diff --git a/app/src/main/java/com/owncloud/android/ui/adapter/OCFileListAdapter.java b/app/src/main/java/com/owncloud/android/ui/adapter/OCFileListAdapter.java
index 3544b988e5f9..9e6c4637f841 100644
--- a/app/src/main/java/com/owncloud/android/ui/adapter/OCFileListAdapter.java
+++ b/app/src/main/java/com/owncloud/android/ui/adapter/OCFileListAdapter.java
@@ -133,7 +133,7 @@ public class OCFileListAdapter extends RecyclerView.Adapter<RecyclerView.ViewHol
     private final long footerId = UUID.randomUUID().getLeastSignificantBits();
     private final long headerId = UUID.randomUUID().getLeastSignificantBits();
 
-    private List<OCFile> recommendedFiles = new ArrayList<>();
+    private final List<OCFile> recommendedFiles = new ArrayList<>();
     private RecommendedFilesAdapter recommendedFilesAdapter;
     private final OCFileListAdapterHelper helper = new OCFileListAdapterHelper();
     private final ThumbnailGenerator thumbnailGenerator;
@@ -189,7 +189,7 @@ public OCFileListAdapter(
 
         setHasStableIds(true);
 
-        // initialise thumbnails cache on background thread
+        // initialize thumbnails cache on background thread
         ThumbnailsCacheManager.initDiskCacheAsync();
         isRTL = DisplayUtils.isRTL();
     }
@@ -936,6 +936,7 @@ public void setSortOrder(@Nullable OCFile folder, @NonNull FileSortOrder sortOrd
         this.sortOrder = sortOrder;
     }
 
+    @NonNull
     public Set<OCFile> getCheckedItems() {
         return ocFileListDelegate.getCheckedItems();
     }
@@ -997,15 +998,15 @@ public boolean shouldCallGeneratedCallback(String tag, Object callContext) {
         return ((ImageView) callContext).getTag().equals(tag);
     }
 
-    public boolean isCheckedFile(OCFile file) {
+    public boolean isCheckedFile(@NonNull OCFile file) {
         return ocFileListDelegate.isCheckedFile(file);
     }
 
-    public void addCheckedFile(OCFile file) {
+    public void addCheckedFile(@NonNull OCFile file) {
         ocFileListDelegate.addCheckedFile(file);
     }
 
-    public void setHighlightedItem(OCFile file) {
+    public void setHighlightedItem(@NonNull OCFile file) {
         ocFileListDelegate.setHighlightedItem(file);
     }
 
@@ -1023,7 +1024,7 @@ public void setShowMetadata(boolean bool) {
 
     @NonNull
     @Override
-    public String getPopupText(View view, int position) {
+    public String getPopupText(@NonNull View view, int position) {
         OCFile file = getItem(position);
 
         if (file == null || sortOrder == null) {
@@ -1073,7 +1074,8 @@ public void setCurrentDirectory(OCFile folder) {
     // payload only for local file indicator
     @Override
     public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position, @NonNull List<Object> payloads) {
-        if (!payloads.isEmpty() && payloads.get(0) instanceof Integer iconId && holder instanceof ListViewHolder listViewHolder) {
+        if (!payloads.isEmpty() && payloads.get(0) instanceof Integer iconId && 
+            holder instanceof ListViewHolder listViewHolder) {
             listViewHolder.getLocalFileIndicator().setImageResource(iconId);
             listViewHolder.getLocalFileIndicator().setVisibility(View.VISIBLE);
             // skip full rebind
diff --git a/app/src/main/java/com/owncloud/android/ui/fragment/OCFileListFragment.java b/app/src/main/java/com/owncloud/android/ui/fragment/OCFileListFragment.java
index f8d2549f7034..31cdbeb107ec 100644
--- a/app/src/main/java/com/owncloud/android/ui/fragment/OCFileListFragment.java
+++ b/app/src/main/java/com/owncloud/android/ui/fragment/OCFileListFragment.java
@@ -241,7 +241,7 @@ protected enum MenuItemAddRemove {
 
     protected MenuItemAddRemove menuItemAddRemoveValue = MenuItemAddRemove.ADD_GRID_AND_SORT_WITH_SEARCH;
 
-    private List<MenuItem> mOriginalMenuItems = new ArrayList<>();
+    private final List<MenuItem> mOriginalMenuItems = new ArrayList<>();
 
     private static OCFileDepth fileDepth = OCFileDepth.Root;
 
@@ -311,14 +311,14 @@ public void onAttach(@NonNull Context context) {
         try {
             mContainerActivity = (FileFragment.ContainerActivity) context;
         } catch (ClassCastException e) {
-            throw new IllegalArgumentException(context.toString() + " must implement " +
+            throw new IllegalArgumentException(context + " must implement " +
                                                    FileFragment.ContainerActivity.class.getSimpleName(), e);
         }
         try {
             setOnRefreshListener((OnEnforceableRefreshListener) context);
 
         } catch (ClassCastException e) {
-            throw new IllegalArgumentException(context.toString() + " must implement " +
+            throw new IllegalArgumentException(context + " must implement " +
                                                    OnEnforceableRefreshListener.class.getSimpleName(), e);
         }
     }
@@ -577,7 +577,7 @@ public void uploadFromApp() {
         action = action.setType("*/*").addCategory(Intent.CATEGORY_OPENABLE);
         action.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true);
 
-        getActivity().startActivityForResult(
+        requireActivity().startActivityForResult(
             Intent.createChooser(action, getString(R.string.upload_chooser_title)),
             FileDisplayActivity.REQUEST_CODE__SELECT_CONTENT_FROM_APPS
                                             );
@@ -767,8 +767,9 @@ public void onHeaderClicked() {
     }
 
     @Override
-    public void showTemplate(@NonNull Creator creator, @NonNull String headline) {
-        ChooseTemplateDialogFragment.newInstance(mFile, creator, headline).show(requireActivity().getSupportFragmentManager(),
+    public void showTemplate(Creator creator, String headline) {
+        ChooseTemplateDialogFragment.newInstance(mFile, creator, headline).show(requireActivity()
+                                                                                    .getSupportFragmentManager(), 
                                                                                 DIALOG_CREATE_DOCUMENT);
     }
 
@@ -910,7 +911,9 @@ public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
             final int checkedCount = checkedFiles.size();
 
             if (mActiveActionMode != null) {
-                String title = getResources().getQuantityString(R.plurals.items_selected_count, checkedCount, checkedCount);
+                String title = getResources().getQuantityString(R.plurals.items_selected_count, 
+                                                                checkedCount, 
+                                                                checkedCount);
                 mActiveActionMode.setTitle(title);
             }
 
@@ -984,7 +987,7 @@ protected void setChoiceModeAsMultipleModal(Bundle savedInstanceState) {
         if (savedInstanceState != null) {
             mMultiChoiceModeListener.loadStateFrom(savedInstanceState);
         }
-        ((FileActivity) getActivity()).addDrawerListener(mMultiChoiceModeListener);
+        ((FileActivity) requireActivity()).addDrawerListener(mMultiChoiceModeListener);
     }
 
     /**
@@ -1132,7 +1135,9 @@ public boolean onLongItemClicked(OCFile file) {
 
     private void folderOnItemClick(OCFile file, int position) {
         if (requireActivity() instanceof FolderPickerActivity fpa) {
-            String filenameErrorMessage = FileNameValidator.INSTANCE.checkFileName(file.getFileName(), getCapabilities(), requireContext());
+            String filenameErrorMessage = FileNameValidator.INSTANCE.checkFileName(file.getFileName(), 
+                                                                                   getCapabilities(), 
+                                                                                   requireContext());
             if (filenameErrorMessage != null) {
                 DisplayUtils.showSnackMessage(fpa, filenameErrorMessage);
                 return;
@@ -1329,7 +1334,7 @@ public boolean onFileActionChosen(@IdRes final int itemId, Set<OCFile> checkedFi
                 return true;
             } else if (itemId == R.id.action_rename_file) {
                 RenameFileDialogFragment dialog = RenameFileDialogFragment.newInstance(singleFile, mFile);
-                dialog.show(getFragmentManager(), FileDetailFragment.FTAG_RENAME_FILE);
+                dialog.show(requireFragmentManager(), FileDetailFragment.FTAG_RENAME_FILE);
                 return true;
             } else if (itemId == R.id.action_see_details) {
                 if (mActiveActionMode != null) {
@@ -1368,7 +1373,7 @@ public boolean onFileActionChosen(@IdRes final int itemId, Set<OCFile> checkedFi
         if (itemId == R.id.action_remove_file) {
             RemoveFilesDialogFragment dialog =
                 RemoveFilesDialogFragment.newInstance(new ArrayList<>(checkedFiles), mActiveActionMode);
-            dialog.show(getFragmentManager(), ConfirmationDialogFragment.FTAG_CONFIRMATION);
+            dialog.show(requireFragmentManager(), ConfirmationDialogFragment.FTAG_CONFIRMATION);
             return true;
         } else if (itemId == R.id.action_download_file || itemId == R.id.action_sync_file) {
             syncAndCheckFiles(checkedFiles);
@@ -1462,7 +1467,7 @@ private void pickFolderForMoveOrCopy(final Set<OCFile> checkedFiles) {
         action.putExtra(FolderPickerActivity.EXTRA_FOLDER, getCurrentFile());
         action.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION); // No animation since we stay in the same folder
         action.putExtra(FolderPickerActivity.EXTRA_ACTION, extraAction);
-        getActivity().startActivityForResult(action, requestCode);
+        requireActivity().startActivityForResult(action, requestCode);
     }