diff --git a/app/src/main/java/org/schabi/newpipe/fragments/list/channel/ChannelFragment.java b/app/src/main/java/org/schabi/newpipe/fragments/list/channel/ChannelFragment.java
index 9a52b8d12..562ee7f0d 100644
--- a/app/src/main/java/org/schabi/newpipe/fragments/list/channel/ChannelFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/fragments/list/channel/ChannelFragment.java
@@ -90,8 +90,6 @@ public class ChannelFragment extends BaseListInfoFragment<ChannelInfo> {
 
     private MenuItem menuRssButton;
 
-    private boolean mIsVisibleToUser = false;
-
     public static ChannelFragment getInstance(int serviceId, String url, String name) {
         ChannelFragment instance = new ChannelFragment();
         instance.setInitialData(serviceId, url, name);
@@ -105,7 +103,7 @@ public class ChannelFragment extends BaseListInfoFragment<ChannelInfo> {
     @Override
     public void setUserVisibleHint(boolean isVisibleToUser) {
         super.setUserVisibleHint(isVisibleToUser);
-        mIsVisibleToUser = isVisibleToUser;
+        boolean mIsVisibleToUser = isVisibleToUser;
         if(activity != null
                 && useAsFrontPage
                 && isVisibleToUser) {
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 a699e28bc..b7831d4ab 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
@@ -122,7 +122,6 @@ public class SearchFragment
     private String nextPageUrl;
     private String contentCountry;
     private boolean isSuggestionsEnabled = true;
-    private boolean isSearchHistoryEnabled = true;
 
     private PublishSubject<String> suggestionPublisher = PublishSubject.create();
     private Disposable searchDisposable;
@@ -173,7 +172,7 @@ public class SearchFragment
 
         suggestionListAdapter = new SuggestionListAdapter(activity);
         SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(activity);
-        isSearchHistoryEnabled = preferences.getBoolean(getString(R.string.enable_search_history_key), true);
+        boolean isSearchHistoryEnabled = preferences.getBoolean(getString(R.string.enable_search_history_key), true);
         suggestionListAdapter.setShowSuggestionHistory(isSearchHistoryEnabled);
 
         historyRecordManager = new HistoryRecordManager(context);
diff --git a/app/src/main/java/org/schabi/newpipe/local/subscription/SubscriptionFragment.java b/app/src/main/java/org/schabi/newpipe/local/subscription/SubscriptionFragment.java
index d8a26f0eb..69852b809 100644
--- a/app/src/main/java/org/schabi/newpipe/local/subscription/SubscriptionFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/local/subscription/SubscriptionFragment.java
@@ -81,7 +81,6 @@ public class SubscriptionFragment extends BaseStateFragment<List<SubscriptionEnt
     protected Parcelable itemsListState;
     private InfoListAdapter infoListAdapter;
 
-    private View headerRootLayout;
     private View whatsNewItemListHeader;
     private View importExportListHeader;
 
@@ -291,6 +290,7 @@ public class SubscriptionFragment extends BaseStateFragment<List<SubscriptionEnt
         itemsList = rootView.findViewById(R.id.items_list);
         itemsList.setLayoutManager(new LinearLayoutManager(activity));
 
+        View headerRootLayout;
         infoListAdapter.setHeader(headerRootLayout = activity.getLayoutInflater().inflate(R.layout.subscription_header, itemsList, false));
         whatsNewItemListHeader = headerRootLayout.findViewById(R.id.whats_new);
         importExportListHeader = headerRootLayout.findViewById(R.id.import_export);
diff --git a/app/src/main/java/org/schabi/newpipe/player/PopupVideoPlayer.java b/app/src/main/java/org/schabi/newpipe/player/PopupVideoPlayer.java
index 0e7328020..a36a0576c 100644
--- a/app/src/main/java/org/schabi/newpipe/player/PopupVideoPlayer.java
+++ b/app/src/main/java/org/schabi/newpipe/player/PopupVideoPlayer.java
@@ -114,7 +114,6 @@ public final class PopupVideoPlayer extends Service {
 
     private View closeOverlayView;
     private FloatingActionButton closeOverlayButton;
-    private WindowManager.LayoutParams closeOverlayLayoutParams;
 
     private int tossFlingVelocity;
 
@@ -248,7 +247,7 @@ public final class PopupVideoPlayer extends Service {
         final int flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                 | WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM;
 
-        closeOverlayLayoutParams = new WindowManager.LayoutParams(
+        WindowManager.LayoutParams closeOverlayLayoutParams = new WindowManager.LayoutParams(
                 ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT,
                 layoutParamType,
                 flags,
diff --git a/app/src/main/java/org/schabi/newpipe/player/helper/PlaybackParameterDialog.java b/app/src/main/java/org/schabi/newpipe/player/helper/PlaybackParameterDialog.java
index d6453f579..f49ca3330 100644
--- a/app/src/main/java/org/schabi/newpipe/player/helper/PlaybackParameterDialog.java
+++ b/app/src/main/java/org/schabi/newpipe/player/helper/PlaybackParameterDialog.java
@@ -66,25 +66,15 @@ public class PlaybackParameterDialog extends DialogFragment {
     private double stepSize = DEFAULT_STEP;
 
     @Nullable private SeekBar tempoSlider;
-    @Nullable private TextView tempoMinimumText;
-    @Nullable private TextView tempoMaximumText;
     @Nullable private TextView tempoCurrentText;
     @Nullable private TextView tempoStepDownText;
     @Nullable private TextView tempoStepUpText;
 
     @Nullable private SeekBar pitchSlider;
-    @Nullable private TextView pitchMinimumText;
-    @Nullable private TextView pitchMaximumText;
     @Nullable private TextView pitchCurrentText;
     @Nullable private TextView pitchStepDownText;
     @Nullable private TextView pitchStepUpText;
 
-    @Nullable private TextView stepSizeOnePercentText;
-    @Nullable private TextView stepSizeFivePercentText;
-    @Nullable private TextView stepSizeTenPercentText;
-    @Nullable private TextView stepSizeTwentyFivePercentText;
-    @Nullable private TextView stepSizeOneHundredPercentText;
-
     @Nullable private CheckBox unhookingCheckbox;
     @Nullable private CheckBox skipSilenceCheckbox;
 
@@ -181,8 +171,8 @@ public class PlaybackParameterDialog extends DialogFragment {
 
     private void setupTempoControl(@NonNull View rootView) {
         tempoSlider = rootView.findViewById(R.id.tempoSeekbar);
-        tempoMinimumText = rootView.findViewById(R.id.tempoMinimumText);
-        tempoMaximumText = rootView.findViewById(R.id.tempoMaximumText);
+        TextView tempoMinimumText = rootView.findViewById(R.id.tempoMinimumText);
+        TextView tempoMaximumText = rootView.findViewById(R.id.tempoMaximumText);
         tempoCurrentText = rootView.findViewById(R.id.tempoCurrentText);
         tempoStepUpText = rootView.findViewById(R.id.tempoStepUp);
         tempoStepDownText = rootView.findViewById(R.id.tempoStepDown);
@@ -203,8 +193,8 @@ public class PlaybackParameterDialog extends DialogFragment {
 
     private void setupPitchControl(@NonNull View rootView) {
         pitchSlider = rootView.findViewById(R.id.pitchSeekbar);
-        pitchMinimumText = rootView.findViewById(R.id.pitchMinimumText);
-        pitchMaximumText = rootView.findViewById(R.id.pitchMaximumText);
+        TextView pitchMinimumText = rootView.findViewById(R.id.pitchMinimumText);
+        TextView pitchMaximumText = rootView.findViewById(R.id.pitchMaximumText);
         pitchCurrentText = rootView.findViewById(R.id.pitchCurrentText);
         pitchStepDownText = rootView.findViewById(R.id.pitchStepDown);
         pitchStepUpText = rootView.findViewById(R.id.pitchStepUp);
@@ -247,11 +237,11 @@ public class PlaybackParameterDialog extends DialogFragment {
     }
 
     private void setupStepSizeSelector(@NonNull final View rootView) {
-        stepSizeOnePercentText = rootView.findViewById(R.id.stepSizeOnePercent);
-        stepSizeFivePercentText = rootView.findViewById(R.id.stepSizeFivePercent);
-        stepSizeTenPercentText = rootView.findViewById(R.id.stepSizeTenPercent);
-        stepSizeTwentyFivePercentText = rootView.findViewById(R.id.stepSizeTwentyFivePercent);
-        stepSizeOneHundredPercentText = rootView.findViewById(R.id.stepSizeOneHundredPercent);
+        TextView stepSizeOnePercentText = rootView.findViewById(R.id.stepSizeOnePercent);
+        TextView stepSizeFivePercentText = rootView.findViewById(R.id.stepSizeFivePercent);
+        TextView stepSizeTenPercentText = rootView.findViewById(R.id.stepSizeTenPercent);
+        TextView stepSizeTwentyFivePercentText = rootView.findViewById(R.id.stepSizeTwentyFivePercent);
+        TextView stepSizeOneHundredPercentText = rootView.findViewById(R.id.stepSizeOneHundredPercent);
 
         if (stepSizeOnePercentText != null) {
             stepSizeOnePercentText.setText(getPercentString(STEP_ONE_PERCENT_VALUE));
diff --git a/app/src/main/java/org/schabi/newpipe/report/ErrorActivity.java b/app/src/main/java/org/schabi/newpipe/report/ErrorActivity.java
index 3ad08c3ec..3790d6651 100644
--- a/app/src/main/java/org/schabi/newpipe/report/ErrorActivity.java
+++ b/app/src/main/java/org/schabi/newpipe/report/ErrorActivity.java
@@ -81,12 +81,7 @@ public class ErrorActivity extends AppCompatActivity {
     private ErrorInfo errorInfo;
     private Class returnActivity;
     private String currentTimeStamp;
-    // views
-    private TextView errorView;
     private EditText userCommentBox;
-    private Button reportButton;
-    private TextView infoView;
-    private TextView errorMessageView;
 
     public static void reportUiError(final AppCompatActivity activity, final Throwable el) {
         reportError(activity, el, activity.getClass(), null,
@@ -194,11 +189,11 @@ public class ErrorActivity extends AppCompatActivity {
             actionBar.setDisplayShowTitleEnabled(true);
         }
 
-        reportButton = findViewById(R.id.errorReportButton);
+        Button reportButton = findViewById(R.id.errorReportButton);
         userCommentBox = findViewById(R.id.errorCommentBox);
-        errorView = findViewById(R.id.errorView);
-        infoView = findViewById(R.id.errorInfosView);
-        errorMessageView = findViewById(R.id.errorMessageView);
+        TextView errorView = findViewById(R.id.errorView);
+        TextView infoView = findViewById(R.id.errorInfosView);
+        TextView errorMessageView = findViewById(R.id.errorMessageView);
 
         ActivityCommunicator ac = ActivityCommunicator.getCommunicator();
         returnActivity = ac.returnActivity;
diff --git a/app/src/main/java/org/schabi/newpipe/settings/ContentSettingsFragment.java b/app/src/main/java/org/schabi/newpipe/settings/ContentSettingsFragment.java
index ca48ed8b5..5f02dd785 100644
--- a/app/src/main/java/org/schabi/newpipe/settings/ContentSettingsFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/settings/ContentSettingsFragment.java
@@ -47,7 +47,6 @@ public class ContentSettingsFragment extends BasePreferenceFragment {
     private static final int REQUEST_IMPORT_PATH = 8945;
     private static final int REQUEST_EXPORT_PATH = 30945;
 
-    private String homeDir;
     private File databasesDir;
     private File newpipe_db;
     private File newpipe_db_journal;
@@ -81,7 +80,7 @@ public class ContentSettingsFragment extends BasePreferenceFragment {
     @Override
     public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
 
-        homeDir = getActivity().getApplicationInfo().dataDir;
+        String homeDir = getActivity().getApplicationInfo().dataDir;
         databasesDir = new File(homeDir + "/databases");
         newpipe_db = new File(homeDir + "/databases/newpipe.db");
         newpipe_db_journal = new File(homeDir + "/databases/newpipe.db-journal");
diff --git a/app/src/main/java/org/schabi/newpipe/settings/SelectChannelFragment.java b/app/src/main/java/org/schabi/newpipe/settings/SelectChannelFragment.java
index 6d85d5967..c1b2f1703 100644
--- a/app/src/main/java/org/schabi/newpipe/settings/SelectChannelFragment.java
+++ b/app/src/main/java/org/schabi/newpipe/settings/SelectChannelFragment.java
@@ -51,8 +51,6 @@ import io.reactivex.schedulers.Schedulers;
  */
 
 public class SelectChannelFragment extends DialogFragment {
-    private SelectChannelAdapter channelAdapter;
-    private SubscriptionService subscriptionService;
     private ImageLoader imageLoader = ImageLoader.getInstance();
 
     private ProgressBar progressBar;
@@ -91,7 +89,7 @@ public class SelectChannelFragment extends DialogFragment {
         View v = inflater.inflate(R.layout.select_channel_fragment, container, false);
         recyclerView = v.findViewById(R.id.items_list);
         recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
-        channelAdapter = new SelectChannelAdapter();
+        SelectChannelAdapter channelAdapter = new SelectChannelAdapter();
         recyclerView.setAdapter(channelAdapter);
 
         progressBar = v.findViewById(R.id.progressBar);
@@ -101,7 +99,7 @@ public class SelectChannelFragment extends DialogFragment {
         emptyView.setVisibility(View.GONE);
 
 
-        subscriptionService = SubscriptionService.getInstance(getContext());
+        SubscriptionService subscriptionService = SubscriptionService.getInstance(getContext());
         subscriptionService.getSubscription().toObservable()
                 .subscribeOn(Schedulers.io())
                 .observeOn(AndroidSchedulers.mainThread())