diff --git a/app/src/main/java/com/google/android/material/appbar/FlingBehavior.java b/app/src/main/java/com/google/android/material/appbar/FlingBehavior.java
index ca1bd79d2..3e5f408f7 100644
--- a/app/src/main/java/com/google/android/material/appbar/FlingBehavior.java
+++ b/app/src/main/java/com/google/android/material/appbar/FlingBehavior.java
@@ -63,6 +63,7 @@ public final class FlingBehavior extends AppBarLayout.Behavior {
         return consumed == dy;
     }
 
+    @Override
     public boolean onInterceptTouchEvent(@NonNull final CoordinatorLayout parent,
                                          @NonNull final AppBarLayout child,
                                          @NonNull final MotionEvent ev) {
diff --git a/app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java b/app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java
index 6a956c6dc..a5e590ba0 100644
--- a/app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java
@@ -685,7 +685,7 @@ public final class VideoDetailFragment
         });
 
         setupBottomPlayer();
-        if (!playerHolder.bound) {
+        if (!playerHolder.isBound()) {
             setHeightThumbnail();
         } else {
             playerHolder.startService(false, this);
@@ -1434,7 +1434,7 @@ public final class VideoDetailFragment
                             bottomSheetBehavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
                         }
                         // Rebound to the service if it was closed via notification or mini player
-                        if (!playerHolder.bound) {
+                        if (!playerHolder.isBound()) {
                             playerHolder.startService(
                                     false, VideoDetailFragment.this);
                         }
diff --git a/app/src/main/java/org/schabi/newpipe/fragments/list/search/SearchFragment.java b/app/src/main/java/org/schabi/newpipe/fragments/list/search/SearchFragment.java
index 098df760d..15424334d 100644
--- a/app/src/main/java/org/schabi/newpipe/fragments/list/search/SearchFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/fragments/list/search/SearchFragment.java
@@ -724,7 +724,7 @@ public class SearchFragment extends BaseListFragment<SearchInfo, ListExtractor.I
     @Override
     public boolean onBackPressed() {
         if (suggestionsPanelVisible
-                && infoListAdapter.getItemsList().size() > 0
+                && !infoListAdapter.getItemsList().isEmpty()
                 && !isLoading.get()) {
             hideSuggestionsPanel();
             hideKeyboardSearch();
diff --git a/app/src/main/java/org/schabi/newpipe/local/subscription/item/ChannelItem.kt b/app/src/main/java/org/schabi/newpipe/local/subscription/item/ChannelItem.kt
index 2b964779c..a8c05838f 100644
--- a/app/src/main/java/org/schabi/newpipe/local/subscription/item/ChannelItem.kt
+++ b/app/src/main/java/org/schabi/newpipe/local/subscription/item/ChannelItem.kt
@@ -54,11 +54,9 @@ class ChannelItem(
             context.getString(R.string.subscribers_count_not_available)
         }
 
-        if (itemVersion == ItemVersion.NORMAL) {
-            if (infoItem.streamCount >= 0) {
-                val formattedVideoAmount = Localization.localizeStreamCount(context, infoItem.streamCount)
-                details = Localization.concatenateStrings(details, formattedVideoAmount)
-            }
+        if (itemVersion == ItemVersion.NORMAL && infoItem.streamCount >= 0) {
+            val formattedVideoAmount = Localization.localizeStreamCount(context, infoItem.streamCount)
+            details = Localization.concatenateStrings(details, formattedVideoAmount)
         }
         return details
     }
diff --git a/app/src/main/java/org/schabi/newpipe/player/Player.java b/app/src/main/java/org/schabi/newpipe/player/Player.java
index ee09cb866..c038f5573 100644
--- a/app/src/main/java/org/schabi/newpipe/player/Player.java
+++ b/app/src/main/java/org/schabi/newpipe/player/Player.java
@@ -2348,7 +2348,8 @@ public final class Player implements
         NotificationUtil.getInstance().createNotificationIfNeededAndUpdate(this, false);
     }
 
-    private void setRepeatModeButton(final AppCompatImageButton imageButton, final int repeatMode) {
+    private void setRepeatModeButton(final AppCompatImageButton imageButton,
+                                     @RepeatMode final int repeatMode) {
         switch (repeatMode) {
             case REPEAT_MODE_OFF:
                 imageButton.setImageResource(R.drawable.exo_controls_repeat_off);
@@ -2362,7 +2363,7 @@ public final class Player implements
         }
     }
 
-    private void setShuffleButton(final ImageButton button, final boolean shuffled) {
+    private void setShuffleButton(@NonNull final ImageButton button, final boolean shuffled) {
         button.setImageAlpha(shuffled ? 255 : 77);
     }
     //endregion
@@ -2387,7 +2388,7 @@ public final class Player implements
         return !exoPlayerIsNull() && simpleExoPlayer.getVolume() == 0;
     }
 
-    private void setMuteButton(final ImageButton button, final boolean isMuted) {
+    private void setMuteButton(@NonNull final ImageButton button, final boolean isMuted) {
         button.setImageDrawable(AppCompatResources.getDrawable(context, isMuted
                 ? R.drawable.ic_volume_off : R.drawable.ic_volume_up));
     }
@@ -2876,7 +2877,7 @@ public final class Player implements
         databaseUpdateDisposable
                 .add(recordManager.saveStreamState(currentMetadata.getMetadata(), progressMillis)
                 .observeOn(AndroidSchedulers.mainThread())
-                .doOnError((e) -> {
+                .doOnError(e -> {
                     if (DEBUG) {
                         e.printStackTrace();
                     }
@@ -3386,7 +3387,7 @@ public final class Player implements
         playbackSpeedPopupMenu.setOnDismissListener(this);
     }
 
-    private void buildCaptionMenu(final List<String> availableLanguages) {
+    private void buildCaptionMenu(@NonNull final List<String> availableLanguages) {
         if (captionPopupMenu == null) {
             return;
         }
@@ -3454,7 +3455,7 @@ public final class Player implements
      * Called when an item of the quality selector or the playback speed selector is selected.
      */
     @Override
-    public boolean onMenuItemClick(final MenuItem menuItem) {
+    public boolean onMenuItemClick(@NonNull final MenuItem menuItem) {
         if (DEBUG) {
             Log.d(TAG, "onMenuItemClick() called with: "
                     + "menuItem = [" + menuItem + "], "
@@ -3491,7 +3492,7 @@ public final class Player implements
      * Called when some popup menu is dismissed.
      */
     @Override
-    public void onDismiss(final PopupMenu menu) {
+    public void onDismiss(@Nullable final PopupMenu menu) {
         if (DEBUG) {
             Log.d(TAG, "onDismiss() called with: menu = [" + menu + "]");
         }
@@ -3544,7 +3545,7 @@ public final class Player implements
         isSomePopupMenuVisible = true;
     }
 
-    private void setPlaybackQuality(final String quality) {
+    private void setPlaybackQuality(@Nullable final String quality) {
         videoResolver.setPlaybackQuality(quality);
     }
     //endregion
@@ -3568,7 +3569,7 @@ public final class Player implements
             final int minimumLength = Math.min(metrics.heightPixels, metrics.widthPixels);
             final float captionRatioInverse = 20f + 4f * (1.0f - captionScale);
             binding.subtitleView.setFixedTextSize(
-                    TypedValue.COMPLEX_UNIT_PX, (float) minimumLength / captionRatioInverse);
+                    TypedValue.COMPLEX_UNIT_PX, minimumLength / captionRatioInverse);
         }
         binding.subtitleView.setApplyEmbeddedStyles(captionStyle == CaptionStyleCompat.DEFAULT);
         binding.subtitleView.setStyle(captionStyle);
@@ -3845,7 +3846,7 @@ public final class Player implements
     }
 
     @Override // exoplayer listener
-    public void onVideoSizeChanged(final VideoSize videoSize) {
+    public void onVideoSizeChanged(@NonNull final VideoSize videoSize) {
         if (DEBUG) {
             Log.d(TAG, "onVideoSizeChanged() called with: "
                     + "width / height = [" + videoSize.width + " / " + videoSize.height
@@ -3959,7 +3960,7 @@ public final class Player implements
         }
     }
 
-    private int distanceFromCloseButton(final MotionEvent popupMotionEvent) {
+    private int distanceFromCloseButton(@NonNull final MotionEvent popupMotionEvent) {
         final int closeOverlayButtonX = closeOverlayBinding.closeButton.getLeft()
                 + closeOverlayBinding.closeButton.getWidth() / 2;
         final int closeOverlayButtonY = closeOverlayBinding.closeButton.getTop()
@@ -3978,7 +3979,7 @@ public final class Player implements
         return buttonRadius * 1.2f;
     }
 
-    public boolean isInsideClosingRadius(final MotionEvent popupMotionEvent) {
+    public boolean isInsideClosingRadius(@NonNull final MotionEvent popupMotionEvent) {
         return distanceFromCloseButton(popupMotionEvent) <= getClosingRadius();
     }
     //endregion
@@ -4098,6 +4099,7 @@ public final class Player implements
         }
     }
 
+    @Nullable
     public AppCompatActivity getParentActivity() {
         // ! instanceof ViewGroup means that view was added via windowManager for Popup
         if (binding == null || !(binding.getRoot().getParent() instanceof ViewGroup)) {
diff --git a/app/src/main/java/org/schabi/newpipe/player/event/PlayerGestureListener.java b/app/src/main/java/org/schabi/newpipe/player/event/PlayerGestureListener.java
index e55c596b8..25ace1c05 100644
--- a/app/src/main/java/org/schabi/newpipe/player/event/PlayerGestureListener.java
+++ b/app/src/main/java/org/schabi/newpipe/player/event/PlayerGestureListener.java
@@ -1,5 +1,12 @@
 package org.schabi.newpipe.player.event;
 
+import static org.schabi.newpipe.ktx.AnimationType.ALPHA;
+import static org.schabi.newpipe.ktx.AnimationType.SCALE_AND_ALPHA;
+import static org.schabi.newpipe.ktx.ViewUtils.animate;
+import static org.schabi.newpipe.player.Player.DEFAULT_CONTROLS_DURATION;
+import static org.schabi.newpipe.player.Player.DEFAULT_CONTROLS_HIDE_TIME;
+import static org.schabi.newpipe.player.Player.STATE_PLAYING;
+
 import android.app.Activity;
 import android.util.Log;
 import android.view.MotionEvent;
@@ -8,22 +15,15 @@ import android.view.Window;
 import android.view.WindowManager;
 import android.widget.ProgressBar;
 
+import androidx.annotation.NonNull;
 import androidx.appcompat.content.res.AppCompatResources;
 
-import org.jetbrains.annotations.NotNull;
 import org.schabi.newpipe.MainActivity;
 import org.schabi.newpipe.R;
 import org.schabi.newpipe.player.MainPlayer;
 import org.schabi.newpipe.player.Player;
 import org.schabi.newpipe.player.helper.PlayerHelper;
 
-import static org.schabi.newpipe.ktx.AnimationType.ALPHA;
-import static org.schabi.newpipe.ktx.AnimationType.SCALE_AND_ALPHA;
-import static org.schabi.newpipe.ktx.ViewUtils.animate;
-import static org.schabi.newpipe.player.Player.DEFAULT_CONTROLS_DURATION;
-import static org.schabi.newpipe.player.Player.DEFAULT_CONTROLS_HIDE_TIME;
-import static org.schabi.newpipe.player.Player.STATE_PLAYING;
-
 /**
  * GestureListener for the player
  *
@@ -45,8 +45,8 @@ public class PlayerGestureListener
     }
 
     @Override
-    public void onDoubleTap(@NotNull final MotionEvent event,
-                            @NotNull final DisplayPortion portion) {
+    public void onDoubleTap(@NonNull final MotionEvent event,
+                            @NonNull final DisplayPortion portion) {
         if (DEBUG) {
             Log.d(TAG, "onDoubleTap called with playerType = ["
                     + player.getPlayerType() + "], portion = [" + portion + "]");
@@ -65,7 +65,7 @@ public class PlayerGestureListener
     }
 
     @Override
-    public void onSingleTap(@NotNull final MainPlayer.PlayerType playerType) {
+    public void onSingleTap(@NonNull final MainPlayer.PlayerType playerType) {
         if (DEBUG) {
             Log.d(TAG, "onSingleTap called with playerType = [" + player.getPlayerType() + "]");
         }
@@ -85,10 +85,10 @@ public class PlayerGestureListener
     }
 
     @Override
-    public void onScroll(@NotNull final MainPlayer.PlayerType playerType,
-                         @NotNull final DisplayPortion portion,
-                         @NotNull final MotionEvent initialEvent,
-                         @NotNull final MotionEvent movingEvent,
+    public void onScroll(@NonNull final MainPlayer.PlayerType playerType,
+                         @NonNull final DisplayPortion portion,
+                         @NonNull final MotionEvent initialEvent,
+                         @NonNull final MotionEvent movingEvent,
                          final float distanceX, final float distanceY) {
         if (DEBUG) {
             Log.d(TAG, "onScroll called with playerType = ["
@@ -197,8 +197,8 @@ public class PlayerGestureListener
     }
 
     @Override
-    public void onScrollEnd(@NotNull final MainPlayer.PlayerType playerType,
-                            @NotNull final MotionEvent event) {
+    public void onScrollEnd(@NonNull final MainPlayer.PlayerType playerType,
+                            @NonNull final MotionEvent event) {
         if (DEBUG) {
             Log.d(TAG, "onScrollEnd called with playerType = ["
                 + player.getPlayerType() + "]");
diff --git a/app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java b/app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java
index 46239cab1..10e315667 100644
--- a/app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java
+++ b/app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java
@@ -35,13 +35,13 @@ public final class PlayerHolder {
         return PlayerHolder.instance;
     }
 
-    private final boolean DEBUG = MainActivity.DEBUG;
-    private final String TAG = PlayerHolder.class.getSimpleName();
+    private static final boolean DEBUG = MainActivity.DEBUG;
+    private static final String TAG = PlayerHolder.class.getSimpleName();
 
     private PlayerServiceExtendedEventListener listener;
 
     private final PlayerServiceConnection serviceConnection = new PlayerServiceConnection();
-    public boolean bound;
+    private boolean bound;
     private MainPlayer playerService;
     private Player player;
 
@@ -70,6 +70,10 @@ public final class PlayerHolder {
         return player != null;
     }
 
+    public boolean isBound() {
+        return bound;
+    }
+
     public int getQueueSize() {
         return isPlayerOpen() ? player.getPlayQueue().size() : 0;
     }
@@ -148,7 +152,7 @@ public final class PlayerHolder {
             }
             startPlayerListener();
         }
-    };
+    }
 
     private void bind(final Context context) {
         if (DEBUG) {
diff --git a/app/src/main/java/org/schabi/newpipe/settings/BasePreferenceFragment.java b/app/src/main/java/org/schabi/newpipe/settings/BasePreferenceFragment.java
index 8b2bd9c9a..a745861ad 100644
--- a/app/src/main/java/org/schabi/newpipe/settings/BasePreferenceFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/settings/BasePreferenceFragment.java
@@ -18,7 +18,7 @@ import java.util.Objects;
 
 public abstract class BasePreferenceFragment extends PreferenceFragmentCompat {
     protected final String TAG = getClass().getSimpleName() + "@" + Integer.toHexString(hashCode());
-    protected final boolean DEBUG = MainActivity.DEBUG;
+    protected static final boolean DEBUG = MainActivity.DEBUG;
 
     SharedPreferences defaultPreferences;
 
diff --git a/app/src/main/java/org/schabi/newpipe/settings/tabs/Tab.java b/app/src/main/java/org/schabi/newpipe/settings/tabs/Tab.java
index eac5ce311..aa03bbfa6 100644
--- a/app/src/main/java/org/schabi/newpipe/settings/tabs/Tab.java
+++ b/app/src/main/java/org/schabi/newpipe/settings/tabs/Tab.java
@@ -36,6 +36,10 @@ import java.util.Objects;
 public abstract class Tab {
     private static final String JSON_TAB_ID_KEY = "tab_id";
 
+    private static final String NO_NAME = "<no-name>";
+    private static final String NO_ID = "<no-id>";
+    private static final String NO_URL = "<no-url>";
+
     Tab() {
     }
 
@@ -185,7 +189,9 @@ public abstract class Tab {
 
         @Override
         public String getTabName(final Context context) {
-            return "NewPipe"; //context.getString(R.string.blank_page_summary);
+            // TODO: find a better name for the blank tab (maybe "blank_tab") or replace it with
+            //       context.getString(R.string.app_name);
+            return "NewPipe"; // context.getString(R.string.blank_page_summary);
         }
 
         @DrawableRes
@@ -309,7 +315,7 @@ public abstract class Tab {
         private String kioskId;
 
         private KioskTab() {
-            this(-1, "<no-id>");
+            this(-1, NO_ID);
         }
 
         public KioskTab(final int kioskServiceId, final String kioskId) {
@@ -357,7 +363,7 @@ public abstract class Tab {
         @Override
         protected void readDataFromJson(final JsonObject jsonObject) {
             kioskServiceId = jsonObject.getInt(JSON_KIOSK_SERVICE_ID_KEY, -1);
-            kioskId = jsonObject.getString(JSON_KIOSK_ID_KEY, "<no-id>");
+            kioskId = jsonObject.getString(JSON_KIOSK_ID_KEY, NO_ID);
         }
 
         @Override
@@ -395,7 +401,7 @@ public abstract class Tab {
         private String channelName;
 
         private ChannelTab() {
-            this(-1, "<no-url>", "<no-name>");
+            this(-1, NO_URL, NO_NAME);
         }
 
         public ChannelTab(final int channelServiceId, final String channelUrl,
@@ -440,8 +446,8 @@ public abstract class Tab {
         @Override
         protected void readDataFromJson(final JsonObject jsonObject) {
             channelServiceId = jsonObject.getInt(JSON_CHANNEL_SERVICE_ID_KEY, -1);
-            channelUrl = jsonObject.getString(JSON_CHANNEL_URL_KEY, "<no-url>");
-            channelName = jsonObject.getString(JSON_CHANNEL_NAME_KEY, "<no-name>");
+            channelUrl = jsonObject.getString(JSON_CHANNEL_URL_KEY, NO_URL);
+            channelName = jsonObject.getString(JSON_CHANNEL_NAME_KEY, NO_NAME);
         }
 
         @Override
@@ -527,7 +533,7 @@ public abstract class Tab {
         private LocalItemType playlistType;
 
         private PlaylistTab() {
-            this(-1, "<no-name>");
+            this(-1, NO_NAME);
         }
 
         public PlaylistTab(final long playlistId, final String playlistName) {
@@ -535,7 +541,7 @@ public abstract class Tab {
             this.playlistId = playlistId;
             this.playlistType = LocalItemType.PLAYLIST_LOCAL_ITEM;
             this.playlistServiceId = -1;
-            this.playlistUrl = "<no-url>";
+            this.playlistUrl = NO_URL;
         }
 
         public PlaylistTab(final int playlistServiceId, final String playlistUrl,
@@ -589,8 +595,8 @@ public abstract class Tab {
         @Override
         protected void readDataFromJson(final JsonObject jsonObject) {
             playlistServiceId = jsonObject.getInt(JSON_PLAYLIST_SERVICE_ID_KEY, -1);
-            playlistUrl = jsonObject.getString(JSON_PLAYLIST_URL_KEY, "<no-url>");
-            playlistName = jsonObject.getString(JSON_PLAYLIST_NAME_KEY, "<no-name>");
+            playlistUrl = jsonObject.getString(JSON_PLAYLIST_URL_KEY, NO_URL);
+            playlistName = jsonObject.getString(JSON_PLAYLIST_NAME_KEY, NO_NAME);
             playlistId = jsonObject.getInt(JSON_PLAYLIST_ID_KEY, -1);
             playlistType = LocalItemType.valueOf(
                     jsonObject.getString(JSON_PLAYLIST_TYPE_KEY,
diff --git a/app/src/main/java/us/shandian/giga/io/FileStreamSAF.java b/app/src/main/java/us/shandian/giga/io/FileStreamSAF.java
index 000900918..b7dd0a103 100644
--- a/app/src/main/java/us/shandian/giga/io/FileStreamSAF.java
+++ b/app/src/main/java/us/shandian/giga/io/FileStreamSAF.java
@@ -108,10 +108,12 @@ public class FileStreamSAF extends SharpStream {
         return true;
     }
 
+    @Override
     public boolean canSetLength() {
         return true;
     }
 
+    @Override
     public boolean canSeek() {
         return true;
     }
@@ -131,10 +133,12 @@ public class FileStreamSAF extends SharpStream {
         out.write(buffer, offset, count);
     }
 
+    @Override
     public void setLength(long length) throws IOException {
         channel.truncate(length);
     }
 
+    @Override
     public void seek(long offset) throws IOException {
         channel.position(offset);
     }