bramble-android/src/main/java/org/briarproject/bramble/account/AndroidAccountManager.java

@@ -9,19 +9,22 @@ import org.briarproject.bramble.api.account.AccountManager;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
-import org.briarproject.bramble.util.IoUtils;
 
 import java.io.File;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.inject.Inject;
 
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
+
 class AndroidAccountManager extends AccountManagerImpl
 		implements AccountManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidAccountManager.class.getName());
+			getLogger(AndroidAccountManager.class.getName());
 
 	private static final String PREF_DB_KEY = "key";
 
@@ -37,7 +40,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		appContext = app.getApplicationContext();
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Override
 	@Nullable
 	protected String loadEncryptedDatabaseKey() {
@@ -47,7 +50,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		return key;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	private String getDatabaseKeyFromPreferences() {
 		String key = prefs.getString(PREF_DB_KEY, null);
@@ -56,7 +59,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		return key;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private void migrateDatabaseKeyToFile(String key) {
 		if (storeEncryptedDatabaseKey(key)) {
 			if (prefs.edit().remove(PREF_DB_KEY).commit())
@@ -81,7 +84,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		return PreferenceManager.getDefaultSharedPreferences(appContext);
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private void deleteAppData(SharedPreferences... clear) {
 		// Clear and commit shared preferences
 		for (SharedPreferences prefs : clear) {
@@ -97,7 +100,7 @@ class AndroidAccountManager extends AccountManagerImpl
 			for (File child : children) {
 				String name = child.getName();
 				if (!name.equals("lib") && !name.equals("shared_prefs")) {
-					IoUtils.deleteFileOrDir(child);
+					deleteFileOrDir(child);
 				}
 			}
 		}

bramble-android/src/main/java/org/briarproject/bramble/network/AndroidNetworkManager.java

@@ -13,8 +13,7 @@ import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.network.NetworkStatus;
 import org.briarproject.bramble.api.network.event.NetworkStatusEvent;
-import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
-import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.Scheduler;
 
 import java.util.concurrent.Future;
@@ -34,16 +33,17 @@ import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
 import static android.net.ConnectivityManager.TYPE_WIFI;
 import static android.os.Build.VERSION.SDK_INT;
 import static android.os.PowerManager.ACTION_DEVICE_IDLE_MODE_CHANGED;
+import static java.util.Objects.requireNonNull;
 import static java.util.concurrent.TimeUnit.MINUTES;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
-@MethodsNotNullByDefault
-@ParametersNotNullByDefault
+@NotNullByDefault
 class AndroidNetworkManager implements NetworkManager, Service {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidNetworkManager.class.getName());
+			getLogger(AndroidNetworkManager.class.getName());
 
 	// See android.net.wifi.WifiManager
 	private static final String WIFI_AP_STATE_CHANGED_ACTION =
@@ -56,6 +56,7 @@ class AndroidNetworkManager implements NetworkManager, Service {
 			new AtomicReference<>();
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
+	@Nullable
 	private volatile BroadcastReceiver networkStateReceiver = null;
 
 	@Inject
@@ -89,9 +90,8 @@ class AndroidNetworkManager implements NetworkManager, Service {
 
 	@Override
 	public NetworkStatus getNetworkStatus() {
-		ConnectivityManager cm = (ConnectivityManager)
-				appContext.getSystemService(CONNECTIVITY_SERVICE);
-		if (cm == null) throw new AssertionError();
+		ConnectivityManager cm = (ConnectivityManager) requireNonNull(
+				appContext.getSystemService(CONNECTIVITY_SERVICE));
 		NetworkInfo net = cm.getActiveNetworkInfo();
 		boolean connected = net != null && net.isConnected();
 		boolean wifi = connected && net.getType() == TYPE_WIFI;

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothPlugin.java

@@ -24,7 +24,6 @@ import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.BlockingQueue;
@@ -48,9 +47,11 @@ import static android.bluetooth.BluetoothAdapter.STATE_OFF;
 import static android.bluetooth.BluetoothAdapter.STATE_ON;
 import static android.bluetooth.BluetoothDevice.ACTION_FOUND;
 import static android.bluetooth.BluetoothDevice.EXTRA_DEVICE;
+import static java.util.Collections.shuffle;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 
 @MethodsNotNullByDefault
@@ -58,7 +59,7 @@ import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidBluetoothPlugin.class.getName());
+			getLogger(AndroidBluetoothPlugin.class.getName());
 
 	private static final int MAX_DISCOVERY_MS = 10_000;
 
@@ -259,7 +260,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 			appContext.unregisterReceiver(receiver);
 		}
 		// Shuffle the addresses so we don't always try the same one first
-		Collections.shuffle(addresses);
+		shuffle(addresses);
 		return addresses;
 	}
 

bramble-android/src/main/java/org/briarproject/bramble/plugin/tcp/AndroidLanTcpPlugin.java

@@ -32,17 +32,19 @@ import static android.net.ConnectivityManager.TYPE_WIFI;
 import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
+import static java.util.Objects.requireNonNull;
+import static java.util.logging.Logger.getLogger;
 
 @NotNullByDefault
 class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 
+	private static final Logger LOG =
+			getLogger(AndroidLanTcpPlugin.class.getName());
+
 	private static final byte[] WIFI_AP_ADDRESS_BYTES =
 			{(byte) 192, (byte) 168, 43, 1};
 	private static final InetAddress WIFI_AP_ADDRESS;
 
-	private static final Logger LOG =
-			Logger.getLogger(AndroidLanTcpPlugin.class.getName());
-
 	static {
 		try {
 			WIFI_AP_ADDRESS = InetAddress.getByAddress(WIFI_AP_ADDRESS_BYTES);
@@ -66,10 +68,8 @@ class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 		// Don't execute more than one connection status check at a time
 		connectionStatusExecutor =
 				new PoliteExecutor("AndroidLanTcpPlugin", ioExecutor, 1);
-		ConnectivityManager connectivityManager = (ConnectivityManager)
-				appContext.getSystemService(CONNECTIVITY_SERVICE);
-		if (connectivityManager == null) throw new AssertionError();
-		this.connectivityManager = connectivityManager;
+		connectivityManager = (ConnectivityManager) requireNonNull(
+				appContext.getSystemService(CONNECTIVITY_SERVICE));
 		wifiManager = (WifiManager) appContext.getApplicationContext()
 				.getSystemService(WIFI_SERVICE);
 		socketFactory = SocketFactory.getDefault();

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPlugin.java

@@ -8,8 +8,7 @@ import android.os.PowerManager;
 
 import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.network.NetworkManager;
-import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
-import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.system.Clock;
@@ -26,10 +25,10 @@ import javax.net.SocketFactory;
 import static android.content.Context.MODE_PRIVATE;
 import static android.content.Context.POWER_SERVICE;
 import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
+import static java.util.Objects.requireNonNull;
 import static java.util.concurrent.TimeUnit.MINUTES;
 
-@MethodsNotNullByDefault
-@ParametersNotNullByDefault
+@NotNullByDefault
 class AndroidTorPlugin extends TorPlugin {
 
 	// This tag may prevent Huawei's power manager from killing us
@@ -52,8 +51,7 @@ class AndroidTorPlugin extends TorPlugin {
 				appContext.getDir("tor", MODE_PRIVATE));
 		this.appContext = appContext;
 		PowerManager pm = (PowerManager)
-				appContext.getSystemService(POWER_SERVICE);
-		if (pm == null) throw new AssertionError();
+				requireNonNull(appContext.getSystemService(POWER_SERVICE));
 		wakeLock = new RenewableWakeLock(pm, scheduler, PARTIAL_WAKE_LOCK,
 				WAKE_LOCK_TAG, 1, MINUTES);
 	}

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPluginFactory.java

 package org.briarproject.bramble.plugin.tor;
 
 import android.content.Context;
-import android.os.Build;
 
 import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.event.EventBus;
@@ -26,12 +25,15 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.Immutable;
 import javax.net.SocketFactory;
 
+import static android.os.Build.VERSION.SDK_INT;
+import static java.util.logging.Logger.getLogger;
+
 @Immutable
 @NotNullByDefault
 public class AndroidTorPluginFactory implements DuplexPluginFactory {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidTorPluginFactory.class.getName());
+			getLogger(AndroidTorPluginFactory.class.getName());
 
 	private static final int MAX_LATENCY = 30 * 1000; // 30 seconds
 	private static final int MAX_IDLE_TIME = 30 * 1000; // 30 seconds
@@ -102,7 +104,7 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 			return null;
 		}
 		// Use position-independent executable for SDK >= 16
-		if (Build.VERSION.SDK_INT >= 16) architecture += "_pie";
+		if (SDK_INT >= 16) architecture += "_pie";
 
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidLocationUtils.java

@@ -15,12 +15,13 @@ import java.util.logging.Logger;
 import javax.inject.Inject;
 
 import static android.content.Context.TELEPHONY_SERVICE;
+import static java.util.logging.Logger.getLogger;
 
 @NotNullByDefault
 class AndroidLocationUtils implements LocationUtils {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidLocationUtils.class.getName());
+			getLogger(AndroidLocationUtils.class.getName());
 
 	private final Context appContext;
 
@@ -59,14 +60,14 @@ class AndroidLocationUtils implements LocationUtils {
 	}
 
 	private String getCountryFromPhoneNetwork() {
-		Object o = appContext.getSystemService(TELEPHONY_SERVICE);
-		TelephonyManager tm = (TelephonyManager) o;
-		return tm.getNetworkCountryIso();
+		TelephonyManager tm = (TelephonyManager)
+				appContext.getSystemService(TELEPHONY_SERVICE);
+		return tm == null ? "" : tm.getNetworkCountryIso();
 	}
 
 	private String getCountryFromSimCard() {
-		Object o = appContext.getSystemService(TELEPHONY_SERVICE);
-		TelephonyManager tm = (TelephonyManager) o;
-		return tm.getSimCountryIso();
+		TelephonyManager tm = (TelephonyManager)
+				appContext.getSystemService(TELEPHONY_SERVICE);
+		return tm == null ? "" : tm.getSimCountryIso();
 	}
 }

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidSecureRandomProvider.java

@@ -8,7 +8,6 @@ import android.content.ContentResolver;
 import android.content.Context;
 import android.net.wifi.WifiConfiguration;
 import android.net.wifi.WifiManager;
-import android.os.Build;
 import android.os.Parcel;
 import android.os.StrictMode;
 import android.provider.Settings;
@@ -23,6 +22,9 @@ import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static android.content.Context.WIFI_SERVICE;
+import static android.os.Build.FINGERPRINT;
+import static android.os.Build.SERIAL;
+import static android.os.Build.VERSION.SDK_INT;
 import static android.provider.Settings.Secure.ANDROID_ID;
 
 @Immutable
@@ -45,8 +47,8 @@ class AndroidSecureRandomProvider extends UnixSecureRandomProvider {
 		out.writeInt(android.os.Process.myPid());
 		out.writeInt(android.os.Process.myTid());
 		out.writeInt(android.os.Process.myUid());
-		if (Build.FINGERPRINT != null) out.writeUTF(Build.FINGERPRINT);
-		if (Build.SERIAL != null) out.writeUTF(Build.SERIAL);
+		if (FINGERPRINT != null) out.writeUTF(FINGERPRINT);
+		if (SERIAL != null) out.writeUTF(SERIAL);
 		ContentResolver contentResolver = appContext.getContentResolver();
 		String id = Settings.Secure.getString(contentResolver, ANDROID_ID);
 		if (id != null) out.writeUTF(id);
@@ -74,15 +76,13 @@ class AndroidSecureRandomProvider extends UnixSecureRandomProvider {
 		// Silence strict mode
 		StrictMode.ThreadPolicy tp = StrictMode.allowThreadDiskWrites();
 		super.writeSeed();
-		if (Build.VERSION.SDK_INT >= 16 && Build.VERSION.SDK_INT <= 18)
-			applyOpenSslFix();
+		if (SDK_INT >= 16 && SDK_INT <= 18) applyOpenSslFix();
 		StrictMode.setThreadPolicy(tp);
 	}
 
 	// Based on https://android-developers.googleblog.com/2013/08/some-securerandom-thoughts.html
 	private void applyOpenSslFix() {
-		byte[] seed = new UnixSecureRandomSpi().engineGenerateSeed(
-				SEED_LENGTH);
+		byte[] seed = new UnixSecureRandomSpi().engineGenerateSeed(SEED_LENGTH);
 		try {
 			// Seed the OpenSSL PRNG
 			Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto")

bramble-android/src/main/java/org/briarproject/bramble/util/AndroidUtils.java

@@ -3,17 +3,20 @@ package org.briarproject.bramble.util;
 import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothAdapter;
 import android.content.Context;
-import android.os.Build;
 import android.provider.Settings;
 
 import java.io.File;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
 
 import static android.content.Context.MODE_PRIVATE;
+import static android.os.Build.CPU_ABI;
+import static android.os.Build.CPU_ABI2;
+import static android.os.Build.SUPPORTED_ABIS;
 import static android.os.Build.VERSION.SDK_INT;
+import static java.util.Arrays.asList;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 public class AndroidUtils {
 
@@ -22,14 +25,13 @@ public class AndroidUtils {
 
 	private static final String STORED_REPORTS = "dev-reports";
 
-	@SuppressWarnings("deprecation")
 	public static Collection<String> getSupportedArchitectures() {
 		List<String> abis = new ArrayList<>();
 		if (SDK_INT >= 21) {
-			abis.addAll(Arrays.asList(Build.SUPPORTED_ABIS));
+			abis.addAll(asList(SUPPORTED_ABIS));
 		} else {
-			abis.add(Build.CPU_ABI);
-			if (Build.CPU_ABI2 != null) abis.add(Build.CPU_ABI2);
+			abis.add(CPU_ABI);
+			if (CPU_ABI2 != null) abis.add(CPU_ABI2);
 		}
 		return abis;
 	}
@@ -49,7 +51,7 @@ public class AndroidUtils {
 	}
 
 	private static boolean isValidBluetoothAddress(String address) {
-		return !StringUtils.isNullOrEmpty(address)
+		return !isNullOrEmpty(address)
 				&& BluetoothAdapter.checkBluetoothAddress(address)
 				&& !address.equals(FAKE_BLUETOOTH_ADDRESS);
 	}

bramble-android/src/main/java/org/briarproject/bramble/util/RenewableWakeLock.java

@@ -10,17 +10,19 @@ import java.util.concurrent.TimeUnit;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
 @ThreadSafe
 @NotNullByDefault
 public class RenewableWakeLock {
 
 	private static final Logger LOG =
-			Logger.getLogger(RenewableWakeLock.class.getName());
+			getLogger(RenewableWakeLock.class.getName());
 
 	/**
 	 * Automatically release the lock this many milliseconds after it's due
@@ -36,10 +38,12 @@ public class RenewableWakeLock {
 	private final Runnable renewTask;
 
 	private final Object lock = new Object();
+	@GuardedBy("lock")
 	@Nullable
-	private PowerManager.WakeLock wakeLock; // Locking: lock
+	private PowerManager.WakeLock wakeLock;
+	@GuardedBy("lock")
 	@Nullable
-	private ScheduledFuture future; // Locking: lock
+	private ScheduledFuture future;
 
 	public RenewableWakeLock(PowerManager powerManager,
 			ScheduledExecutorService scheduler, int levelAndFlags, String tag,

bramble-api/src/main/java/org/briarproject/bramble/api/Bytes.java

 package org.briarproject.bramble.api;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.util.Arrays;
 import java.util.Comparator;
 
 import javax.annotation.concurrent.ThreadSafe;
 
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
 /**
  * A wrapper around a byte array, to allow it to be stored in maps etc.
  */
@@ -56,8 +57,7 @@ public class Bytes implements Comparable<Bytes> {
 
 	@Override
 	public String toString() {
-		return getClass().getSimpleName() +
-				"(" + StringUtils.toHexString(getBytes()) + ")";
+		return getClass().getSimpleName() + "(" + toHexString(getBytes()) + ")";
 	}
 
 	public static class BytesComparator implements Comparator<Bytes> {

bramble-api/src/main/java/org/briarproject/bramble/api/Multiset.java

@@ -2,7 +2,6 @@ package org.briarproject.bramble.api;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.NoSuchElementException;
@@ -10,6 +9,8 @@ import java.util.Set;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Collections.unmodifiableSet;
+
 @NotThreadSafe
 @NotNullByDefault
 public class Multiset<T> {
@@ -96,6 +97,6 @@ public class Multiset<T> {
 	 * is unmodifiable.
 	 */
 	public Set<T> keySet() {
-		return Collections.unmodifiableSet(map.keySet());
+		return unmodifiableSet(map.keySet());
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/client/BdfMessageContext.java

@@ -5,10 +5,11 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageId;
 
 import java.util.Collection;
-import java.util.Collections;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.Collections.emptyList;
+
 @Immutable
 @NotNullByDefault
 public class BdfMessageContext {
@@ -23,7 +24,7 @@ public class BdfMessageContext {
 	}
 
 	public BdfMessageContext(BdfDictionary dictionary) {
-		this(dictionary, Collections.emptyList());
+		this(dictionary, emptyList());
 	}
 
 	public BdfDictionary getDictionary() {

bramble-api/src/main/java/org/briarproject/bramble/api/client/BdfMessageValidator.java

@@ -16,6 +16,7 @@ import java.util.logging.Logger;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_CLOCK_DIFFERENCE;
 
 @Immutable
@@ -23,7 +24,7 @@ import static org.briarproject.bramble.api.transport.TransportConstants.MAX_CLOC
 public abstract class BdfMessageValidator implements MessageValidator {
 
 	protected static final Logger LOG =
-			Logger.getLogger(BdfMessageValidator.class.getName());
+			getLogger(BdfMessageValidator.class.getName());
 
 	protected final ClientHelper clientHelper;
 	protected final MetadataEncoder metadataEncoder;

bramble-api/src/main/java/org/briarproject/bramble/api/data/BdfDictionary.java

@@ -4,7 +4,6 @@ import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.api.FormatException;
 
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.TreeMap;
 
 import javax.annotation.Nullable;
@@ -24,9 +23,9 @@ public class BdfDictionary extends TreeMap<String, Object> {
 	 * );
 	 * </pre>
 	 */
-	public static BdfDictionary of(Entry<String, ?>... entries) {
+	public static BdfDictionary of(BdfEntry... entries) {
 		BdfDictionary d = new BdfDictionary();
-		for (Entry<String, ?> e : entries) d.put(e.getKey(), e.getValue());
+		for (BdfEntry e : entries) d.put(e.getKey(), e.getValue());
 		return d;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/data/BdfList.java

@@ -4,12 +4,12 @@ import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.api.FormatException;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Arrays.asList;
 import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
 
 @NotThreadSafe
@@ -22,7 +22,7 @@ public class BdfList extends ArrayList<Object> {
 	 * </pre>
 	 */
 	public static BdfList of(Object... items) {
-		return new BdfList(Arrays.asList(items));
+		return new BdfList(asList(items));
 	}
 
 	public BdfList() {
@@ -33,6 +33,7 @@ public class BdfList extends ArrayList<Object> {
 		super(items);
 	}
 
+	@SuppressWarnings("BooleanMethodIsAlwaysInverted")
 	private boolean isInRange(int index) {
 		return index >= 0 && index < size();
 	}

bramble-api/src/main/java/org/briarproject/bramble/api/db/Transaction.java

@@ -3,11 +3,12 @@ package org.briarproject.bramble.api.db;
 import org.briarproject.bramble.api.event.Event;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Collections.emptyList;
+
 /**
  * A wrapper around a database transaction. Transactions are not thread-safe.
  */
@@ -53,7 +54,7 @@ public class Transaction {
 	 * Returns any events attached to the transaction.
 	 */
 	public List<Event> getEvents() {
-		if (events == null) return Collections.emptyList();
+		if (events == null) return emptyList();
 		return events;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/identity/Author.java

@@ -2,12 +2,12 @@ package org.briarproject.bramble.api.identity;
 
 import org.briarproject.bramble.api.Nameable;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 
 import javax.annotation.concurrent.Immutable;
 
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 /**
  * A pseudonym for a user.
@@ -28,7 +28,7 @@ public class Author implements Nameable {
 
 	public Author(AuthorId id, int formatVersion, String name,
 			byte[] publicKey) {
-		int nameLength = StringUtils.toUtf8(name).length;
+		int nameLength = toUtf8(name).length;
 		if (nameLength == 0 || nameLength > MAX_AUTHOR_NAME_LENGTH)
 			throw new IllegalArgumentException();
 		if (publicKey.length == 0 || publicKey.length > MAX_PUBLIC_KEY_LENGTH)

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/TransportId.java

 package org.briarproject.bramble.api.plugin;
 
-import org.briarproject.bramble.util.StringUtils;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 /**
  * Type-safe wrapper for a namespaced string that uniquely identifies a
@@ -11,12 +11,12 @@ public class TransportId {
 	/**
 	 * The maximum length of a transport identifier in UTF-8 bytes.
 	 */
-	public static int MAX_TRANSPORT_ID_LENGTH = 100;
+	public static final int MAX_TRANSPORT_ID_LENGTH = 100;
 
 	private final String id;
 
 	public TransportId(String id) {
-		int length = StringUtils.toUtf8(id).length;
+		int length = toUtf8(id).length;
 		if (length == 0 || length > MAX_TRANSPORT_ID_LENGTH)
 			throw new IllegalArgumentException();
 		this.id = id;

bramble-api/src/main/java/org/briarproject/bramble/api/sync/ClientId.java

 package org.briarproject.bramble.api.sync;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 
 import javax.annotation.concurrent.Immutable;
 
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
+
 /**
  * Type-safe wrapper for a namespaced string that uniquely identifies a sync
  * client.
@@ -16,12 +17,12 @@ public class ClientId implements Comparable<ClientId> {
 	/**
 	 * The maximum length of a client identifier in UTF-8 bytes.
 	 */
-	public static int MAX_CLIENT_ID_LENGTH = 100;
+	public static final int MAX_CLIENT_ID_LENGTH = 100;
 
 	private final String id;
 
 	public ClientId(String id) {
-		int length = StringUtils.toUtf8(id).length;
+		int length = toUtf8(id).length;
 		if (length == 0 || length > MAX_CLIENT_ID_LENGTH)
 			throw new IllegalArgumentException();
 		this.id = id;

bramble-api/src/main/java/org/briarproject/bramble/api/sync/MessageContext.java

@@ -4,10 +4,11 @@ import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.util.Collection;
-import java.util.Collections;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.Collections.emptyList;
+
 @Immutable
 @NotNullByDefault
 public class MessageContext {
@@ -22,7 +23,7 @@ public class MessageContext {
 	}
 
 	public MessageContext(Metadata metadata) {
-		this(metadata, Collections.emptyList());
+		this(metadata, emptyList());
 	}
 
 	public Metadata getMetadata() {

bramble-api/src/main/java/org/briarproject/bramble/util/IoUtils.java

@@ -16,12 +16,13 @@ import java.util.logging.Logger;
 import javax.annotation.Nullable;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
 public class IoUtils {
 
-	private static final Logger LOG = Logger.getLogger(IoUtils.class.getName());
+	private static final Logger LOG = getLogger(IoUtils.class.getName());
 
 	public static void deleteFileOrDir(File f) {
 		if (f.isFile()) {

bramble-api/src/main/java/org/briarproject/bramble/util/ValidationUtils.java

@@ -7,13 +7,15 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import javax.annotation.Nullable;
 
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
+
 @NotNullByDefault
 public class ValidationUtils {
 
 	public static void checkLength(@Nullable String s, int minLength,
 			int maxLength) throws FormatException {
 		if (s != null) {
-			int length = StringUtils.toUtf8(s).length;
+			int length = toUtf8(s).length;
 			if (length < minLength) throw new FormatException();
 			if (length > maxLength) throw new FormatException();
 		}
@@ -21,7 +23,7 @@ public class ValidationUtils {
 
 	public static void checkLength(@Nullable String s, int length)
 			throws FormatException {
-		if (s != null && StringUtils.toUtf8(s).length != length)
+		if (s != null && toUtf8(s).length != length)
 			throw new FormatException();
 	}
 

bramble-api/src/test/java/org/briarproject/bramble/api/data/BdfDictionaryTest.java

@@ -8,6 +8,7 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.Map.Entry;
 
+import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
@@ -19,15 +20,15 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	public void testConstructors() {
 		assertEquals(Collections.<String, Object>emptyMap(),
 				new BdfDictionary());
-		assertEquals(Collections.singletonMap("foo", NULL_VALUE),
-				new BdfDictionary(Collections.singletonMap("foo", NULL_VALUE)));
+		assertEquals(singletonMap("foo", NULL_VALUE),
+				new BdfDictionary(singletonMap("foo", NULL_VALUE)));
 	}
 
 	@Test
 	public void testFactoryMethod() {
 		assertEquals(Collections.<String, Object>emptyMap(),
 				BdfDictionary.of());
-		assertEquals(Collections.singletonMap("foo", NULL_VALUE),
+		assertEquals(singletonMap("foo", NULL_VALUE),
 				BdfDictionary.of(new BdfEntry("foo", NULL_VALUE)));
 	}
 
@@ -67,7 +68,7 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	}
 
 	@Test
-	public void testKeySetIteratorIsOrderedByKeys() throws Exception {
+	public void testKeySetIteratorIsOrderedByKeys() {
 		BdfDictionary d = new BdfDictionary();
 		d.put("a", 1);
 		d.put("d", 4);
@@ -86,7 +87,7 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	}
 
 	@Test
-	public void testValuesIteratorIsOrderedByKeys() throws Exception {
+	public void testValuesIteratorIsOrderedByKeys() {
 		BdfDictionary d = new BdfDictionary();
 		d.put("a", 1);
 		d.put("d", 4);
@@ -105,7 +106,7 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	}
 
 	@Test
-	public void testEntrySetIteratorIsOrderedByKeys() throws Exception {
+	public void testEntrySetIteratorIsOrderedByKeys() {
 		BdfDictionary d = new BdfDictionary();
 		d.put("a", 1);
 		d.put("d", 4);

bramble-api/src/test/java/org/briarproject/bramble/api/data/BdfListTest.java

@@ -5,26 +5,31 @@ import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.junit.Test;
 
-import java.util.Arrays;
-import java.util.Collections;
+import java.util.Random;
 
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyList;
 import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
+import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
+import static org.briarproject.bramble.util.StringUtils.getRandomString;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 
 public class BdfListTest extends BrambleTestCase {
 
+	private final Random random = new Random();
+
 	@Test
 	public void testConstructors() {
-		assertEquals(Collections.emptyList(), new BdfList());
-		assertEquals(Arrays.asList(1, 2, NULL_VALUE),
-				new BdfList(Arrays.asList(1, 2, NULL_VALUE)));
+		assertEquals(emptyList(), new BdfList());
+		assertEquals(asList(1, 2, NULL_VALUE),
+				new BdfList(asList(1, 2, NULL_VALUE)));
 	}
 
 	@Test
 	public void testFactoryMethod() {
-		assertEquals(Collections.emptyList(), BdfList.of());
-		assertEquals(Arrays.asList(1, 2, NULL_VALUE),
+		assertEquals(emptyList(), BdfList.of());
+		assertEquals(asList(1, 2, NULL_VALUE),
 				BdfList.of(1, 2, NULL_VALUE));
 	}
 
@@ -64,22 +69,21 @@ public class BdfListTest extends BrambleTestCase {
 	}
 
 	@Test
-	@SuppressWarnings("ConstantConditions")
-	public void testIndexOutOfBoundsReturnsDefaultValue() throws Exception {
+	public void testIndexOutOfBoundsReturnsDefaultValue() {
 		BdfList list = BdfList.of(1, 2, 3);
-		boolean defaultBoolean = true;
+		boolean defaultBoolean = random.nextBoolean();
 		assertEquals(defaultBoolean, list.getBoolean(-1, defaultBoolean));
 		assertEquals(defaultBoolean, list.getBoolean(3, defaultBoolean));
-		Long defaultLong = 123L;
+		Long defaultLong = random.nextLong();
 		assertEquals(defaultLong, list.getLong(-1, defaultLong));
 		assertEquals(defaultLong, list.getLong(3, defaultLong));
-		Double defaultDouble = 1.23;
+		Double defaultDouble = random.nextDouble();
 		assertEquals(defaultDouble, list.getDouble(-1, defaultDouble));
 		assertEquals(defaultDouble, list.getDouble(3, defaultDouble));
-		String defaultString = "123";
+		String defaultString = getRandomString(123);
 		assertEquals(defaultString, list.getString(-1, defaultString));
 		assertEquals(defaultString, list.getString(3, defaultString));
-		byte[] defaultBytes = new byte[] {1, 2, 3};
+		byte[] defaultBytes = getRandomBytes(123);
 		assertArrayEquals(defaultBytes, list.getRaw(-1, defaultBytes));
 		assertArrayEquals(defaultBytes, list.getRaw(3, defaultBytes));
 		BdfList defaultList = BdfList.of(1, 2, 3);
@@ -95,18 +99,17 @@ public class BdfListTest extends BrambleTestCase {
 	}
 
 	@Test
-	@SuppressWarnings("ConstantConditions")
-	public void testWrongTypeReturnsDefaultValue() throws Exception {
+	public void testWrongTypeReturnsDefaultValue() {
 		BdfList list = BdfList.of(1, 2, 3, true);
-		boolean defaultBoolean = true;
+		boolean defaultBoolean = random.nextBoolean();
 		assertEquals(defaultBoolean, list.getBoolean(0, defaultBoolean));
-		Long defaultLong = 123L;
+		Long defaultLong = random.nextLong();
 		assertEquals(defaultLong, list.getLong(3, defaultLong));
-		Double defaultDouble = 1.23;
+		Double defaultDouble = random.nextDouble();
 		assertEquals(defaultDouble, list.getDouble(0, defaultDouble));
-		String defaultString = "123";
+		String defaultString = getRandomString(123);
 		assertEquals(defaultString, list.getString(0, defaultString));
-		byte[] defaultBytes = new byte[] {1, 2, 3};
+		byte[] defaultBytes = getRandomBytes(123);
 		assertArrayEquals(defaultBytes, list.getRaw(0, defaultBytes));
 		BdfList defaultList = BdfList.of(1, 2, 3);
 		assertEquals(defaultList, list.getList(0, defaultList));

bramble-api/src/test/java/org/briarproject/bramble/test/TestUtils.java

@@ -12,12 +12,10 @@ import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.util.IoUtils;
 
 import java.io.File;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -25,6 +23,7 @@ import java.util.Random;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.util.Arrays.asList;
+import static java.util.Collections.sort;
 import static org.briarproject.bramble.api.identity.Author.FORMAT_VERSION;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
@@ -33,6 +32,7 @@ import static org.briarproject.bramble.api.properties.TransportPropertyConstants
 import static org.briarproject.bramble.api.sync.ClientId.MAX_CLIENT_ID_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_GROUP_DESCRIPTOR_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
 import static org.briarproject.bramble.util.StringUtils.getRandomString;
 
 public class TestUtils {
@@ -48,8 +48,10 @@ public class TestUtils {
 	}
 
 	public static void deleteTestDirectory(File testDir) {
-		IoUtils.deleteFileOrDir(testDir);
-		testDir.getParentFile().delete(); // Delete if empty
+		deleteFileOrDir(testDir);
+		// Delete parent directory only if it's empty
+		//noinspection ResultOfMethodCallIgnored
+		testDir.getParentFile().delete();
 	}
 
 	public static byte[] getRandomBytes(int length) {
@@ -145,7 +147,7 @@ public class TestUtils {
 		if (size == 0) throw new IllegalArgumentException();
 		List<Double> sorted = new ArrayList<>(size);
 		for (Number n : samples) sorted.add(n.doubleValue());
-		Collections.sort(sorted);
+		sort(sorted);
 		if (size % 2 == 1) return sorted.get(size / 2);
 		double low = sorted.get(size / 2 - 1), high = sorted.get(size / 2);
 		return (low + high) / 2;

bramble-core/src/main/java/org/briarproject/bramble/PoliteExecutor.java

@@ -10,6 +10,7 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.GuardedBy;
 
 import static java.util.logging.Level.FINE;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.now;
 
 /**
@@ -42,7 +43,7 @@ public class PoliteExecutor implements Executor {
 			int maxConcurrentTasks) {
 		this.delegate = delegate;
 		this.maxConcurrentTasks = maxConcurrentTasks;
-		log = Logger.getLogger(tag);
+		log = getLogger(tag);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/TimeLoggingExecutor.java

@@ -9,6 +9,7 @@ import java.util.concurrent.TimeUnit;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.FINE;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.now;
 
 @NotNullByDefault
@@ -22,7 +23,7 @@ public class TimeLoggingExecutor extends ThreadPoolExecutor {
 			RejectedExecutionHandler handler) {
 		super(corePoolSize, maxPoolSize, keepAliveTime, unit, workQueue,
 				handler);
-		log = Logger.getLogger(tag);
+		log = getLogger(tag);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/account/AccountManagerImpl.java

@@ -6,9 +6,7 @@ import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.identity.LocalAuthor;
-import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
-import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.util.IoUtils;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.BufferedReader;
 import java.io.File;
@@ -19,19 +17,21 @@ import java.io.InputStreamReader;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.StringUtils.fromHexString;
 import static org.briarproject.bramble.util.StringUtils.toHexString;
 
-@MethodsNotNullByDefault
-@ParametersNotNullByDefault
+@NotNullByDefault
 class AccountManagerImpl implements AccountManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(AccountManagerImpl.class.getName());
+			getLogger(AccountManagerImpl.class.getName());
 
 	private static final String DB_KEY_FILENAME = "db.key";
 	private static final String DB_KEY_BACKUP_FILENAME = "db.key.bak";
@@ -68,7 +68,7 @@ class AccountManagerImpl implements AccountManager {
 		return databaseKey;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	protected String loadEncryptedDatabaseKey() {
 		String key = readDbKeyFromFile(dbKeyFile);
@@ -83,7 +83,7 @@ class AccountManagerImpl implements AccountManager {
 		return key;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	private String readDbKeyFromFile(File f) {
 		if (!f.exists()) {
@@ -102,8 +102,8 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
-	protected boolean storeEncryptedDatabaseKey(String hex) {
+	@GuardedBy("stateChangeLock")
+	boolean storeEncryptedDatabaseKey(String hex) {
 		LOG.info("Storing database key in file");
 		// Create the directory if necessary
 		if (databaseConfig.getDatabaseKeyDirectory().mkdirs())
@@ -140,7 +140,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private void writeDbKeyToFile(String key, File f) throws IOException {
 		FileOutputStream out = new FileOutputStream(f);
 		out.write(key.getBytes("UTF-8"));
@@ -170,7 +170,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private boolean encryptAndStoreDatabaseKey(SecretKey key, String password) {
 		byte[] plaintext = key.getBytes();
 		byte[] ciphertext = crypto.encryptWithPassword(plaintext, password);
@@ -181,8 +181,8 @@ class AccountManagerImpl implements AccountManager {
 	public void deleteAccount() {
 		synchronized (stateChangeLock) {
 			LOG.info("Deleting account");
-			IoUtils.deleteFileOrDir(databaseConfig.getDatabaseKeyDirectory());
-			IoUtils.deleteFileOrDir(databaseConfig.getDatabaseDirectory());
+			deleteFileOrDir(databaseConfig.getDatabaseKeyDirectory());
+			deleteFileOrDir(databaseConfig.getDatabaseDirectory());
 			databaseKey = null;
 		}
 	}
@@ -197,7 +197,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable