diff --git a/src/org/kde/kdeconnect/Device.java b/src/org/kde/kdeconnect/Device.java
index ceb70426..f73dbb32 100644
--- a/src/org/kde/kdeconnect/Device.java
+++ b/src/org/kde/kdeconnect/Device.java
@@ -19,6 +19,7 @@ import android.util.Base64;
 import android.util.Log;
 
 import androidx.annotation.AnyThread;
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.WorkerThread;
 import androidx.core.app.NotificationCompat;
@@ -112,6 +113,7 @@ public class Device implements BaseLink.PacketReceiver {
             return Computer; //Default
         }
 
+        @NonNull
         public String toString() {
             switch (this) {
                 case Tablet:
diff --git a/src/org/kde/kdeconnect/Helpers/LongSummaryPreferenceCategory.java b/src/org/kde/kdeconnect/Helpers/LongSummaryPreferenceCategory.java
index 9b688e0d..9d35a315 100644
--- a/src/org/kde/kdeconnect/Helpers/LongSummaryPreferenceCategory.java
+++ b/src/org/kde/kdeconnect/Helpers/LongSummaryPreferenceCategory.java
@@ -10,6 +10,7 @@ import android.content.Context;
 import android.util.AttributeSet;
 import android.widget.TextView;
 
+import androidx.annotation.NonNull;
 import androidx.preference.PreferenceCategory;
 import androidx.preference.PreferenceViewHolder;
 
@@ -24,7 +25,7 @@ public class LongSummaryPreferenceCategory extends PreferenceCategory {
     }
 
     @Override
-    public void onBindViewHolder(PreferenceViewHolder holder) {
+    public void onBindViewHolder(@NonNull PreferenceViewHolder holder) {
         super.onBindViewHolder(holder);
         TextView summary = (TextView) holder.findViewById(android.R.id.summary);
         summary.setMaxLines(3);
diff --git a/src/org/kde/kdeconnect/Helpers/TelephonyHelper.java b/src/org/kde/kdeconnect/Helpers/TelephonyHelper.java
index 05efb15a..4d7174c2 100644
--- a/src/org/kde/kdeconnect/Helpers/TelephonyHelper.java
+++ b/src/org/kde/kdeconnect/Helpers/TelephonyHelper.java
@@ -420,6 +420,7 @@ public class TelephonyHelper {
            this.subscriptionID = subscriptionID;
        }
 
+        @NonNull
         @Override
         public String toString() {
             return number;
diff --git a/src/org/kde/kdeconnect/Plugins/SftpPlugin/SftpSettingsFragment.java b/src/org/kde/kdeconnect/Plugins/SftpPlugin/SftpSettingsFragment.java
index f45143bb..8d4311a7 100644
--- a/src/org/kde/kdeconnect/Plugins/SftpPlugin/SftpSettingsFragment.java
+++ b/src/org/kde/kdeconnect/Plugins/SftpPlugin/SftpSettingsFragment.java
@@ -128,8 +128,9 @@ public class SftpSettingsFragment
         }
     }
 
+    @NonNull
     @Override
-    protected RecyclerView.Adapter onCreateAdapter(PreferenceScreen preferenceScreen) {
+    protected RecyclerView.Adapter onCreateAdapter(@NonNull PreferenceScreen preferenceScreen) {
         if (savedActionModeState != null) {
             getListView().post(this::restoreActionMode);
         }
@@ -162,7 +163,7 @@ public class SftpSettingsFragment
     }
 
     @Override
-    public void onDisplayPreferenceDialog(Preference preference) {
+    public void onDisplayPreferenceDialog(@NonNull Preference preference) {
         if (preference instanceof StoragePreference) {
             StoragePreferenceDialogFragment fragment = StoragePreferenceDialogFragment.newInstance(preference.getKey());
             fragment.setTargetFragment(this, 0);
@@ -174,7 +175,7 @@ public class SftpSettingsFragment
     }
 
     @Override
-    public void onSaveInstanceState(Bundle outState) {
+    public void onSaveInstanceState(@NonNull Bundle outState) {
         super.onSaveInstanceState(outState);
 
         try {
@@ -340,7 +341,7 @@ public class SftpSettingsFragment
     }
 
     @Override
-    public boolean onPreferenceChange(Preference preference, Object newValue) {
+    public boolean onPreferenceChange(@NonNull Preference preference, Object newValue) {
         SftpPlugin.StorageInfo newStorageInfo = (SftpPlugin.StorageInfo) newValue;
 
         ListIterator<SftpPlugin.StorageInfo> it = storageInfoList.listIterator();
diff --git a/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreference.java b/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreference.java
index c356a5c8..76a7685c 100644
--- a/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreference.java
+++ b/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreference.java
@@ -96,7 +96,7 @@ public class StoragePreference extends DialogPreference {
     }
 
     @Override
-    public void onBindViewHolder(PreferenceViewHolder holder) {
+    public void onBindViewHolder(@NonNull PreferenceViewHolder holder) {
         super.onBindViewHolder(holder);
 
         checkbox = (CheckBox) holder.itemView.findViewById(R.id.checkbox);
diff --git a/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreferenceDialogFragment.java b/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreferenceDialogFragment.java
index 573110e3..b51234f8 100644
--- a/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreferenceDialogFragment.java
+++ b/src/org/kde/kdeconnect/Plugins/SftpPlugin/StoragePreferenceDialogFragment.java
@@ -104,7 +104,7 @@ public class StoragePreferenceDialogFragment extends PreferenceDialogFragmentCom
     }
 
     @Override
-    protected void onBindDialogView(View view) {
+    protected void onBindDialogView(@NonNull View view) {
         super.onBindDialogView(view);
 
         binding = FragmentStoragePreferenceDialogBinding.bind(view);
diff --git a/src/org/kde/kdeconnect/UserInterface/AlertDialogFragment.java b/src/org/kde/kdeconnect/UserInterface/AlertDialogFragment.java
index 00e42d02..de1ce766 100644
--- a/src/org/kde/kdeconnect/UserInterface/AlertDialogFragment.java
+++ b/src/org/kde/kdeconnect/UserInterface/AlertDialogFragment.java
@@ -100,7 +100,7 @@ public class AlertDialogFragment extends DialogFragment implements DialogInterfa
     }
 
     @Override
-    public void onCancel(DialogInterface dialog) {
+    public void onCancel(@NonNull DialogInterface dialog) {
         super.onCancel(dialog);
 
         if (callback != null) {
@@ -109,7 +109,7 @@ public class AlertDialogFragment extends DialogFragment implements DialogInterfa
     }
 
     @Override
-    public void onDismiss(DialogInterface dialog) {
+    public void onDismiss(@NonNull DialogInterface dialog) {
         super.onDismiss(dialog);
 
         if (callback != null) {
diff --git a/src/org/kde/kdeconnect/UserInterface/MainActivity.java b/src/org/kde/kdeconnect/UserInterface/MainActivity.java
index ae542d7a..ae72cc53 100644
--- a/src/org/kde/kdeconnect/UserInterface/MainActivity.java
+++ b/src/org/kde/kdeconnect/UserInterface/MainActivity.java
@@ -368,7 +368,7 @@ public class MainActivity extends AppCompatActivity implements SharedPreferences
     }
 
     @Override
-    protected void onSaveInstanceState(Bundle outState) {
+    protected void onSaveInstanceState(@NonNull Bundle outState) {
         super.onSaveInstanceState(outState);
         outState.putString(STATE_SELECTED_DEVICE, mCurrentDevice);
         outState.putInt(STATE_SELECTED_MENU_ENTRY, mCurrentMenuEntry);
diff --git a/src/org/kde/kdeconnect/UserInterface/PairingFragment.java b/src/org/kde/kdeconnect/UserInterface/PairingFragment.java
index 7b4b24c4..a6740835 100644
--- a/src/org/kde/kdeconnect/UserInterface/PairingFragment.java
+++ b/src/org/kde/kdeconnect/UserInterface/PairingFragment.java
@@ -130,7 +130,7 @@ public class PairingFragment extends Fragment implements PairingDeviceItem.Callb
     }
 
     @Override
-    public void onAttach(Context context) {
+    public void onAttach(@NonNull Context context) {
         super.onAttach(context);
         mActivity = ((MainActivity) getActivity());
     }
@@ -286,7 +286,7 @@ public class PairingFragment extends Fragment implements PairingDeviceItem.Callb
     }
 
     @Override
-    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
+    public void onCreateOptionsMenu(@NonNull Menu menu, MenuInflater inflater) {
         inflater.inflate(R.menu.pairing, menu);
     }
 
diff --git a/src/org/kde/kdeconnect/UserInterface/PluginPreference.java b/src/org/kde/kdeconnect/UserInterface/PluginPreference.java
index 1a2f0096..37a8ac8e 100644
--- a/src/org/kde/kdeconnect/UserInterface/PluginPreference.java
+++ b/src/org/kde/kdeconnect/UserInterface/PluginPreference.java
@@ -49,7 +49,7 @@ setIcon(android.R.color.transparent);
     }
 
     @Override
-    public void onBindViewHolder(PreferenceViewHolder holder) {
+    public void onBindViewHolder(@NonNull PreferenceViewHolder holder) {
         super.onBindViewHolder(holder);
 
         View.OnClickListener toggleListener = v -> {
diff --git a/src/org/kde/kdeconnect/UserInterface/PluginSettingsListFragment.java b/src/org/kde/kdeconnect/UserInterface/PluginSettingsListFragment.java
index fc77c159..ac058972 100644
--- a/src/org/kde/kdeconnect/UserInterface/PluginSettingsListFragment.java
+++ b/src/org/kde/kdeconnect/UserInterface/PluginSettingsListFragment.java
@@ -93,8 +93,9 @@ public class PluginSettingsListFragment extends PreferenceFragmentCompat {
         });
     }
 
+    @NonNull
     @Override
-    protected RecyclerView.Adapter onCreateAdapter(PreferenceScreen preferenceScreen) {
+    protected RecyclerView.Adapter onCreateAdapter(@NonNull PreferenceScreen preferenceScreen) {
         RecyclerView.Adapter adapter = super.onCreateAdapter(preferenceScreen);
 
         /*
@@ -144,7 +145,7 @@ public class PluginSettingsListFragment extends PreferenceFragmentCompat {
     }
 
     @Override
-    public void onSaveInstanceState(Bundle outState) {
+    public void onSaveInstanceState(@NonNull Bundle outState) {
         super.onSaveInstanceState(outState);
 
         Parcelable layoutManagerState = recyclerViewLayoutManagerState;
diff --git a/src/org/kde/kdeconnect/UserInterface/SettingsFragment.java b/src/org/kde/kdeconnect/UserInterface/SettingsFragment.java
index 9d2d2656..896d0be7 100644
--- a/src/org/kde/kdeconnect/UserInterface/SettingsFragment.java
+++ b/src/org/kde/kdeconnect/UserInterface/SettingsFragment.java
@@ -32,6 +32,7 @@ public class SettingsFragment extends PreferenceFragmentCompat {
 
     private EditTextPreference renameDevice;
 
+    @NonNull
     @Override
     public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
         if (getActivity() != null) {