diff --git a/app/src/main/java/code/name/monkey/retromusic/adapter/CategoryInfoAdapter.java b/app/src/main/java/code/name/monkey/retromusic/adapter/CategoryInfoAdapter.java
index d9b7b693..2354bb9a 100644
--- a/app/src/main/java/code/name/monkey/retromusic/adapter/CategoryInfoAdapter.java
+++ b/app/src/main/java/code/name/monkey/retromusic/adapter/CategoryInfoAdapter.java
@@ -40,7 +40,7 @@ public class CategoryInfoAdapter extends RecyclerView.Adapter<CategoryInfoAdapte
     implements SwipeAndDragHelper.ActionCompletionContract {
 
   private List<CategoryInfo> categoryInfos;
-  private ItemTouchHelper touchHelper;
+  private final ItemTouchHelper touchHelper;
 
   public CategoryInfoAdapter() {
     SwipeAndDragHelper swipeAndDragHelper = new SwipeAndDragHelper(this);
@@ -128,15 +128,15 @@ public class CategoryInfoAdapter extends RecyclerView.Adapter<CategoryInfoAdapte
   }
 
   static class ViewHolder extends RecyclerView.ViewHolder {
-    private MaterialCheckBox checkBox;
-    private View dragView;
-    private TextView title;
+    private final MaterialCheckBox checkBox;
+    private final View dragView;
+    private final TextView title;
 
     ViewHolder(View view) {
       super(view);
       checkBox = view.findViewById(R.id.checkbox);
       checkBox.setButtonTintList(
-          ColorStateList.valueOf(ThemeStore.Companion.accentColor(checkBox.getContext())));
+              ColorStateList.valueOf(ThemeStore.Companion.accentColor(checkBox.getContext())));
       title = view.findViewById(R.id.title);
       dragView = view.findViewById(R.id.drag_view);
     }
diff --git a/app/src/main/java/code/name/monkey/retromusic/adapter/album/AlbumAdapter.kt b/app/src/main/java/code/name/monkey/retromusic/adapter/album/AlbumAdapter.kt
index 6ec336c4..63e9534a 100644
--- a/app/src/main/java/code/name/monkey/retromusic/adapter/album/AlbumAdapter.kt
+++ b/app/src/main/java/code/name/monkey/retromusic/adapter/album/AlbumAdapter.kt
@@ -130,7 +130,7 @@ open class AlbumAdapter(
     }
 
     override fun getName(album: Album): String {
-        return album.title!!
+        return album.title
     }
 
     override fun onMultipleItemAction(
diff --git a/app/src/main/java/code/name/monkey/retromusic/fragments/albums/AlbumDetailsViewModel.kt b/app/src/main/java/code/name/monkey/retromusic/fragments/albums/AlbumDetailsViewModel.kt
index 702217d2..4ac3fb66 100644
--- a/app/src/main/java/code/name/monkey/retromusic/fragments/albums/AlbumDetailsViewModel.kt
+++ b/app/src/main/java/code/name/monkey/retromusic/fragments/albums/AlbumDetailsViewModel.kt
@@ -54,7 +54,7 @@ class AlbumDetailsViewModel(
 
     fun getAlbumInfo(album: Album): LiveData<Result<LastFmAlbum>> = liveData {
         emit(Result.Loading)
-        emit(repository.albumInfo(album.artistName ?: "-", album.title ?: "-"))
+        emit(repository.albumInfo(album.artistName, album.title))
     }
 
     fun getMoreAlbums(artist: Artist): LiveData<List<Album>> = liveData(IO) {
diff --git a/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcEntry.java b/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcEntry.java
index 81682f8a..75fc63a4 100644
--- a/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcEntry.java
+++ b/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcEntry.java
@@ -19,13 +19,15 @@ import android.text.StaticLayout;
 import android.text.TextPaint;
 import android.text.TextUtils;
 
-/** 一行歌词实体 */
+/**
+ * 一行歌词实体
+ */
 class LrcEntry implements Comparable<LrcEntry> {
   public static final int GRAVITY_CENTER = 0;
   public static final int GRAVITY_LEFT = 1;
   public static final int GRAVITY_RIGHT = 2;
-  private long time;
-  private String text;
+  private final long time;
+  private final String text;
   private String secondText;
   private StaticLayout staticLayout;
   /** 歌词距离视图顶部的距离 */
diff --git a/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcView.java b/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcView.java
index a27f1a19..60f904bd 100644
--- a/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcView.java
+++ b/app/src/main/java/code/name/monkey/retromusic/lyrics/LrcView.java
@@ -43,15 +43,17 @@ import java.util.List;
 import code.name.monkey.retromusic.BuildConfig;
 import code.name.monkey.retromusic.R;
 
-/** 歌词 Created by wcy on 2015/11/9. */
+/**
+ * 歌词 Created by wcy on 2015/11/9.
+ */
 @SuppressLint("StaticFieldLeak")
 public class LrcView extends View {
   private static final long ADJUST_DURATION = 100;
   private static final long TIMELINE_KEEP_TIME = 4 * DateUtils.SECOND_IN_MILLIS;
 
-  private List<LrcEntry> mLrcEntryList = new ArrayList<>();
-  private TextPaint mLrcPaint = new TextPaint();
-  private TextPaint mTimePaint = new TextPaint();
+  private final List<LrcEntry> mLrcEntryList = new ArrayList<>();
+  private final TextPaint mLrcPaint = new TextPaint();
+  private final TextPaint mTimePaint = new TextPaint();
   private Paint.FontMetrics mTimeFontMetrics;
   private Drawable mPlayDrawable;
   private float mDividerHeight;
@@ -78,28 +80,30 @@ public class LrcView extends View {
   private boolean isTouching;
   private boolean isFling;
   private int mTextGravity; // 歌词显示位置，靠左/居中/靠右
-  private Runnable hideTimelineRunnable =
-      new Runnable() {
-        @Override
-        public void run() {
-          if (hasLrc() && isShowTimeline) {
-            isShowTimeline = false;
-            smoothScrollTo(mCurrentLine);
-          }
-        }
-      };
-  /** 手势监听器 */
-  private GestureDetector.SimpleOnGestureListener mSimpleOnGestureListener =
-      new GestureDetector.SimpleOnGestureListener() {
-        @Override
-        public boolean onDown(MotionEvent e) {
-          if (hasLrc() && mOnPlayClickListener != null) {
-            mScroller.forceFinished(true);
-            removeCallbacks(hideTimelineRunnable);
-            isTouching = true;
-            isShowTimeline = true;
-            invalidate();
-            return true;
+  private final Runnable hideTimelineRunnable =
+          new Runnable() {
+            @Override
+            public void run() {
+              if (hasLrc() && isShowTimeline) {
+                isShowTimeline = false;
+                smoothScrollTo(mCurrentLine);
+              }
+            }
+          };
+  /**
+   * 手势监听器
+   */
+  private final GestureDetector.SimpleOnGestureListener mSimpleOnGestureListener =
+          new GestureDetector.SimpleOnGestureListener() {
+            @Override
+            public boolean onDown(MotionEvent e) {
+              if (hasLrc() && mOnPlayClickListener != null) {
+                mScroller.forceFinished(true);
+                removeCallbacks(hideTimelineRunnable);
+                isTouching = true;
+                isShowTimeline = true;
+                invalidate();
+                return true;
           }
           return super.onDown(e);
         }
diff --git a/app/src/main/java/code/name/monkey/retromusic/misc/CustomFragmentStatePagerAdapter.java b/app/src/main/java/code/name/monkey/retromusic/misc/CustomFragmentStatePagerAdapter.java
index b8ff09bf..50ce6119 100644
--- a/app/src/main/java/code/name/monkey/retromusic/misc/CustomFragmentStatePagerAdapter.java
+++ b/app/src/main/java/code/name/monkey/retromusic/misc/CustomFragmentStatePagerAdapter.java
@@ -78,15 +78,17 @@ public abstract class CustomFragmentStatePagerAdapter extends PagerAdapter {
   private final FragmentManager mFragmentManager;
   private FragmentTransaction mCurTransaction = null;
 
-  private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
-  private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
+  private final ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
+  private final ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
   private Fragment mCurrentPrimaryItem = null;
 
   public CustomFragmentStatePagerAdapter(FragmentManager fm) {
     mFragmentManager = fm;
   }
 
-  /** Return the Fragment associated with a specified position. */
+  /**
+   * Return the Fragment associated with a specified position.
+   */
   public abstract Fragment getItem(int position);
 
   @Override
diff --git a/app/src/main/java/code/name/monkey/retromusic/misc/UpdateToastMediaScannerCompletionListener.java b/app/src/main/java/code/name/monkey/retromusic/misc/UpdateToastMediaScannerCompletionListener.java
index 1b6dd023..d749cf22 100644
--- a/app/src/main/java/code/name/monkey/retromusic/misc/UpdateToastMediaScannerCompletionListener.java
+++ b/app/src/main/java/code/name/monkey/retromusic/misc/UpdateToastMediaScannerCompletionListener.java
@@ -38,7 +38,7 @@ public class UpdateToastMediaScannerCompletionListener
     private final List<String> toBeScanned;
     private int failed = 0;
     private int scanned = 0;
-    private Toast toast;
+  private final Toast toast;
 
     @SuppressLint("ShowToast")
     public UpdateToastMediaScannerCompletionListener(Activity activity, List<String> toBeScanned) {
diff --git a/app/src/main/java/code/name/monkey/retromusic/model/Artist.kt b/app/src/main/java/code/name/monkey/retromusic/model/Artist.kt
index 12150c45..faf13398 100644
--- a/app/src/main/java/code/name/monkey/retromusic/model/Artist.kt
+++ b/app/src/main/java/code/name/monkey/retromusic/model/Artist.kt
@@ -30,9 +30,6 @@ data class Artist(
     }
 
     var name: String = ""
-        set(value) {
-            field = value
-        }
         get() {
             val name = if (isAlbumArtist) getAlbumArtistName()
             else getArtistName()
diff --git a/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmAlbum.java b/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmAlbum.java
index 481372ff..baef218f 100644
--- a/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmAlbum.java
+++ b/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmAlbum.java
@@ -112,7 +112,8 @@ public class LastFmAlbum {
 
     public class Tags {
 
-      @Expose private List<Tag> tag = null;
+      @Expose
+      private final List<Tag> tag = null;
 
       public List<Tag> getTag() {
         return tag;
diff --git a/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmTrack.java b/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmTrack.java
index cdaed55e..8319b15d 100644
--- a/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmTrack.java
+++ b/app/src/main/java/code/name/monkey/retromusic/network/model/LastFmTrack.java
@@ -84,7 +84,8 @@ public class LastFmTrack {
     }
 
     public static class Toptags {
-      @Expose private List<Tag> tag = null;
+      @Expose
+      private final List<Tag> tag = null;
 
       public List<Tag> getTag() {
         return tag;
diff --git a/app/src/main/java/code/name/monkey/retromusic/providers/BlacklistStore.java b/app/src/main/java/code/name/monkey/retromusic/providers/BlacklistStore.java
index bf274f66..90a89770 100644
--- a/app/src/main/java/code/name/monkey/retromusic/providers/BlacklistStore.java
+++ b/app/src/main/java/code/name/monkey/retromusic/providers/BlacklistStore.java
@@ -36,7 +36,7 @@ public class BlacklistStore extends SQLiteOpenHelper {
   public static final String DATABASE_NAME = "blacklist.db";
   private static final int VERSION = 2;
   private static BlacklistStore sInstance = null;
-  private Context context;
+  private final Context context;
 
   public BlacklistStore(final Context context) {
     super(context, DATABASE_NAME, null, VERSION);
diff --git a/app/src/main/java/code/name/monkey/retromusic/providers/SongPlayCountStore.java b/app/src/main/java/code/name/monkey/retromusic/providers/SongPlayCountStore.java
index fd74c907..771f06e1 100644
--- a/app/src/main/java/code/name/monkey/retromusic/providers/SongPlayCountStore.java
+++ b/app/src/main/java/code/name/monkey/retromusic/providers/SongPlayCountStore.java
@@ -34,24 +34,27 @@ public class SongPlayCountStore extends SQLiteOpenHelper {
   private static final int VERSION = 3;
   // how many weeks worth of playback to track
   private static final int NUM_WEEKS = 52;
-  @Nullable private static SongPlayCountStore sInstance = null;
+  @Nullable
+  private static SongPlayCountStore sInstance = null;
   // interpolator curve applied for measuring the curve
-  @NonNull private static Interpolator sInterpolator = new AccelerateInterpolator(1.5f);
+  @NonNull
+  private static final Interpolator sInterpolator = new AccelerateInterpolator(1.5f);
   // how high to multiply the interpolation curve
   @SuppressWarnings("FieldCanBeLocal")
-  private static int INTERPOLATOR_HEIGHT = 50;
+  private static final int INTERPOLATOR_HEIGHT = 50;
 
   // how high the base value is. The ratio of the Height to Base is what really matters
   @SuppressWarnings("FieldCanBeLocal")
-  private static int INTERPOLATOR_BASE = 25;
+  private static final int INTERPOLATOR_BASE = 25;
 
   @SuppressWarnings("FieldCanBeLocal")
-  private static int ONE_WEEK_IN_MS = 1000 * 60 * 60 * 24 * 7;
+  private static final int ONE_WEEK_IN_MS = 1000 * 60 * 60 * 24 * 7;
 
-  @NonNull private static String WHERE_ID_EQUALS = SongPlayCountColumns.ID + "=?";
+  @NonNull
+  private static final String WHERE_ID_EQUALS = SongPlayCountColumns.ID + "=?";
 
   // number of weeks since epoch time
-  private int mNumberOfWeeksSinceEpoch;
+  private final int mNumberOfWeeksSinceEpoch;
 
   // used to track if we've walked through the db and updated all the rows
   private boolean mDatabaseUpdated;
diff --git a/app/src/main/java/code/name/monkey/retromusic/repository/SortedCursor.java b/app/src/main/java/code/name/monkey/retromusic/repository/SortedCursor.java
index 0d1cbb30..531af65d 100644
--- a/app/src/main/java/code/name/monkey/retromusic/repository/SortedCursor.java
+++ b/app/src/main/java/code/name/monkey/retromusic/repository/SortedCursor.java
@@ -34,7 +34,7 @@ public class SortedCursor extends AbstractCursor {
   // the map of external indices to internal indices
   private ArrayList<Integer> mOrderedPositions;
   // this contains the ids that weren't found in the underlying cursor
-  private ArrayList<String> mMissingValues;
+  private final ArrayList<String> mMissingValues;
   // this contains the mapped cursor positions and afterwards the extra ids that weren't found
   private HashMap<String, Integer> mMapCursorPositions;
 
diff --git a/app/src/main/java/code/name/monkey/retromusic/repository/SortedLongCursor.java b/app/src/main/java/code/name/monkey/retromusic/repository/SortedLongCursor.java
index 9884a32e..75996d4a 100644
--- a/app/src/main/java/code/name/monkey/retromusic/repository/SortedLongCursor.java
+++ b/app/src/main/java/code/name/monkey/retromusic/repository/SortedLongCursor.java
@@ -34,7 +34,7 @@ public class SortedLongCursor extends AbstractCursor {
   // the map of external indices to internal indices
   private ArrayList<Integer> mOrderedPositions;
   // this contains the ids that weren't found in the underlying cursor
-  private ArrayList<Long> mMissingIds;
+  private final ArrayList<Long> mMissingIds;
   // this contains the mapped cursor positions and afterwards the extra ids that weren't found
   private HashMap<Long, Integer> mMapCursorPositions;
 
diff --git a/app/src/main/java/code/name/monkey/retromusic/service/MultiPlayer.java b/app/src/main/java/code/name/monkey/retromusic/service/MultiPlayer.java
index c0d7e023..4f59ab20 100644
--- a/app/src/main/java/code/name/monkey/retromusic/service/MultiPlayer.java
+++ b/app/src/main/java/code/name/monkey/retromusic/service/MultiPlayer.java
@@ -39,8 +39,9 @@ public class MultiPlayer
     private MediaPlayer mCurrentMediaPlayer = new MediaPlayer();
     private MediaPlayer mNextMediaPlayer;
 
-    private Context context;
-    @Nullable private Playback.PlaybackCallbacks callbacks;
+    private final Context context;
+  @Nullable
+  private Playback.PlaybackCallbacks callbacks;
 
     private boolean mIsInitialized = false;
 
diff --git a/app/src/main/java/code/name/monkey/retromusic/service/MusicService.java b/app/src/main/java/code/name/monkey/retromusic/service/MusicService.java
index 3ab626a0..04dc6d8b 100644
--- a/app/src/main/java/code/name/monkey/retromusic/service/MusicService.java
+++ b/app/src/main/java/code/name/monkey/retromusic/service/MusicService.java
@@ -187,15 +187,15 @@ public class MusicService extends MediaBrowserServiceCompat
 
     public int position = -1;
 
-    private AppWidgetBig appWidgetBig = AppWidgetBig.Companion.getInstance();
+    private final AppWidgetBig appWidgetBig = AppWidgetBig.Companion.getInstance();
 
-    private AppWidgetCard appWidgetCard = AppWidgetCard.Companion.getInstance();
+  private final AppWidgetCard appWidgetCard = AppWidgetCard.Companion.getInstance();
 
-    private AppWidgetClassic appWidgetClassic = AppWidgetClassic.Companion.getInstance();
+  private final AppWidgetClassic appWidgetClassic = AppWidgetClassic.Companion.getInstance();
 
-    private AppWidgetSmall appWidgetSmall = AppWidgetSmall.Companion.getInstance();
+  private final AppWidgetSmall appWidgetSmall = AppWidgetSmall.Companion.getInstance();
 
-    private AppWidgetText appWidgetText = AppWidgetText.Companion.getInstance();
+  private final AppWidgetText appWidgetText = AppWidgetText.Companion.getInstance();
 
     private final BroadcastReceiver widgetIntentReceiver =
             new BroadcastReceiver() {
@@ -229,15 +229,15 @@ public class MusicService extends MediaBrowserServiceCompat
                     }
                 }
             };
-    private AudioManager audioManager;
-    private IntentFilter becomingNoisyReceiverIntentFilter =
-            new IntentFilter(AudioManager.ACTION_AUDIO_BECOMING_NOISY);
-    private boolean becomingNoisyReceiverRegistered;
-    private IntentFilter bluetoothConnectedIntentFilter =
-            new IntentFilter(BluetoothDevice.ACTION_ACL_CONNECTED);
-    private boolean bluetoothConnectedRegistered = false;
-    private IntentFilter headsetReceiverIntentFilter = new IntentFilter(Intent.ACTION_HEADSET_PLUG);
-    private boolean headsetReceiverRegistered = false;
+  private AudioManager audioManager;
+  private final IntentFilter becomingNoisyReceiverIntentFilter =
+          new IntentFilter(AudioManager.ACTION_AUDIO_BECOMING_NOISY);
+  private boolean becomingNoisyReceiverRegistered;
+  private final IntentFilter bluetoothConnectedIntentFilter =
+          new IntentFilter(BluetoothDevice.ACTION_ACL_CONNECTED);
+  private boolean bluetoothConnectedRegistered = false;
+  private final IntentFilter headsetReceiverIntentFilter = new IntentFilter(Intent.ACTION_HEADSET_PLUG);
+  private boolean headsetReceiverRegistered = false;
     private MediaSessionCompat mediaSession;
     private ContentObserver mediaStoreObserver;
     private HandlerThread musicPlayerHandlerThread;
@@ -291,59 +291,59 @@ public class MusicService extends MediaBrowserServiceCompat
     private HandlerThread queueSaveHandlerThread;
     private boolean queuesRestored;
     private int repeatMode;
-    private int shuffleMode;
-    private SongPlayCountHelper songPlayCountHelper = new SongPlayCountHelper();
-    private final BroadcastReceiver bluetoothReceiver =
-            new BroadcastReceiver() {
-                @Override
-                public void onReceive(final Context context, final Intent intent) {
-                    String action = intent.getAction();
-                    if (action != null) {
-                        if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)
-                                && PreferenceUtil.INSTANCE.isBluetoothSpeaker()) {
-                            if (VERSION.SDK_INT >= VERSION_CODES.M) {
-                                if (getAudioManager().getDevices(AudioManager.GET_DEVICES_OUTPUTS).length > 0) {
+  private int shuffleMode;
+  private final SongPlayCountHelper songPlayCountHelper = new SongPlayCountHelper();
+  private final BroadcastReceiver bluetoothReceiver =
+          new BroadcastReceiver() {
+            @Override
+            public void onReceive(final Context context, final Intent intent) {
+              String action = intent.getAction();
+              if (action != null) {
+                if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)
+                        && PreferenceUtil.INSTANCE.isBluetoothSpeaker()) {
+                  if (VERSION.SDK_INT >= VERSION_CODES.M) {
+                    if (getAudioManager().getDevices(AudioManager.GET_DEVICES_OUTPUTS).length > 0) {
                                     play();
-                                }
-                            } else {
-                                if (getAudioManager().isBluetoothA2dpOn()) {
-                                    play();
-                                }
-                            }
-                        }
                     }
-                }
-            };
-    private PhoneStateListener phoneStateListener =
-            new PhoneStateListener() {
-                @Override
-                public void onCallStateChanged(int state, String incomingNumber) {
-                    switch (state) {
-                        case TelephonyManager.CALL_STATE_IDLE:
-                            // Not in call: Play music
-                            play();
-                            break;
-                        case TelephonyManager.CALL_STATE_RINGING:
-                        case TelephonyManager.CALL_STATE_OFFHOOK:
-                            // A call is dialing, active or on hold
-                            pause();
-                            break;
-                        default:
+                  } else {
+                    if (getAudioManager().isBluetoothA2dpOn()) {
+                      play();
                     }
-                    super.onCallStateChanged(state, incomingNumber);
+                  }
                 }
-            };
-    private BroadcastReceiver headsetReceiver =
-            new BroadcastReceiver() {
-                @Override
-                public void onReceive(Context context, Intent intent) {
-                    String action = intent.getAction();
-                    if (action != null) {
-                        if (Intent.ACTION_HEADSET_PLUG.equals(action)) {
-                            int state = intent.getIntExtra("state", -1);
-                            switch (state) {
-                                case 0:
-                                    pause();
+              }
+            }
+          };
+  private final PhoneStateListener phoneStateListener =
+          new PhoneStateListener() {
+            @Override
+            public void onCallStateChanged(int state, String incomingNumber) {
+              switch (state) {
+                case TelephonyManager.CALL_STATE_IDLE:
+                  // Not in call: Play music
+                  play();
+                  break;
+                case TelephonyManager.CALL_STATE_RINGING:
+                case TelephonyManager.CALL_STATE_OFFHOOK:
+                  // A call is dialing, active or on hold
+                  pause();
+                  break;
+                default:
+              }
+              super.onCallStateChanged(state, incomingNumber);
+            }
+          };
+  private final BroadcastReceiver headsetReceiver =
+          new BroadcastReceiver() {
+            @Override
+            public void onReceive(Context context, Intent intent) {
+              String action = intent.getAction();
+              if (action != null) {
+                if (Intent.ACTION_HEADSET_PLUG.equals(action)) {
+                  int state = intent.getIntExtra("state", -1);
+                  switch (state) {
+                    case 0:
+                      pause();
                                     break;
                                 case 1:
                                     play();
diff --git a/app/src/main/java/code/name/monkey/retromusic/util/AutoGeneratedPlaylistBitmap.java b/app/src/main/java/code/name/monkey/retromusic/util/AutoGeneratedPlaylistBitmap.java
index cf2e38f3..aea4fa1d 100644
--- a/app/src/main/java/code/name/monkey/retromusic/util/AutoGeneratedPlaylistBitmap.java
+++ b/app/src/main/java/code/name/monkey/retromusic/util/AutoGeneratedPlaylistBitmap.java
@@ -146,7 +146,7 @@ public class AutoGeneratedPlaylistBitmap {
         try {
             return Glide.with(context)
                     .asBitmap()
-                    .load(MusicUtil.INSTANCE.getMediaStoreAlbumCoverUri(id))
+                    .load(MusicUtil.getMediaStoreAlbumCoverUri(id))
                     .submit(200, 200)
                     .get();
         } catch (Exception e) {
diff --git a/app/src/main/java/code/name/monkey/retromusic/util/CalendarUtil.java b/app/src/main/java/code/name/monkey/retromusic/util/CalendarUtil.java
index b396df9a..28a75cc1 100644
--- a/app/src/main/java/code/name/monkey/retromusic/util/CalendarUtil.java
+++ b/app/src/main/java/code/name/monkey/retromusic/util/CalendarUtil.java
@@ -22,7 +22,7 @@ public class CalendarUtil {
   private static final long MS_PER_MINUTE = 60 * 1000;
   private static final long MS_PER_DAY = 24 * 60 * MS_PER_MINUTE;
 
-  private Calendar calendar;
+  private final Calendar calendar;
 
   public CalendarUtil() {
     this.calendar = Calendar.getInstance();
diff --git a/app/src/main/java/code/name/monkey/retromusic/util/PackageValidator.kt b/app/src/main/java/code/name/monkey/retromusic/util/PackageValidator.kt
index d75bd28b..352fb1e4 100644
--- a/app/src/main/java/code/name/monkey/retromusic/util/PackageValidator.kt
+++ b/app/src/main/java/code/name/monkey/retromusic/util/PackageValidator.kt
@@ -34,6 +34,8 @@ import org.xmlpull.v1.XmlPullParserException
 import java.io.IOException
 import java.security.MessageDigest
 import java.security.NoSuchAlgorithmException
+import java.util.*
+import kotlin.collections.LinkedHashMap
 
 /**
  * Validates that the calling package is authorized to browse a [MediaBrowserServiceCompat].
@@ -274,7 +276,8 @@ class PackageValidator(
         var eventType = parser.next()
         while (eventType != XmlResourceParser.END_TAG) {
             val isRelease = parser.getAttributeBooleanValue(null, "release", false)
-            val signature = parser.nextText().replace(WHITESPACE_REGEX, "").toLowerCase()
+            val signature = parser.nextText().replace(WHITESPACE_REGEX, "")
+                .lowercase(Locale.getDefault())
             callerSignatures += KnownSignature(signature, isRelease)
 
             eventType = parser.next()
@@ -319,14 +322,14 @@ class PackageValidator(
     }
 
     private data class KnownCallerInfo(
-            internal val name: String,
-            internal val packageName: String,
-            internal val signatures: MutableSet<KnownSignature>
+        val name: String,
+        val packageName: String,
+        val signatures: MutableSet<KnownSignature>
     )
 
     private data class KnownSignature(
-            internal val signature: String,
-            internal val release: Boolean
+        val signature: String,
+        val release: Boolean
     )
 
     /**
@@ -334,11 +337,11 @@ class PackageValidator(
      * to see if it's a known caller.
      */
     private data class CallerPackageInfo(
-            internal val name: String,
-            internal val packageName: String,
-            internal val uid: Int,
-            internal val signature: String?,
-            internal val permissions: Set<String>
+        val name: String,
+        val packageName: String,
+        val uid: Int,
+        val signature: String?,
+        val permissions: Set<String>
     )
 }
 
diff --git a/app/src/main/java/code/name/monkey/retromusic/util/SwipeAndDragHelper.java b/app/src/main/java/code/name/monkey/retromusic/util/SwipeAndDragHelper.java
index 2fdf3827..589f8d4b 100644
--- a/app/src/main/java/code/name/monkey/retromusic/util/SwipeAndDragHelper.java
+++ b/app/src/main/java/code/name/monkey/retromusic/util/SwipeAndDragHelper.java
@@ -22,7 +22,7 @@ import androidx.recyclerview.widget.RecyclerView;
 
 public class SwipeAndDragHelper extends ItemTouchHelper.Callback {
 
-  private ActionCompletionContract contract;
+  private final ActionCompletionContract contract;
 
   public SwipeAndDragHelper(@NonNull ActionCompletionContract contract) {
     this.contract = contract;
diff --git a/app/src/main/java/code/name/monkey/retromusic/util/color/MediaNotificationProcessor.java b/app/src/main/java/code/name/monkey/retromusic/util/color/MediaNotificationProcessor.java
index 6f17f982..80233a62 100644
--- a/app/src/main/java/code/name/monkey/retromusic/util/color/MediaNotificationProcessor.java
+++ b/app/src/main/java/code/name/monkey/retromusic/util/color/MediaNotificationProcessor.java
@@ -77,7 +77,7 @@ public class MediaNotificationProcessor {
 
   private static final String TAG = "ColorPicking";
   private float[] mFilteredBackgroundHsl = null;
-  private Palette.Filter mBlackWhiteFilter =
+  private final Palette.Filter mBlackWhiteFilter =
           (rgb, hsl) -> !isWhiteOrBlack(hsl);
   private boolean mIsLowPriority;
   private int backgroundColor;
@@ -85,7 +85,7 @@ public class MediaNotificationProcessor {
   private int primaryTextColor;
   private int actionBarColor;
   private Drawable drawable;
-  private Context context;
+  private final Context context;
 
   public MediaNotificationProcessor(Context context, Drawable drawable) {
     this.context = context;
diff --git a/app/src/main/java/code/name/monkey/retromusic/views/SeekArc.java b/app/src/main/java/code/name/monkey/retromusic/views/SeekArc.java
index 029ef96e..ccf533c4 100644
--- a/app/src/main/java/code/name/monkey/retromusic/views/SeekArc.java
+++ b/app/src/main/java/code/name/monkey/retromusic/views/SeekArc.java
@@ -38,14 +38,16 @@ import code.name.monkey.retromusic.R;
 public class SeekArc extends View {
 
   private static final String TAG = SeekArc.class.getSimpleName();
-  private static int INVALID_PROGRESS_VALUE = -1;
+  private static final int INVALID_PROGRESS_VALUE = -1;
   // The initial rotational offset -90 means we start at 12 o'clock
   private final int mAngleOffset = -90;
   private Paint mArcPaint;
   // Internal variables
   private int mArcRadius = 0;
-  private RectF mArcRect = new RectF();
-  /** The Width of the background arc for the SeekArc */
+  private final RectF mArcRect = new RectF();
+  /**
+   * The Width of the background arc for the SeekArc
+   */
   private int mArcWidth = 2;
   /** Will the progress increase clockwise or anti-clockwise */
   private boolean mClockwise = true;