@ -178,13 +180,13 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
             });
         }
 
-        private static void setSummary(Preference preference) {
+        private static void setSummary(@NonNull Preference preference) {
             setSummary(preference, PreferenceManager
                     .getDefaultSharedPreferences(preference.getContext())
                     .getString(preference.getKey(), ""));
         }
 
-        private static void setSummary(Preference preference, Object value) {
+        private static void setSummary(Preference preference, @NonNull Object value) {
             String stringValue = value.toString();
 
             if (preference instanceof ListPreference) {
@@ -211,7 +213,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
     }
 
     @Override
-    protected void onUIPreferenceChangedEvent(UIPreferenceChangedEvent event) {
+    protected void onUIPreferenceChangedEvent(@NonNull UIPreferenceChangedEvent event) {
         super.onUIPreferenceChangedEvent(event);
         switch (event.getAction()) {
             case UIPreferenceChangedEvent.COLORED_NAVIGATION_BAR_OTHER_SCREENS_CHANGED:
@@ -231,7 +233,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         if (item.getItemId() == android.R.id.home) {
             onBackPressed();
             return true;
@@ -239,6 +241,7 @@ public class SettingsActivity extends AbsBaseActivity implements ColorChooserDia
         return super.onOptionsItemSelected(item);
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;

app/src/main/java/com/kabouzeid/gramophone/ui/activities/base/AbsBaseActivity.java

@@ -2,6 +2,7 @@ package com.kabouzeid.gramophone.ui.activities.base;
 
 import android.media.AudioManager;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 
 import com.crashlytics.android.Crashlytics;
 import com.kabouzeid.gramophone.App;
@@ -18,7 +19,7 @@ public abstract class AbsBaseActivity extends AbsThemeActivity implements KabVie
     private boolean areViewsEnabled;
     private final Object uiPreferenceChangeListener = new Object() {
         @Subscribe
-        public void onUIPreferenceChangedEvent(UIPreferenceChangedEvent event) {
+        public void onUIPreferenceChangedEvent(@NonNull UIPreferenceChangedEvent event) {
             AbsBaseActivity.this.onUIPreferenceChangedEvent(event);
         }
     };
@@ -34,6 +35,7 @@ public abstract class AbsBaseActivity extends AbsThemeActivity implements KabVie
         setVolumeControlStream(AudioManager.STREAM_MUSIC);
     }
 
+    @NonNull
     protected abstract String getTag();
 
     @Override
@@ -57,7 +59,7 @@ public abstract class AbsBaseActivity extends AbsThemeActivity implements KabVie
         return areViewsEnabled;
     }
 
-    protected void onUIPreferenceChangedEvent(UIPreferenceChangedEvent event) {
+    protected void onUIPreferenceChangedEvent(@NonNull UIPreferenceChangedEvent event) {
         switch (event.getAction()) {
             case UIPreferenceChangedEvent.THEME_CHANGED:
                 recreate();

app/src/main/java/com/kabouzeid/gramophone/ui/activities/base/AbsFabActivity.java

@@ -3,6 +3,8 @@ package com.kabouzeid.gramophone.ui.activities.base;
 import android.graphics.Color;
 import android.graphics.PorterDuff;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.FloatingActionButton;
 import android.support.v4.util.Pair;
 import android.util.Log;
@@ -30,6 +32,7 @@ import butterknife.Optional;
 public abstract class AbsFabActivity extends AbsPlaybackControlActivity {
     public static final String TAG = AbsFabActivity.class.getSimpleName();
 
+    @Nullable
     @Optional
     @InjectView(R.id.fab)
     FloatingActionButton fab;
@@ -83,7 +86,7 @@ public abstract class AbsFabActivity extends AbsPlaybackControlActivity {
 
         getFab().setOnTouchListener(new View.OnTouchListener() {
             @Override
-            public boolean onTouch(View view, MotionEvent event) {
+            public boolean onTouch(View view, @NonNull MotionEvent event) {
                 gestureDetector.onTouchEvent(event);
                 return false;
             }
@@ -119,6 +122,7 @@ public abstract class AbsFabActivity extends AbsPlaybackControlActivity {
         }
     }
 
+    @Nullable
     protected FloatingActionButton getFab() {
         if (fab == null) {
             fab = (FloatingActionButton) findViewById(R.id.fab);
@@ -136,7 +140,7 @@ public abstract class AbsFabActivity extends AbsPlaybackControlActivity {
         updateFabState();
     }
 
-    public Pair[] getSharedViewsWithFab(Pair[] sharedViews) {
+    public Pair[] getSharedViewsWithFab(@Nullable Pair[] sharedViews) {
         Pair[] sharedViewsWithFab;
         if (sharedViews != null) {
             sharedViewsWithFab = new Pair[sharedViews.length + 1];

app/src/main/java/com/kabouzeid/gramophone/ui/activities/base/AbsPlaybackControlActivity.java

@@ -8,6 +8,8 @@ import android.content.IntentFilter;
 import android.content.ServiceConnection;
 import android.os.Bundle;
 import android.os.IBinder;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.helper.MusicPlayerRemote;
 import com.kabouzeid.gramophone.service.MusicService;
@@ -18,6 +20,7 @@ import java.lang.ref.WeakReference;
  * @author Karim Abou Zeid (kabouzeid)
  */
 public abstract class AbsPlaybackControlActivity extends AbsBaseActivity {
+    @Nullable
     private MusicPlayerRemote.ServiceToken serviceToken;
     private PlaybackStatusReceiver playbackStatusReceiver;
 
@@ -88,6 +91,7 @@ public abstract class AbsPlaybackControlActivity extends AbsBaseActivity {
 
     private static final class PlaybackStatusReceiver extends BroadcastReceiver {
 
+        @NonNull
         private final WeakReference<AbsPlaybackControlActivity> reference;
 
         public PlaybackStatusReceiver(final AbsPlaybackControlActivity activity) {
@@ -95,7 +99,7 @@ public abstract class AbsPlaybackControlActivity extends AbsBaseActivity {
         }
 
         @Override
-        public void onReceive(final Context context, final Intent intent) {
+        public void onReceive(final Context context, @NonNull final Intent intent) {
             final String action = intent.getAction();
             switch (action) {
                 case MusicService.META_CHANGED:

app/src/main/java/com/kabouzeid/gramophone/ui/activities/base/AbsThemeActivity.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.ui.activities.base;
 import android.app.ActivityManager;
 import android.os.Build;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 import android.view.View;
 
@@ -21,6 +22,7 @@ public abstract class AbsThemeActivity extends AppCompatActivity implements KabV
     private int colorPrimaryDarker;
     private int colorAccent;
 
+    @Nullable
     private ActivityManager.TaskDescription taskDescription;
 
     @Override

app/src/main/java/com/kabouzeid/gramophone/ui/activities/tageditor/AbsTagEditorActivity.java

@@ -9,6 +9,8 @@ import android.media.MediaScannerConnection;
 import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.FloatingActionButton;
 import android.support.v7.graphics.Palette;
 import android.support.v7.widget.Toolbar;
@@ -52,7 +54,6 @@ import java.util.Map;
 
 import butterknife.ButterKnife;
 import butterknife.InjectView;
-import butterknife.Optional;
 
 /**
  * @author Karim Abou Zeid (kabouzeid)
@@ -77,7 +78,6 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
     ObservableScrollView observableScrollView;
     @InjectView(R.id.toolbar)
     Toolbar toolbar;
-    @Optional
     @InjectView(R.id.image)
     ImageView image;
     @InjectView(R.id.header)
@@ -220,9 +220,10 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
 
     protected abstract int getContentViewLayout();
 
+    @NonNull
     protected abstract List<String> getSongPaths();
 
-    protected void searchWebFor(List<String> strings) {
+    protected void searchWebFor(@NonNull List<String> strings) {
         StringBuilder stringBuilder = new StringBuilder();
         for (String string : strings) {
             stringBuilder.append(string);
@@ -234,7 +235,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
     }
 
     @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
         int id = item.getItemId();
         switch (id) {
             case android.R.id.home:
@@ -281,7 +282,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         setImageBitmap(bitmap);
     }
 
-    protected void setImageBitmap(final Bitmap bitmap) {
+    protected void setImageBitmap(@Nullable final Bitmap bitmap) {
         if (bitmap != null) {
             image.setImageBitmap(bitmap);
             applyPalette(bitmap);
@@ -290,12 +291,12 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         }
     }
 
-    private void applyPalette(final Bitmap bitmap) {
+    private void applyPalette(@NonNull final Bitmap bitmap) {
         Palette.from(bitmap)
                 .resizeBitmapSize(100)
                 .generate(new Palette.PaletteAsyncListener() {
                     @Override
-                    public void onGenerated(Palette palette) {
+                    public void onGenerated(@NonNull Palette palette) {
                         final Palette.Swatch vibrantSwatch = palette.getVibrantSwatch();
                         if (vibrantSwatch != null) {
                             paletteColorPrimary = palette.getVibrantColor(DialogUtils.resolveColor(AbsTagEditorActivity.this, R.attr.default_bar_color));
@@ -317,11 +318,11 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return true;
     }
 
-    protected void writeValuesToFiles(final Map<FieldKey, String> fieldKeyValueMap) {
+    protected void writeValuesToFiles(@NonNull final Map<FieldKey, String> fieldKeyValueMap) {
         writeValuesToFiles(fieldKeyValueMap, null, false);
     }
 
-    protected void writeValuesToFiles(final Map<FieldKey, String> fieldKeyValueMap, final Artwork artwork, final boolean deleteArtwork) {
+    protected void writeValuesToFiles(@NonNull final Map<FieldKey, String> fieldKeyValueMap, @Nullable final Artwork artwork, final boolean deleteArtwork) {
         Util.hideSoftKeyboard(this);
         final String writingFileStr = getResources().getString(R.string.writing_file_number);
         final MaterialDialog progressDialog = new MaterialDialog.Builder(AbsTagEditorActivity.this)
@@ -361,7 +362,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
                             tag.setField(artwork);
                         }
                         audioFile.commit();
-                    } catch (CannotReadException | IOException | TagException | ReadOnlyFileException | InvalidAudioFrameException e) {
+                    } catch (@NonNull CannotReadException | IOException | TagException | ReadOnlyFileException | InvalidAudioFrameException e) {
                         Log.e(TAG, "Error while reading audio file.", e);
                     } catch (CannotWriteException e) {
                         Log.e(TAG, "Error while writing audio file.", e);
@@ -390,7 +391,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         }).start();
     }
 
-    private void rescanMediaAndQuitOnFinish(final OnScannedAllListener listener) {
+    private void rescanMediaAndQuitOnFinish(@NonNull final OnScannedAllListener listener) {
         String[] toBeScanned = new String[songPaths.size()];
         toBeScanned = songPaths.toArray(toBeScanned);
         final int toBeScannedLength = toBeScanned.length;
@@ -418,7 +419,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return id;
     }
 
-    protected void writeValuesToFiles(final Map<FieldKey, String> fieldKeyValueMap, final Artwork artwork) {
+    protected void writeValuesToFiles(@NonNull final Map<FieldKey, String> fieldKeyValueMap, @Nullable final Artwork artwork) {
         if (artwork == null) {
             writeValuesToFiles(fieldKeyValueMap, null, true);
         } else {
@@ -426,12 +427,12 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         }
     }
 
-    protected void writeValuesToFiles(final Map<FieldKey, String> fieldKeyValueMap, boolean deleteArtwork) {
+    protected void writeValuesToFiles(@NonNull final Map<FieldKey, String> fieldKeyValueMap, boolean deleteArtwork) {
         writeValuesToFiles(fieldKeyValueMap, null, deleteArtwork);
     }
 
     @Override
-    protected void onActivityResult(int requestCode, int resultCode, Intent imageReturnedIntent) {
+    protected void onActivityResult(int requestCode, int resultCode, @NonNull Intent imageReturnedIntent) {
         super.onActivityResult(requestCode, resultCode, imageReturnedIntent);
         switch (requestCode) {
             case REQUEST_CODE_SELECT_IMAGE:
@@ -444,6 +445,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
 
     protected abstract void loadImageFromFile(Uri selectedFile);
 
+    @Nullable
     protected String getSongTitle() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.TITLE);
@@ -452,15 +454,16 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         }
     }
 
-    private AudioFile getAudioFile(String path) {
+    private AudioFile getAudioFile(@NonNull String path) {
         try {
             return AudioFileIO.read(new File(path));
-        } catch (CannotReadException | ReadOnlyFileException | InvalidAudioFrameException | TagException | IOException e) {
+        } catch (@NonNull CannotReadException | ReadOnlyFileException | InvalidAudioFrameException | TagException | IOException e) {
             Log.e(TAG, "Error while trying to create the AudioFile from java.io.File", e);
         }
         return null;
     }
 
+    @Nullable
     protected String getAlbumTitle() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.ALBUM);
@@ -469,6 +472,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return null;
     }
 
+    @Nullable
     protected String getArtistName() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.ARTIST);
@@ -477,6 +481,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return null;
     }
 
+    @Nullable
     protected String getAlbumArtistName() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.ALBUM_ARTIST);
@@ -485,6 +490,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return null;
     }
 
+    @Nullable
     protected String getGenreName() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.GENRE);
@@ -493,6 +499,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return null;
     }
 
+    @Nullable
     protected String getSongYear() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.YEAR);
@@ -501,6 +508,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return null;
     }
 
+    @Nullable
     protected String getTrackNumber() {
         try {
             return getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirst(FieldKey.TRACK);
@@ -509,6 +517,7 @@ public abstract class AbsTagEditorActivity extends AbsBaseActivity {
         return null;
     }
 
+    @Nullable
     protected Bitmap getAlbumArt() {
         try {
             Artwork artworkTag = getAudioFile(songPaths.get(0)).getTagOrCreateAndSetDefault().getFirstArtwork();

app/src/main/java/com/kabouzeid/gramophone/ui/activities/tageditor/AlbumTagEditorActivity.java

@@ -3,6 +3,7 @@ package com.kabouzeid.gramophone.ui.activities.tageditor;
 import android.graphics.Bitmap;
 import android.net.Uri;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 import android.text.Editable;
 import android.text.TextWatcher;
 import android.util.Log;
@@ -67,6 +68,7 @@ public class AlbumTagEditorActivity extends AbsTagEditorActivity implements Text
         setUpViews();
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -104,7 +106,7 @@ public class AlbumTagEditorActivity extends AbsTagEditorActivity implements Text
         }
         lastFMRestClient.getApiService().getAlbumInfo(albumTitleStr, albumArtistNameStr, new Callback<AlbumInfo>() {
             @Override
-            public void success(AlbumInfo albumInfo, Response response) {
+            public void success(@NonNull AlbumInfo albumInfo, Response response) {
                 if (albumInfo.getAlbum() != null) {
                     List<Image> images = albumInfo.getAlbum().getImage();
                     int lastIndexOfImages = images.size() - 1;
@@ -187,6 +189,7 @@ public class AlbumTagEditorActivity extends AbsTagEditorActivity implements Text
         return R.layout.activity_album_tag_editor;
     }
 
+    @NonNull
     @Override
     protected List<String> getSongPaths() {
         ArrayList<Song> songs = AlbumSongLoader.getAlbumSongList(this, getId());
@@ -198,7 +201,7 @@ public class AlbumTagEditorActivity extends AbsTagEditorActivity implements Text
     }
 
     @Override
-    protected void loadImageFromFile(final Uri selectedFileUri) {
+    protected void loadImageFromFile(@NonNull final Uri selectedFileUri) {
         ImageLoader.getInstance().loadImage(selectedFileUri.toString(),
                 new ImageSize(500, 500),
                 new SimpleImageLoadingListener() {

app/src/main/java/com/kabouzeid/gramophone/ui/activities/tageditor/SongTagEditorActivity.java

@@ -2,6 +2,7 @@ package com.kabouzeid.gramophone.ui.activities.tageditor;
 
 import android.net.Uri;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 import android.text.Editable;
 import android.text.TextWatcher;
 import android.widget.EditText;
@@ -45,6 +46,7 @@ public class SongTagEditorActivity extends AbsTagEditorActivity implements TextW
         setUpViews();
     }
 
+    @NonNull
     @Override
     public String getTag() {
         return TAG;
@@ -106,6 +108,7 @@ public class SongTagEditorActivity extends AbsTagEditorActivity implements TextW
         return R.layout.activity_song_tag_editor;
     }
 
+    @NonNull
     @Override
     protected List<String> getSongPaths() {
         ArrayList<String> paths = new ArrayList<>(1);

app/src/main/java/com/kabouzeid/gramophone/ui/fragments/mainactivityfragments/AbsMainActivityFragment.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.ui.fragments.mainactivityfragments;
 
 import android.os.Bundle;
+import android.support.annotation.NonNull;
 import android.support.v4.app.Fragment;
 
 import com.kabouzeid.gramophone.interfaces.KabViewsDisableAble;
@@ -12,6 +13,7 @@ import com.kabouzeid.gramophone.ui.activities.MainActivity;
 public abstract class AbsMainActivityFragment extends Fragment implements KabViewsDisableAble {
     private boolean areViewsEnabled;
 
+    @NonNull
     protected MainActivity getMainActivity() {
         return (MainActivity) getActivity();
     }

app/src/main/java/com/kabouzeid/gramophone/ui/fragments/mainactivityfragments/AbsMainActivityRecyclerViewFragment.java

@@ -2,6 +2,7 @@ package com.kabouzeid.gramophone.ui.fragments.mainactivityfragments;
 
 import android.os.Bundle;
 import android.support.annotation.LayoutRes;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.annotation.StringRes;
 import android.support.design.widget.AppBarLayout;
@@ -40,7 +41,7 @@ public abstract class AbsMainActivityRecyclerViewFragment extends AbsMainActivit
     private RecyclerView.Adapter mAdapter;
 
     @Override
-    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
+    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
         View view = inflater.inflate(getLayoutRes(), container, false);
         ButterKnife.inject(this, view);
         return view;
@@ -130,6 +131,7 @@ public abstract class AbsMainActivityRecyclerViewFragment extends AbsMainActivit
 
     protected abstract RecyclerView.LayoutManager createLayoutManager();
 
+    @NonNull
     protected abstract RecyclerView.Adapter createAdapter();
 
     @Override

app/src/main/java/com/kabouzeid/gramophone/ui/fragments/mainactivityfragments/AlbumViewFragment.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.ui.fragments.mainactivityfragments;
 
+import android.support.annotation.NonNull;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 
@@ -23,6 +24,7 @@ public class AlbumViewFragment extends AbsMainActivityRecyclerViewFragment {
         return layoutManager;
     }
 
+    @NonNull
     @Override
     protected RecyclerView.Adapter createAdapter() {
         return new AlbumAdapter(getMainActivity(), getMainActivity());

app/src/main/java/com/kabouzeid/gramophone/ui/fragments/mainactivityfragments/ArtistViewFragment.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.ui.fragments.mainactivityfragments;
 
+import android.support.annotation.NonNull;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 
@@ -13,11 +14,13 @@ public class ArtistViewFragment extends AbsMainActivityRecyclerViewFragment {
 
     public static final String TAG = ArtistViewFragment.class.getSimpleName();
 
+    @NonNull
     @Override
     protected RecyclerView.LayoutManager createLayoutManager() {
         return new GridLayoutManager(getActivity(), 1);
     }
 
+    @NonNull
     @Override
     protected RecyclerView.Adapter createAdapter() {
         return new ArtistAdapter(getMainActivity(), getMainActivity());

app/src/main/java/com/kabouzeid/gramophone/ui/fragments/mainactivityfragments/PlaylistViewFragment.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.ui.fragments.mainactivityfragments;
 
+import android.support.annotation.NonNull;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 
@@ -13,11 +14,13 @@ public class PlaylistViewFragment extends AbsMainActivityRecyclerViewFragment {
 
     public static final String TAG = PlaylistViewFragment.class.getSimpleName();
 
+    @NonNull
     @Override
     protected RecyclerView.LayoutManager createLayoutManager() {
         return new GridLayoutManager(getActivity(), 1);
     }
 
+    @NonNull
     @Override
     protected RecyclerView.Adapter createAdapter() {
         return new PlaylistAdapter(getMainActivity(), getMainActivity());

app/src/main/java/com/kabouzeid/gramophone/ui/fragments/mainactivityfragments/SongViewFragment.java

@@ -1,5 +1,6 @@
 package com.kabouzeid.gramophone.ui.fragments.mainactivityfragments;
 
+import android.support.annotation.NonNull;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 
@@ -13,11 +14,13 @@ public class SongViewFragment extends AbsMainActivityRecyclerViewFragment {
 
     public static final String TAG = SongViewFragment.class.getSimpleName();
 
+    @NonNull
     @Override
     protected RecyclerView.LayoutManager createLayoutManager() {
         return new GridLayoutManager(getActivity(), 1);
     }
 
+    @NonNull
     @Override
     protected RecyclerView.Adapter createAdapter() {
         return new SongAdapter(getMainActivity(), getMainActivity());

app/src/main/java/com/kabouzeid/gramophone/util/ImageUtil.java

@@ -4,6 +4,7 @@ import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.graphics.Point;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.view.Display;
 import android.view.WindowManager;
@@ -24,7 +25,7 @@ import java.io.IOException;
 public class ImageUtil {
 
     @Nullable
-    public static Bitmap getEmbeddedSongArt(File songFile, Context context) {
+    public static Bitmap getEmbeddedSongArt(File songFile, @NonNull Context context) {
         try {
             AudioFile audioFile = AudioFileIO.read(songFile);
             byte[] data = audioFile.getTag().getFirstArtwork().getBinaryData();
@@ -39,13 +40,13 @@ public class ImageUtil {
                 options.inJustDecodeBounds = false;
                 return BitmapFactory.decodeByteArray(data, 0, data.length, options);
             }
-        } catch (CannotReadException | TagException | IOException | ReadOnlyFileException | InvalidAudioFrameException e) {
+        } catch (@NonNull CannotReadException | TagException | IOException | ReadOnlyFileException | InvalidAudioFrameException e) {
             e.printStackTrace();
         }
         return null;
     }
 
-    public static int calculateInSampleSize(BitmapFactory.Options options, Context context) {
+    public static int calculateInSampleSize(@NonNull BitmapFactory.Options options, @NonNull Context context) {
 
         // Raw height and width of image
         final int height = options.outHeight;
@@ -76,7 +77,7 @@ public class ImageUtil {
         return inSampleSize;
     }
 
-    private static int getSmallerScreenSize(Context c) {
+    private static int getSmallerScreenSize(@NonNull Context c) {
         Display display = ((WindowManager) c.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
         Point size = new Point();
         display.getSize(size);

app/src/main/java/com/kabouzeid/gramophone/util/InternalStorageUtil.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.util;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -22,7 +23,7 @@ public final class InternalStorageUtil {
      * @param key     the filename
      * @param object  any {@link java.io.Serializable} object which will be written to the internal storage
      */
-    public static synchronized void writeObject(final Context context, final String key, final Object object) throws IOException {
+    public static synchronized void writeObject(@NonNull final Context context, @NonNull final String key, final Object object) throws IOException {
         // First write the object to a file with ".tmp" postfix,
         // so when an error occurs, we do not overwrite the original
         // file (if exists) with a corrupted file.
@@ -43,7 +44,7 @@ public final class InternalStorageUtil {
      * @param originalFileName the original filename
      * @param newFileName      the new filename
      */
-    public static synchronized void renameAppFile(final Context context, String originalFileName, String newFileName) {
+    public static synchronized void renameAppFile(@NonNull final Context context, String originalFileName, @NonNull String newFileName) {
         File originalFile = context.getFileStreamPath(originalFileName);
         File newFile = new File(originalFile.getParent(), newFileName);
         if (newFile.exists()) {
@@ -57,7 +58,7 @@ public final class InternalStorageUtil {
      * @param context a valid {@link Context}
      * @param key     the filename
      */
-    public static synchronized Object readObject(final Context context, String key) throws IOException,
+    public static synchronized Object readObject(@NonNull final Context context, String key) throws IOException,
             ClassNotFoundException {
         FileInputStream fis = context.openFileInput(key);
         ObjectInputStream ois = new ObjectInputStream(fis);

app/src/main/java/com/kabouzeid/gramophone/util/MusicUtil.java

@@ -12,6 +12,7 @@ import android.provider.BaseColumns;
 import android.provider.MediaStore;
 import android.provider.Settings;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.util.Log;
 import android.widget.Toast;
 
@@ -37,11 +38,13 @@ import java.util.List;
 public class MusicUtil {
     public static final String TAG = MusicUtil.class.getSimpleName();
 
-    public static String getAlbumImageLoaderString(Album album) {
+    @NonNull
+    public static String getAlbumImageLoaderString(@NonNull Album album) {
         return PhonographImageDownloader.SCHEME_ALBUM + album.id;
     }
 
-    public static String getSongImageLoaderString(Song song) {
+    @NonNull
+    public static String getSongImageLoaderString(@NonNull Song song) {
         return PhonographImageDownloader.SCHEME_SONG + song.albumId + "#" + song.data;
     }
 
@@ -57,14 +60,14 @@ public class MusicUtil {
     }
 
     @NonNull
-    public static Intent createShareSongFileIntent(final Song song) {
+    public static Intent createShareSongFileIntent(@NonNull final Song song) {
         return new Intent()
                 .setAction(Intent.ACTION_SEND)
                 .putExtra(Intent.EXTRA_STREAM, Uri.parse("file://" + song.data))
                 .setType("audio/*");
     }
 
-    public static void setRingtone(final Context context, final int id) {
+    public static void setRingtone(@NonNull final Context context, final int id) {
         final ContentResolver resolver = context.getContentResolver();
         final Uri uri = getSongUri(id);
         try {
@@ -72,7 +75,7 @@ public class MusicUtil {
             values.put(MediaStore.Audio.AudioColumns.IS_RINGTONE, "1");
             values.put(MediaStore.Audio.AudioColumns.IS_ALARM, "1");
             resolver.update(uri, values, null, null);
-        } catch (final UnsupportedOperationException ignored) {
+        } catch (@NonNull final UnsupportedOperationException ignored) {
             return;
         }
 
@@ -95,7 +98,8 @@ public class MusicUtil {
         }
     }
 
-    public static String getArtistInfoString(Context context, Artist artist) {
+    @NonNull
+    public static String getArtistInfoString(@NonNull Context context, @NonNull Artist artist) {
         return artist.songCount + " " + context.getResources().getString(R.string.songs) + " | " + artist.albumCount + " " + context.getResources().getString(R.string.albums);
     }
 
@@ -111,7 +115,7 @@ public class MusicUtil {
         return trackNumberToFix % 1000;
     }
 
-    public static void insertAlbumArt(Context context, int albumId, String path) {
+    public static void insertAlbumArt(@NonNull Context context, int albumId, String path) {
         ContentResolver contentResolver = context.getContentResolver();
 
         Uri artworkUri = Uri.parse("content://media/external/audio/albumart");
@@ -124,16 +128,18 @@ public class MusicUtil {
         contentResolver.insert(artworkUri, values);
     }
 
-    public static void deleteAlbumArt(Context context, int albumId) {
+    public static void deleteAlbumArt(@NonNull Context context, int albumId) {
         ContentResolver contentResolver = context.getContentResolver();
         Uri localUri = Uri.parse("content://media/external/audio/albumart");
         contentResolver.delete(ContentUris.withAppendedId(localUri, albumId), null, null);
     }
 
+    @NonNull
     public static File createAlbumArtFile(String name) {
         return new File(createAlbumArtDir(), name + System.currentTimeMillis());
     }
 
+    @NonNull
     @SuppressWarnings("ResultOfMethodCallIgnored")
     public static File createAlbumArtDir() {
         File albumArtDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), "/.albumart/");
@@ -148,7 +154,7 @@ public class MusicUtil {
         return albumArtDir;
     }
 
-    public static void deleteTracks(final Context context, final List<Song> songs) {
+    public static void deleteTracks(@NonNull final Context context, @NonNull final List<Song> songs) {
         final String[] projection = new String[]{
                 BaseColumns._ID, MediaStore.MediaColumns.DATA
         };
@@ -191,7 +197,7 @@ public class MusicUtil {
                         Log.e("MusicUtils", "Failed to delete file " + name);
                     }
                     cursor.moveToNext();
-                } catch (final SecurityException ex) {
+                } catch (@NonNull final SecurityException ex) {
                     cursor.moveToNext();
                 } catch (NullPointerException e) {
                     Log.e("MusicUtils", "Failed to find file " + name);
@@ -204,19 +210,19 @@ public class MusicUtil {
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.DATABASE_CHANGED));
     }
 
-    private static Playlist getFavoritesPlaylist(final Context context) {
+    private static Playlist getFavoritesPlaylist(@NonNull final Context context) {
         return PlaylistLoader.getPlaylist(context, context.getString(R.string.favorites));
     }
 
-    private static Playlist getOrCreateFavoritesPlaylist(final Context context) {
+    private static Playlist getOrCreateFavoritesPlaylist(@NonNull final Context context) {
         return PlaylistLoader.getPlaylist(context, PlaylistsUtil.createPlaylist(context, context.getString(R.string.favorites)));
     }
 
-    public static boolean isFavorite(final Context context, final Song song) {
+    public static boolean isFavorite(@NonNull final Context context, @NonNull final Song song) {
         return PlaylistsUtil.doPlaylistContains(context, getFavoritesPlaylist(context).id, song.id);
     }
 
-    public static void toggleFavorite(final Context context, final Song song) {
+    public static void toggleFavorite(@NonNull final Context context, @NonNull final Song song) {
         if (isFavorite(context, song)) {
             PlaylistsUtil.removeFromPlaylist(context, song, getFavoritesPlaylist(context).id);
         } else {
@@ -224,7 +230,7 @@ public class MusicUtil {
         }
     }
 
-    public static boolean isArtistNameUnknown(final String artistName) {
+    public static boolean isArtistNameUnknown(@Nullable final String artistName) {
         return artistName != null && (artistName.trim().toLowerCase().equals("unknown") || artistName.trim().toLowerCase().equals("<unknown>"));
     }
 }

app/src/main/java/com/kabouzeid/gramophone/util/NavigationUtil.java

@@ -4,6 +4,8 @@ import android.app.Activity;
 import android.content.ActivityNotFoundException;
 import android.content.Intent;
 import android.media.audiofx.AudioEffect;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.app.ActivityCompat;
 import android.support.v4.app.ActivityOptionsCompat;
 import android.support.v4.util.Pair;
@@ -25,7 +27,7 @@ import com.kabouzeid.gramophone.ui.activities.PlaylistDetailActivity;
  */
 public class NavigationUtil {
 
-    public static void goToArtist(final Activity activity, final int artistId, final Pair[] sharedViews) {
+    public static void goToArtist(final Activity activity, final int artistId, @Nullable final Pair[] sharedViews) {
         if (activity instanceof ArtistDetailActivity)
             return;
         if ((activity instanceof KabViewsDisableAble && ((KabViewsDisableAble) activity).areViewsEnabled()) || !(activity instanceof KabViewsDisableAble)) {
@@ -44,7 +46,7 @@ public class NavigationUtil {
         }
     }
 
-    public static void goToAlbum(final Activity activity, final int albumId, final Pair[] sharedViews) {
+    public static void goToAlbum(final Activity activity, final int albumId, @Nullable final Pair[] sharedViews) {
         if (activity instanceof AlbumDetailActivity)
             return;
         if ((activity instanceof KabViewsDisableAble && ((KabViewsDisableAble) activity).areViewsEnabled()) || !(activity instanceof KabViewsDisableAble)) {
@@ -63,7 +65,7 @@ public class NavigationUtil {
         }
     }
 
-    public static void goToPlaylist(final Activity activity, final Playlist playlist, final Pair[] sharedViews) {
+    public static void goToPlaylist(final Activity activity, final Playlist playlist, @Nullable final Pair[] sharedViews) {
         if ((activity instanceof KabViewsDisableAble && ((KabViewsDisableAble) activity).areViewsEnabled()) || !(activity instanceof KabViewsDisableAble)) {
             if (activity instanceof KabViewsDisableAble)
                 ((KabViewsDisableAble) activity).disableViews();
@@ -83,7 +85,7 @@ public class NavigationUtil {
         }
     }
 
-    public static void openCurrentPlayingIfPossible(final Activity activity, final Pair[] sharedViews) {
+    public static void openCurrentPlayingIfPossible(final Activity activity, @Nullable final Pair[] sharedViews) {
         if (activity instanceof MusicControllerActivity) {
             activity.onBackPressed();
             return;
@@ -107,7 +109,7 @@ public class NavigationUtil {
         }
     }
 
-    public static void openPlayingQueueDialog(final AppCompatActivity activity) {
+    public static void openPlayingQueueDialog(@NonNull final AppCompatActivity activity) {
         PlayingQueueDialog dialog = PlayingQueueDialog.create();
         if (dialog != null) {
             dialog.show(activity.getSupportFragmentManager(), "PLAY_QUEUE");
@@ -116,7 +118,7 @@ public class NavigationUtil {
         }
     }
 
-    public static void openEqualizer(final Activity activity) {
+    public static void openEqualizer(@NonNull final Activity activity) {
         final int sessionId = MusicPlayerRemote.getAudioSessionId();
         if (sessionId == AudioEffect.ERROR_BAD_VALUE) {
             Toast.makeText(activity, activity.getResources().getString(R.string.no_audio_ID), Toast.LENGTH_LONG).show();
@@ -126,7 +128,7 @@ public class NavigationUtil {
                 effects.putExtra(AudioEffect.EXTRA_AUDIO_SESSION, sessionId);
                 effects.putExtra(AudioEffect.EXTRA_CONTENT_TYPE, AudioEffect.CONTENT_TYPE_MUSIC);
                 activity.startActivityForResult(effects, 0);
-            } catch (final ActivityNotFoundException notFound) {
+            } catch (@NonNull final ActivityNotFoundException notFound) {
                 Toast.makeText(activity, activity.getResources().getString(R.string.no_equalizer), Toast.LENGTH_SHORT).show();
             }
         }

app/src/main/java/com/kabouzeid/gramophone/util/PlaylistsUtil.java

@@ -7,6 +7,8 @@ import android.database.Cursor;
 import android.net.Uri;
 import android.provider.BaseColumns;
 import android.provider.MediaStore;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.widget.Toast;
 
 import com.kabouzeid.gramophone.App;
@@ -24,7 +26,7 @@ import java.util.List;
  */
 public class PlaylistsUtil {
 
-    public static int createPlaylist(final Context context, final String name) {
+    public static int createPlaylist(@NonNull final Context context, @Nullable final String name) {
         int id = -1;
         if (name != null && name.length() > 0) {
             Cursor cursor = context.getContentResolver().query(MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI,
@@ -70,7 +72,7 @@ public class PlaylistsUtil {
 //        App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
 //    }
 
-    public static void deletePlaylists(final Context context, final ArrayList<Playlist> playlists) {
+    public static void deletePlaylists(@NonNull final Context context, @NonNull final ArrayList<Playlist> playlists) {
         final Uri uri = MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI;
         final StringBuilder selection = new StringBuilder();
         selection.append(MediaStore.Audio.Playlists._ID + " IN (");
@@ -85,13 +87,13 @@ public class PlaylistsUtil {
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }
 
-    public static void addToPlaylist(final Context context, final Song song, final int playlistId, final boolean showToastOnFinish) {
+    public static void addToPlaylist(@NonNull final Context context, final Song song, final int playlistId, final boolean showToastOnFinish) {
         List<Song> helperList = new ArrayList<>();
         helperList.add(song);
         addToPlaylist(context, helperList, playlistId, showToastOnFinish);
     }
 
-    public static void addToPlaylist(final Context context, final List<Song> songs, final int playlistId, final boolean showToastOnFinish) {
+    public static void addToPlaylist(@NonNull final Context context, @NonNull final List<Song> songs, final int playlistId, final boolean showToastOnFinish) {
         final int size = songs.size();
         final ContentResolver resolver = context.getContentResolver();
         final String[] projection = new String[]{
@@ -124,7 +126,8 @@ public class PlaylistsUtil {
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }
 
-    public static ContentValues[] makeInsertItems(final List<Song> songs, final int offset, int len, final int base) {
+    @NonNull
+    public static ContentValues[] makeInsertItems(@NonNull final List<Song> songs, final int offset, int len, final int base) {
         if (offset + len > songs.size()) {
             len = songs.size() - offset;
         }
@@ -139,7 +142,7 @@ public class PlaylistsUtil {
         return contentValues;
     }
 
-    public static void removeFromPlaylist(final Context context, final Song song, int playlistId) {
+    public static void removeFromPlaylist(@NonNull final Context context, @NonNull final Song song, int playlistId) {
         Uri uri = MediaStore.Audio.Playlists.Members.getContentUri(
                 "external", playlistId);
         String selection = MediaStore.Audio.Playlists.Members.AUDIO_ID + " =?";
@@ -149,7 +152,7 @@ public class PlaylistsUtil {
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }
 
-    public static void removeFromPlaylist(final Context context, final List<PlaylistSong> songs) {
+    public static void removeFromPlaylist(@NonNull final Context context, @NonNull final List<PlaylistSong> songs) {
         final int playlistId = songs.get(0).playlistId;
         Uri uri = MediaStore.Audio.Playlists.Members.getContentUri(
                 "external", playlistId);
@@ -165,7 +168,7 @@ public class PlaylistsUtil {
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }
 
-    public static boolean doPlaylistContains(final Context context, final long playlistId, final int songId) {
+    public static boolean doPlaylistContains(@NonNull final Context context, final long playlistId, final int songId) {
         if (playlistId != -1) {
             Cursor c = context.getContentResolver().query(
                     MediaStore.Audio.Playlists.Members.getContentUri("external", playlistId),
@@ -195,12 +198,12 @@ public class PlaylistsUtil {
 //        return 0;
 //    }
 
-    public static boolean moveItem(final Context context, int playlistId, int from, int to) {
+    public static boolean moveItem(@NonNull final Context context, int playlistId, int from, int to) {
         return MediaStore.Audio.Playlists.Members.moveItem(context.getContentResolver(),
                 playlistId, from, to);
     }
 
-    public static void renamePlaylist(final Context context, final long id, final String newName) {
+    public static void renamePlaylist(@NonNull final Context context, final long id, final String newName) {
         ContentValues contentValues = new ContentValues();
         contentValues.put(MediaStore.Audio.PlaylistsColumns.NAME, newName);
         context.getContentResolver().update(MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI,
@@ -210,7 +213,7 @@ public class PlaylistsUtil {
         App.bus.post(new DataBaseChangedEvent(DataBaseChangedEvent.PLAYLISTS_CHANGED));
     }
 
-    public static String getNameForPlaylist(final Context context, final long id) {
+    public static String getNameForPlaylist(@NonNull final Context context, final long id) {
         Cursor cursor = context.getContentResolver().query(
                 MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI,
                 new String[]{MediaStore.Audio.PlaylistsColumns.NAME},

app/src/main/java/com/kabouzeid/gramophone/util/PreferenceUtils.java

@@ -4,6 +4,8 @@ import android.annotation.SuppressLint;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.preference.PreferenceManager;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.kabouzeid.gramophone.R;
 
@@ -49,15 +51,16 @@ public final class PreferenceUtils {
 
     private static PreferenceUtils sInstance;
 
+    @NonNull
     private final Context mContext;
     private final SharedPreferences mPreferences;
 
-    public PreferenceUtils(final Context context) {
+    public PreferenceUtils(@NonNull final Context context) {
         mContext = context;
         mPreferences = PreferenceManager.getDefaultSharedPreferences(context);
     }
 
-    public static PreferenceUtils getInstance(final Context context) {
+    public static PreferenceUtils getInstance(@NonNull final Context context) {
         if (sInstance == null) {
             sInstance = new PreferenceUtils(context.getApplicationContext());
         }
@@ -204,29 +207,35 @@ public final class PreferenceUtils {
         return mPreferences.getBoolean(IGNORE_MEDIA_STORE_ARTWORK, false);
     }
 
+    @Nullable
     public final String getArtistSortOrder() {
         return mPreferences.getString(ARTIST_SORT_ORDER, SortOrder.ArtistSortOrder.ARTIST_A_Z);
     }
 
+    @Nullable
     public final String getArtistSongSortOrder() {
         return mPreferences.getString(ARTIST_SONG_SORT_ORDER,
                 SortOrder.ArtistSongSortOrder.SONG_A_Z);
     }
 
+    @Nullable
     public final String getArtistAlbumSortOrder() {
         return mPreferences.getString(ARTIST_ALBUM_SORT_ORDER,
                 SortOrder.ArtistAlbumSortOrder.ALBUM_YEAR_ASC);
     }
 
+    @Nullable
     public final String getAlbumSortOrder() {
         return mPreferences.getString(ALBUM_SORT_ORDER, SortOrder.AlbumSortOrder.ALBUM_A_Z);
     }
 
+    @Nullable
     public final String getAlbumSongSortOrder() {
         return mPreferences.getString(ALBUM_SONG_SORT_ORDER,
                 SortOrder.AlbumSongSortOrder.SONG_TRACK_LIST);
     }
 
+    @Nullable
     public final String getSongSortOrder() {
         return mPreferences.getString(SONG_SORT_ORDER, SortOrder.SongSortOrder.SONG_A_Z);
     }

app/src/main/java/com/kabouzeid/gramophone/util/Util.java

@@ -15,6 +15,8 @@ import android.os.Build;
 import android.support.annotation.AttrRes;
 import android.support.annotation.ColorInt;
 import android.support.annotation.DrawableRes;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.content.ContextCompat;
 import android.util.TypedValue;
 import android.view.View;
@@ -36,7 +38,7 @@ public class Util {
 //        return resId;
 //    }
 
-    public static int resolveColor(Context context, @AttrRes int colorAttr) {
+    public static int resolveColor(@NonNull Context context, @AttrRes int colorAttr) {
         TypedArray a = context.obtainStyledAttributes(new int[]{colorAttr});
         int resId = a.getColor(0, 0);
         a.recycle();
@@ -50,7 +52,7 @@ public class Util {
 //        return result;
 //    }
 
-    public static int getActionBarSize(Context context) {
+    public static int getActionBarSize(@NonNull Context context) {
         TypedValue typedValue = new TypedValue();
         int[] textSizeAttr = new int[]{R.attr.actionBarSize};
         int indexOfAttrTextSize = 0;
@@ -60,7 +62,7 @@ public class Util {
         return actionBarSize;
     }
 
-    public static int getStatusBarHeight(Context context) {
+    public static int getStatusBarHeight(@NonNull Context context) {
         int result = 0;
         int resourceId = context.getResources().getIdentifier("status_bar_height", "dimen", "android");
         if (resourceId > 0) {
@@ -69,7 +71,7 @@ public class Util {
         return result;
     }
 
-    public static int getNavigationBarHeight(Context context) {
+    public static int getNavigationBarHeight(@NonNull Context context) {
         int result = 0;
         int resourceId = context.getResources().getIdentifier("navigation_bar_height", "dimen", "android");
         if (resourceId > 0) {
@@ -96,7 +98,7 @@ public class Util {
 //    }
 
     @TargetApi(19)
-    public static void setStatusBarTranslucent(Window window, boolean translucent) {
+    public static void setStatusBarTranslucent(@NonNull Window window, boolean translucent) {
         if (translucent) {
             window.setFlags(
                     WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS,
@@ -112,12 +114,13 @@ public class Util {
                 WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
     }
 
-    public static void setAllowDrawUnderStatusBar(Window window) {
+    public static void setAllowDrawUnderStatusBar(@NonNull Window window) {
         window.getDecorView().setSystemUiVisibility(
                 View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                         | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
     }
 
+    @NonNull
     public static String getFileSizeString(long sizeInBytes) {
         long fileSizeInKB = sizeInBytes / 1024;
         long fileSizeInMB = fileSizeInKB / 1024;
@@ -142,7 +145,7 @@ public class Util {
 //        return Bitmap.createScaledBitmap(bitmap, albumArtSize, albumArtSize, false);
 //    }
 
-    public static void hideSoftKeyboard(Activity activity) {
+    public static void hideSoftKeyboard(@Nullable Activity activity) {
         if (activity != null) {
             View currentFocus = activity.getCurrentFocus();
             if (currentFocus != null) {
@@ -160,15 +163,15 @@ public class Util {
         return Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT;
     }
 
-    public static boolean isTablet(final Context context) {
+    public static boolean isTablet(@NonNull final Context context) {
         return context.getResources().getConfiguration().smallestScreenWidthDp >= 600;
     }
 
-    public static boolean isInPortraitMode(final Context context) {
+    public static boolean isInPortraitMode(@NonNull final Context context) {
         return context.getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT;
     }
 
-    public static Drawable getTintedDrawable(Context context, @DrawableRes int drawableResId, int color) {
+    public static Drawable getTintedDrawable(@NonNull Context context, @DrawableRes int drawableResId, int color) {
         Drawable drawable = ContextCompat.getDrawable(context, drawableResId);
         if (drawable != null) {
             drawable.setColorFilter(color, PorterDuff.Mode.SRC_IN);
@@ -195,6 +198,7 @@ public class Util {
         return (alpha << 24) + (0x00ffffff & Color.HSVToColor(hsv));
     }
 
+    @NonNull
     public static ColorStateList getEmptyColorStateList(int color) {
         return new ColorStateList(
                 new int[][]{
@@ -205,14 +209,14 @@ public class Util {
     }
 
     @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
-    public static boolean isRTL(Context context) {
+    public static boolean isRTL(@NonNull Context context) {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
             Configuration config = context.getResources().getConfiguration();
             return config.getLayoutDirection() == View.LAYOUT_DIRECTION_RTL;
         } else return false;
     }
 
-    public static Bitmap getResizedBitmap(Bitmap bm, int newHeight, int newWidth, boolean recycleOld) {
+    public static Bitmap getResizedBitmap(@NonNull Bitmap bm, int newHeight, int newWidth, boolean recycleOld) {
         int width = bm.getWidth();
         int height = bm.getHeight();
         float scaleWidth = ((float) newWidth) / width;

app/src/main/java/com/kabouzeid/gramophone/util/ViewUtil.java

@@ -3,6 +3,8 @@ package com.kabouzeid.gramophone.util;
 import android.animation.ArgbEvaluator;
 import android.animation.ObjectAnimator;
 import android.os.Build;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.internal.view.menu.ListMenuItemView;
 import android.support.v7.internal.view.menu.MenuPopupHelper;
 import android.view.View;
@@ -26,7 +28,7 @@ import java.lang.reflect.Field;
 public class ViewUtil {
     public final static int DEFAULT_COLOR_ANIMATION_DURATION = 500;
 
-    public static void disableViews(ViewGroup layout) {
+    public static void disableViews(@NonNull ViewGroup layout) {
         for (int i = 0; i < layout.getChildCount(); i++) {
             View child = layout.getChildAt(i);
             if (child instanceof ViewGroup) {
@@ -37,7 +39,7 @@ public class ViewUtil {
         }
     }
 
-    public static void enableViews(ViewGroup layout) {
+    public static void enableViews(@NonNull ViewGroup layout) {
         for (int i = 0; i < layout.getChildCount(); i++) {
             View child = layout.getChildAt(i);
             if (child instanceof ViewGroup) {
@@ -48,7 +50,7 @@ public class ViewUtil {
         }
     }
 
-    public static void setListViewHeightBasedOnChildren(ListView listView) {
+    public static void setListViewHeightBasedOnChildren(@NonNull ListView listView) {
         ListAdapter listAdapter = listView.getAdapter();
         if (listAdapter == null)
             return;
@@ -100,13 +102,13 @@ public class ViewUtil {
         animator.start();
     }
 
-    public static void setBackgroundAlpha(View view, float alpha, int baseColor) {
+    public static void setBackgroundAlpha(@NonNull View view, float alpha, int baseColor) {
         int a = Math.min(255, Math.max(0, (int) (alpha * 255))) << 24;
         int rgb = 0x00ffffff & baseColor;
         view.setBackgroundColor(a + rgb);
     }
 
-    public static void addOnGlobalLayoutListener(final View view, final Runnable runnable) {
+    public static void addOnGlobalLayoutListener(@NonNull final View view, @NonNull final Runnable runnable) {
         ViewTreeObserver vto = view.getViewTreeObserver();
         vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
             @Override
@@ -134,7 +136,7 @@ public class ViewUtil {
 //        }
 //    }
 
-    public static void setCheckBoxTintForMenu(MenuPopupHelper menuPopupHelper) {
+    public static void setCheckBoxTintForMenu(@Nullable MenuPopupHelper menuPopupHelper) {
         if (menuPopupHelper != null) {
             final ListView listView = menuPopupHelper.getPopup().getListView();
             listView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {

app/src/main/java/com/kabouzeid/gramophone/views/ColorView.java

@@ -9,6 +9,8 @@ import android.graphics.Matrix;
 import android.graphics.Paint;
 import android.graphics.PorterDuff;
 import android.graphics.PorterDuffColorFilter;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.util.AttributeSet;
 import android.widget.FrameLayout;
 
@@ -18,20 +20,23 @@ import com.kabouzeid.gramophone.util.Util;
 public class ColorView extends FrameLayout {
 
     private final Bitmap mCheck;
+    @NonNull
     private final Paint paint;
+    @NonNull
     private final Paint paintBorder;
+    @Nullable
     private Paint paintCheck;
     private final int borderWidth;
 
-    public ColorView(Context context) {
+    public ColorView(@NonNull Context context) {
         this(context, null, 0);
     }
 
-    public ColorView(Context context, AttributeSet attrs) {
+    public ColorView(@NonNull Context context, AttributeSet attrs) {
         this(context, attrs, 0);
     }
 
-    public ColorView(Context context, AttributeSet attrs, int defStyleAttr) {
+    public ColorView(@NonNull Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         final int checkSize = (int) context.getResources().getDimension(R.dimen.circle_view_check);
         mCheck = getResizedBitmap(BitmapFactory.decodeResource(context.getResources(),
@@ -47,7 +52,7 @@ public class ColorView extends FrameLayout {
         setWillNotDraw(false);
     }
 
-    private static Bitmap getResizedBitmap(Bitmap bm, int newHeight, int newWidth) {
+    private static Bitmap getResizedBitmap(@NonNull Bitmap bm, int newHeight, int newWidth) {
         int width = bm.getWidth();
         int height = bm.getHeight();
         float scaleWidth = ((float) newWidth) / width;
@@ -88,7 +93,7 @@ public class ColorView extends FrameLayout {
 
 
     @Override
-    protected void onDraw(Canvas canvas) {
+    protected void onDraw(@NonNull Canvas canvas) {
         super.onDraw(canvas);
 
         int canvasSize = canvas.getWidth();

app/src/main/java/com/kabouzeid/gramophone/views/DynamicSwitch.java

@@ -5,6 +5,7 @@ import android.content.res.ColorStateList;
 import android.graphics.Color;
 import android.graphics.PorterDuff;
 import android.graphics.drawable.Drawable;
+import android.support.annotation.NonNull;
 import android.support.v4.content.ContextCompat;
 import android.support.v4.graphics.ColorUtils;
 import android.support.v4.graphics.drawable.DrawableCompat;
@@ -25,17 +26,17 @@ public class DynamicSwitch extends SwitchCompat {
     static final int[] CHECKED_STATE_SET = new int[]{android.R.attr.state_checked};
     static final int[] EMPTY_STATE_SET = new int[0];
 
-    public DynamicSwitch(Context context) {
+    public DynamicSwitch(@NonNull Context context) {
         super(context);
         init();
     }
 
-    public DynamicSwitch(Context context, AttributeSet attrs) {
+    public DynamicSwitch(@NonNull Context context, AttributeSet attrs) {
         super(context, attrs);
         init();
     }
 
-    public DynamicSwitch(Context context, AttributeSet attrs, int defStyleAttr) {
+    public DynamicSwitch(@NonNull Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         init();
     }
@@ -45,7 +46,7 @@ public class DynamicSwitch extends SwitchCompat {
         setTint(this, color);
     }
 
-    public static void setTint(SwitchCompat switchCompat, int color) {
+    public static void setTint(@NonNull SwitchCompat switchCompat, int color) {
         ColorStateList trackColorSl = createSwitchTrackColorStateList(switchCompat.getContext(), color);
         ColorStateList thumbColorSl = createSwitchThumbColorStateList(switchCompat.getContext(), color);
 
@@ -59,7 +60,8 @@ public class DynamicSwitch extends SwitchCompat {
         switchCompat.setTrackDrawable(trackDrawable);
     }
 
-    private static ColorStateList createSwitchTrackColorStateList(Context context, int colorActivated) {
+    @NonNull
+    private static ColorStateList createSwitchTrackColorStateList(@NonNull Context context, int colorActivated) {
         final int[][] states = new int[3][];
         final int[] colors = new int[3];
         int i = 0;
@@ -80,7 +82,8 @@ public class DynamicSwitch extends SwitchCompat {
         return new ColorStateList(states, colors);
     }
 
-    private static ColorStateList createSwitchThumbColorStateList(Context context, int colorActivated) {
+    @NonNull
+    private static ColorStateList createSwitchThumbColorStateList(@NonNull Context context, int colorActivated) {
         final int[][] states = new int[3][];
         final int[] colors = new int[3];
         int i = 0;

app/src/main/java/com/kabouzeid/gramophone/views/FastScroller.java

@@ -8,6 +8,7 @@ import android.graphics.drawable.Drawable;
 import android.graphics.drawable.InsetDrawable;
 import android.graphics.drawable.StateListDrawable;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.widget.RecyclerView;
 import android.util.AttributeSet;
 import android.view.MotionEvent;
@@ -36,19 +37,20 @@ public class FastScroller extends FrameLayout {
     private boolean isHidden;
     private int hideTranslationX;
 
+    @Nullable
     private ViewPropertyAnimator currentAnimator = null;
 
-    public FastScroller(Context context, AttributeSet attrs) {
+    public FastScroller(@NonNull Context context, AttributeSet attrs) {
         super(context, attrs);
         initialise(context);
     }
 
-    public FastScroller(Context context, AttributeSet attrs, int defStyleAttr) {
+    public FastScroller(@NonNull Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         initialise(context);
     }
 
-    private void initialise(Context context) {
+    private void initialise(@NonNull Context context) {
         hideTranslationX = getContext().getResources().getDimensionPixelSize(R.dimen.scrollbar_width) * (Util.isRTL(context) ? -1 : 1);
         setClipChildren(false);
         inflate(context, R.layout.vertical_recycler_fast_scroller_layout, this);
@@ -76,7 +78,7 @@ public class FastScroller extends FrameLayout {
         return super.onTouchEvent(event);
     }
 
-    public void setRecyclerView(RecyclerView recyclerView) {
+    public void setRecyclerView(@NonNull RecyclerView recyclerView) {
         this.recyclerView = recyclerView;
         recyclerView.addOnScrollListener(scrollListener);
     }

app/src/main/java/com/kabouzeid/gramophone/views/HeightFitSquareImageView.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.views;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 import android.util.AttributeSet;
 import android.widget.ImageView;
 
@@ -13,11 +14,11 @@ public class HeightFitSquareImageView extends ImageView {
         super(context);
     }
 
-    public HeightFitSquareImageView(Context context, AttributeSet attrs) {
+    public HeightFitSquareImageView(@NonNull Context context, AttributeSet attrs) {
         super(context, attrs);
     }
 
-    public HeightFitSquareImageView(Context context, AttributeSet attrs, int defStyle) {
+    public HeightFitSquareImageView(@NonNull Context context, AttributeSet attrs, int defStyle) {
         super(context, attrs, defStyle);
     }
 

app/src/main/java/com/kabouzeid/gramophone/views/HeightWidthFitSquareImageView.java

@@ -1,6 +1,7 @@
 package com.kabouzeid.gramophone.views;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 import android.util.AttributeSet;
 import android.widget.ImageView;
 
@@ -13,11 +14,11 @@ public class HeightWidthFitSquareImageView extends ImageView {
         super(context);
     }
 
-    public HeightWidthFitSquareImageView(Context context, AttributeSet attrs) {
+    public HeightWidthFitSquareImageView(@NonNull Context context, AttributeSet attrs) {
         super(context, attrs);
     }
 
-    public HeightWidthFitSquareImageView(Context context, AttributeSet attrs, int defStyle) {
+    public HeightWidthFitSquareImageView(@NonNull Context context, AttributeSet attrs, int defStyle) {
         super(context, attrs, defStyle);
     }
 

app/src/main/java/com/kabouzeid/gramophone/views/PlayPauseDrawable.java

@@ -14,6 +14,7 @@ import android.graphics.Path;
 import android.graphics.PixelFormat;
 import android.graphics.Rect;
 import android.graphics.drawable.Drawable;
+import android.support.annotation.NonNull;
 import android.util.Property;
 import android.view.animation.DecelerateInterpolator;
 
@@ -25,12 +26,12 @@ public class PlayPauseDrawable extends Drawable {
     private static final Property<PlayPauseDrawable, Float> PROGRESS =
             new Property<PlayPauseDrawable, Float>(Float.class, "progress") {
                 @Override
-                public Float get(PlayPauseDrawable d) {
+                public Float get(@NonNull PlayPauseDrawable d) {
                     return d.getProgress();
                 }
 
                 @Override
-                public void set(PlayPauseDrawable d, Float value) {
+                public void set(@NonNull PlayPauseDrawable d, Float value) {
                     d.setProgress(value);
                 }
             };
@@ -51,7 +52,7 @@ public class PlayPauseDrawable extends Drawable {
 
     private AnimatorSet animatorSet;
 
-    public PlayPauseDrawable(Context context) {
+    public PlayPauseDrawable(@NonNull Context context) {
         final Resources res = context.getResources();
         paint.setAntiAlias(true);
         paint.setStyle(Paint.Style.FILL);
@@ -62,7 +63,7 @@ public class PlayPauseDrawable extends Drawable {
     }
 
     @Override
-    protected void onBoundsChange(final Rect bounds) {
+    protected void onBoundsChange(@NonNull final Rect bounds) {
         super.onBoundsChange(bounds);
         if (bounds.width() > 0 && bounds.height() > 0) {
             width = bounds.width();
@@ -71,7 +72,7 @@ public class PlayPauseDrawable extends Drawable {
     }
 
     @Override
-    public void draw(Canvas canvas) {
+    public void draw(@NonNull Canvas canvas) {
         leftPauseBar.rewind();
         rightPauseBar.rewind();
 
@@ -126,6 +127,7 @@ public class PlayPauseDrawable extends Drawable {
         canvas.restore();
     }
 
+    @NonNull
     private Animator getPausePlayAnimator() {
         isPlaySet = !isPlaySet;
         final Animator anim = ObjectAnimator.ofFloat(this, PROGRESS, isPlay ? 1 : 0, isPlay ? 0 : 1);