diff --git a/.idea/misc.xml b/.idea/misc.xml
index 9f569f1..4b5f46f 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="NullableNotNullManager">
-    <option name="myDefaultNullable" value="android.support.annotation.Nullable" />
-    <option name="myDefaultNotNull" value="android.support.annotation.NonNull" />
+    <option name="myDefaultNullable" value="androidx.annotation.Nullable" />
+    <option name="myDefaultNotNull" value="androidx.annotation.NonNull" />
     <option name="myNullables">
       <value>
         <list size="12">
diff --git a/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/DevicesFragment.java b/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/DevicesFragment.java
index 3a057f9..8e1a471 100644
--- a/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/DevicesFragment.java
+++ b/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/DevicesFragment.java
@@ -5,6 +5,8 @@ import android.content.Context;
 import android.hardware.usb.UsbDevice;
 import android.hardware.usb.UsbManager;
 import android.os.Bundle;
+
+import androidx.annotation.NonNull;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.ListFragment;
 import android.view.Menu;
@@ -25,7 +27,7 @@ import java.util.Locale;
 
 public class DevicesFragment extends ListFragment {
 
-    class ListItem {
+    static class ListItem {
         UsbDevice device;
         int port;
         UsbSerialDriver driver;
@@ -37,7 +39,7 @@ public class DevicesFragment extends ListFragment {
         }
     }
 
-    private ArrayList<ListItem> listItems = new ArrayList<>();
+    private final ArrayList<ListItem> listItems = new ArrayList<>();
     private ArrayAdapter<ListItem> listAdapter;
     private int baudRate = 19200;
     private boolean withIoManager = true;
@@ -47,8 +49,9 @@ public class DevicesFragment extends ListFragment {
         super.onCreate(savedInstanceState);
         setHasOptionsMenu(true);
         listAdapter = new ArrayAdapter<ListItem>(getActivity(), 0, listItems) {
+            @NonNull
             @Override
-            public View getView(int position, View view, ViewGroup parent) {
+            public View getView(int position, View view, @NonNull ViewGroup parent) {
                 ListItem item = listItems.get(position);
                 if (view == null)
                     view = getActivity().getLayoutInflater().inflate(R.layout.device_list_item, parent, false);
@@ -78,7 +81,7 @@ public class DevicesFragment extends ListFragment {
     }
 
     @Override
-    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
+    public void onCreateOptionsMenu(@NonNull Menu menu, MenuInflater inflater) {
         inflater.inflate(R.menu.menu_devices, menu);
     }
 
@@ -142,7 +145,7 @@ public class DevicesFragment extends ListFragment {
     }
 
     @Override
-    public void onListItemClick(ListView l, View v, int position, long id) {
+    public void onListItemClick(@NonNull ListView l, @NonNull View v, int position, long id) {
         ListItem item = listItems.get(position-1);
         if(item.driver == null) {
             Toast.makeText(getActivity(), "no driver", Toast.LENGTH_SHORT).show();
diff --git a/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/MainActivity.java b/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/MainActivity.java
index 27d88e5..4dd5308 100644
--- a/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/MainActivity.java
+++ b/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/MainActivity.java
@@ -34,7 +34,7 @@ public class MainActivity extends AppCompatActivity implements FragmentManager.O
 
     @Override
     protected void onNewIntent(Intent intent) {
-        if(intent.getAction().equals("android.hardware.usb.action.USB_DEVICE_ATTACHED")) {
+        if("android.hardware.usb.action.USB_DEVICE_ATTACHED".equals(intent.getAction())) {
             TerminalFragment terminal = (TerminalFragment)getSupportFragmentManager().findFragmentByTag("terminal");
             if (terminal != null)
                 terminal.status("USB device detected");
diff --git a/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/TerminalFragment.java b/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/TerminalFragment.java
index 25275ff..1b15f18 100644
--- a/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/TerminalFragment.java
+++ b/usbSerialExamples/src/main/java/com/hoho/android/usbserial/examples/TerminalFragment.java
@@ -42,7 +42,7 @@ import java.util.concurrent.Executors;
 
 public class TerminalFragment extends Fragment implements SerialInputOutputManager.Listener {
 
-    private enum UsbPermission { Unknown, Requested, Granted, Denied };
+    private enum UsbPermission { Unknown, Requested, Granted, Denied }
 
     private static final String INTENT_ACTION_GRANT_USB = BuildConfig.APPLICATION_ID + ".GRANT_USB";
     private static final int WRITE_WAIT_MILLIS = 2000;
@@ -51,8 +51,8 @@ public class TerminalFragment extends Fragment implements SerialInputOutputManag
     private int deviceId, portNum, baudRate;
     private boolean withIoManager;
 
-    private BroadcastReceiver broadcastReceiver;
-    private Handler mainLooper;
+    private final BroadcastReceiver broadcastReceiver;
+    private final Handler mainLooper;
     private TextView receiveText;
     private ControlLines controlLines;
 
@@ -65,7 +65,7 @@ public class TerminalFragment extends Fragment implements SerialInputOutputManag
         broadcastReceiver = new BroadcastReceiver() {
             @Override
             public void onReceive(Context context, Intent intent) {
-                if(intent.getAction().equals(INTENT_ACTION_GRANT_USB)) {
+                if(INTENT_ACTION_GRANT_USB.equals(intent.getAction())) {
                     usbPermission = intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)
                             ? UsbPermission.Granted : UsbPermission.Denied;
                     connect();
@@ -258,10 +258,10 @@ public class TerminalFragment extends Fragment implements SerialInputOutputManag
             return;
         }
         try {
-            byte[] data = (str + '\n').getBytes();
+        byte[] data = (str + '\n').getBytes();
             SpannableStringBuilder spn = new SpannableStringBuilder();
             spn.append("send " + data.length + " bytes\n");
-            spn.append(HexDump.dumpHexString(data)+"\n");
+            spn.append(HexDump.dumpHexString(data)).append("\n");
             spn.setSpan(new ForegroundColorSpan(getResources().getColor(R.color.colorSendText)), 0, spn.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
             receiveText.append(spn);
             usbSerialPort.write(data, WRITE_WAIT_MILLIS);
@@ -291,7 +291,7 @@ public class TerminalFragment extends Fragment implements SerialInputOutputManag
         SpannableStringBuilder spn = new SpannableStringBuilder();
         spn.append("receive " + data.length + " bytes\n");
         if(data.length > 0)
-            spn.append(HexDump.dumpHexString(data)+"\n");
+            spn.append(HexDump.dumpHexString(data)).append("\n");
         receiveText.append(spn);
     }
 
@@ -304,8 +304,8 @@ public class TerminalFragment extends Fragment implements SerialInputOutputManag
     class ControlLines {
         private static final int refreshInterval = 200; // msec
 
-        private Runnable runnable;
-        private ToggleButton rtsBtn, ctsBtn, dtrBtn, dsrBtn, cdBtn, riBtn;
+        private final Runnable runnable;
+        private final ToggleButton rtsBtn, ctsBtn, dtrBtn, dsrBtn, cdBtn, riBtn;
 
         ControlLines(View view) {
             runnable = this::run; // w/o explicit Runnable, a new lambda would be created on each postDelayed, which would not be found again by removeCallbacks
diff --git a/usbSerialForAndroid/build.gradle b/usbSerialForAndroid/build.gradle
index d0a334b..9d94931 100644
--- a/usbSerialForAndroid/build.gradle
+++ b/usbSerialForAndroid/build.gradle
@@ -22,7 +22,7 @@ android {
 }
 
 dependencies {
-    implementation "androidx.annotation:annotation:1.1.0"
+    implementation "androidx.annotation:annotation:1.2.0"
     testImplementation 'junit:junit:4.13.2'
     testImplementation 'org.mockito:mockito-core:1.10.19'
     androidTestImplementation 'com.android.support.test:runner:1.0.2'
diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
index 9388b86..630ae4f 100644
--- a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
@@ -142,7 +142,7 @@ public class DeviceTest {
     }
 
     private static class TestBuffer {
-        private byte[] buf;
+        private final byte[] buf;
         private int len;
 
         private TestBuffer(int length) {
@@ -937,7 +937,7 @@ public class DeviceTest {
         int purgeTimeout = 250;
         TestBuffer tbuf;
         long begin;
-        int duration1, duration2, retries, i, timeout;
+        int duration1, duration2, retries, i;
         retries = purge ? 10 : 1;
         tbuf = new TestBuffer(writeBufferSize);
 
@@ -1260,7 +1260,7 @@ public class DeviceTest {
         usb.setParameters(2400, 8, 1, UsbSerialPort.PARITY_NONE);
         telnet.setParameters(2400, 8, 1, UsbSerialPort.PARITY_NONE);
         byte[] buf = new byte[64];
-        for(int i=0; i<buf.length; i++) buf[i]='a';
+        Arrays.fill(buf, (byte) 'a');
         StringBuilder data = new StringBuilder();
 
         usb.write(buf);
@@ -1449,17 +1449,14 @@ public class DeviceTest {
     public void readTimeout() throws Exception {
         final Boolean[] closed = {Boolean.FALSE};
 
-        Runnable closeThread = new Runnable() {
-            @Override
-            public void run() {
-            try {
-                Thread.sleep(100);
-            } catch (InterruptedException e) {
-                e.printStackTrace();
-            }
-            usb.close();
-            closed[0] = true;
-            }
+        Runnable closeThread = () -> {
+        try {
+            Thread.sleep(100);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        usb.close();
+        closed[0] = true;
         };
 
         usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_IOMANAGER_THREAD));
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java
index a34561e..37a7064 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java
@@ -287,7 +287,7 @@ public class CdcAcmSerialDriver implements UsbSerialDriver {
     }
 
     public static Map<Integer, int[]> getSupportedDevices() {
-        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<Integer, int[]>();
+        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<>();
         supportedDevices.put(UsbId.VENDOR_ARDUINO,
                 new int[] {
                         UsbId.ARDUINO_UNO,
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java
index 2b25a20..c0154f6 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Ch34xSerialDriver.java
@@ -363,7 +363,7 @@ public class Ch34xSerialDriver implements UsbSerialDriver {
 	}
 
 	public static Map<Integer, int[]> getSupportedDevices() {
-		final Map<Integer, int[]> supportedDevices = new LinkedHashMap<Integer, int[]>();
+		final Map<Integer, int[]> supportedDevices = new LinkedHashMap<>();
 		supportedDevices.put(UsbId.VENDOR_QINHENG, new int[]{
 				UsbId.QINHENG_CH340,
 				UsbId.QINHENG_CH341A,
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Cp21xxSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Cp21xxSerialDriver.java
index e6dcd25..189112c 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Cp21xxSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/Cp21xxSerialDriver.java
@@ -322,7 +322,7 @@ public class Cp21xxSerialDriver implements UsbSerialDriver {
     }
 
     public static Map<Integer, int[]> getSupportedDevices() {
-        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<Integer, int[]>();
+        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<>();
         supportedDevices.put(UsbId.VENDOR_SILABS,
                 new int[] {
             UsbId.SILABS_CP2102, // same ID for CP2101, CP2103, CP2104, CP2109
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/FtdiSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/FtdiSerialDriver.java
index 239355d..dbbc01c 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/FtdiSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/FtdiSerialDriver.java
@@ -415,7 +415,7 @@ public class FtdiSerialDriver implements UsbSerialDriver {
     }
 
     public static Map<Integer, int[]> getSupportedDevices() {
-        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<Integer, int[]>();
+        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<>();
         supportedDevices.put(UsbId.VENDOR_FTDI,
                 new int[] {
                     UsbId.FTDI_FT232R,
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProbeTable.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProbeTable.java
index bc2f310..615e046 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProbeTable.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProbeTable.java
@@ -21,7 +21,7 @@ import java.util.Map;
 public class ProbeTable {
 
     private final Map<Pair<Integer, Integer>, Class<? extends UsbSerialDriver>> mProbeTable =
-            new LinkedHashMap<Pair<Integer,Integer>, Class<? extends UsbSerialDriver>>();
+            new LinkedHashMap<>();
 
     /**
      * Adds or updates a (vendor, product) pair in the table.
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java
index 3659612..a61b01a 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java
@@ -35,7 +35,7 @@ public class ProlificSerialDriver implements UsbSerialDriver {
             28800, 38400, 57600, 115200, 128000, 134400, 161280, 201600, 230400, 268800,
             403200, 460800, 614400, 806400, 921600, 1228800, 2457600, 3000000, 6000000
     };
-    private enum DeviceType { DEVICE_TYPE_01, DEVICE_TYPE_HX};
+    private enum DeviceType { DEVICE_TYPE_01, DEVICE_TYPE_HX}
 
     private final UsbDevice mDevice;
     private final UsbSerialPort mPort;
@@ -502,7 +502,7 @@ public class ProlificSerialDriver implements UsbSerialDriver {
     }
 
     public static Map<Integer, int[]> getSupportedDevices() {
-        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<Integer, int[]>();
+        final Map<Integer, int[]> supportedDevices = new LinkedHashMap<>();
         supportedDevices.put(UsbId.VENDOR_PROLIFIC,
                 new int[] { UsbId.PROLIFIC_PL2303, });
         return supportedDevices;
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/UsbSerialProber.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/UsbSerialProber.java
index 854d019..d6b4dd7 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/UsbSerialProber.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/UsbSerialProber.java
@@ -46,11 +46,11 @@ public class UsbSerialProber {
      * not require permission from the Android USB system, since it does not
      * open any of the devices.
      *
-     * @param usbManager
+     * @param usbManager usb manager
      * @return a list, possibly empty, of all compatible drivers
      */
     public List<UsbSerialDriver> findAllDrivers(final UsbManager usbManager) {
-        final List<UsbSerialDriver> result = new ArrayList<UsbSerialDriver>();
+        final List<UsbSerialDriver> result = new ArrayList<>();
 
         for (final UsbDevice usbDevice : usbManager.getDeviceList().values()) {
             final UsbSerialDriver driver = probeDevice(usbDevice);
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/util/SerialInputOutputManager.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/util/SerialInputOutputManager.java
index aae3e58..ed7f0ae 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/util/SerialInputOutputManager.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/util/SerialInputOutputManager.java
@@ -52,12 +52,12 @@ public class SerialInputOutputManager implements Runnable {
         /**
          * Called when new incoming data is available.
          */
-        public void onNewData(byte[] data);
+        void onNewData(byte[] data);
 
         /**
          * Called when {@link SerialInputOutputManager#run()} aborts due to an error.
          */
-        public void onRunError(Exception e);
+        void onRunError(Exception e);
     }
 
     public SerialInputOutputManager(UsbSerialPort serialPort) {
@@ -200,7 +200,7 @@ public class SerialInputOutputManager implements Runnable {
 
     private void step() throws IOException {
         // Handle incoming data.
-        byte[] buffer = null;
+        byte[] buffer;
         synchronized (mReadBufferLock) {
             buffer = mReadBuffer.array();
         }
diff --git a/usbSerialForAndroid/src/test/java/com/hoho/android/usbserial/driver/FtdiSerialDriverTest.java b/usbSerialForAndroid/src/test/java/com/hoho/android/usbserial/driver/FtdiSerialDriverTest.java
index eeda9dc..509ba76 100644
--- a/usbSerialForAndroid/src/test/java/com/hoho/android/usbserial/driver/FtdiSerialDriverTest.java
+++ b/usbSerialForAndroid/src/test/java/com/hoho/android/usbserial/driver/FtdiSerialDriverTest.java
@@ -48,7 +48,7 @@ public class FtdiSerialDriverTest {
         len = port.readFilter(buf, 0);
         assertEquals(len, 0);
 
-        assertThrows(IOException.class, () -> {port.readFilter(buf, 1);});
+        assertThrows(IOException.class, () -> port.readFilter(buf, 1));
 
         initBuf(buf);
         len = port.readFilter(buf, 2);
@@ -69,7 +69,7 @@ public class FtdiSerialDriverTest {
         assertEquals(len, 62);
         assertTrue(testBuf(buf, len));
 
-        assertThrows(IOException.class, () -> {port.readFilter(buf, 65);});
+        assertThrows(IOException.class, () -> port.readFilter(buf, 65));
 
         initBuf(buf);
         len = port.readFilter(buf, 66);