xds: fix lint warnings (grpc#6869)

Author: zhangkun83

xds/src/main/java/io/grpc/xds/XdsClientWrapperForServerSds.java

@@ -67,7 +67,7 @@ public final class XdsClientWrapperForServerSds {
   private EnvoyServerProtoData.Listener curListener;
   // TODO(sanjaypujare): implement shutting down XdsServer which will need xdsClient reference
   @SuppressWarnings("unused")
-  @Nullable private XdsClient xdsClient;
+  @Nullable private final XdsClient xdsClient;
   private final int port;
   private final ScheduledExecutorService timeService;
 
@@ -158,7 +158,7 @@ public DownstreamTlsContext getDownstreamTlsContext(Channel channel) {
   }
 
   private static final class FilterChainComparator implements Comparator<FilterChain> {
-    private InetSocketAddress localAddress;
+    private final InetSocketAddress localAddress;
 
     private enum Match {
       NO_MATCH,

xds/src/test/java/io/grpc/xds/XdsClientWrapperForServerSdsTest.java

@@ -137,7 +137,7 @@ public static Iterable<Object[]> data() {
   @Mock private Channel channel;
 
   private XdsClientWrapperForServerSds xdsClientWrapperForServerSds;
-  private DownstreamTlsContext[] tlsContexts = new DownstreamTlsContext[3];
+  private final DownstreamTlsContext[] tlsContexts = new DownstreamTlsContext[3];
 
   @Before
   public void setUp() throws IOException {

xds/src/test/java/io/grpc/xds/XdsClientWrapperForServerSdsTestMisc.java

@@ -22,7 +22,6 @@
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
-import static org.mockito.internal.verification.VerificationModeFactory.times;
 
 import io.envoyproxy.envoy.api.v2.auth.DownstreamTlsContext;
 import io.grpc.inprocess.InProcessSocketAddress;
@@ -61,7 +60,7 @@ public void setUp() throws IOException {
 
   @Test
   public void verifyListenerWatcherRegistered() {
-    verify(xdsClient, times(1)).watchListenerData(eq(PORT), any(XdsClient.ListenerWatcher.class));
+    verify(xdsClient).watchListenerData(eq(PORT), any(XdsClient.ListenerWatcher.class));
   }
 
   @Test