core: Hide RR's ReadyPicker and EmptyPicker

ReadyPicker hasn't been necessary since 111ff60e, when we stopped
calling super.pickSubchannel(). EmptyPicker was only used in tests, and
we can just compare the class name instead of doing an instanceof check.

Unfortunately, calling getClass() caused Java to start casting the
return value of pickerCaptor.getValue() based on its generics. Captors
don't verify the type they capture, so using any type other than
SubchannelPicker for the pickerCaptor is misleading and hides a cast.

core/src/main/java/io/grpc/util/RoundRobinLoadBalancer.java

@@ -284,7 +284,8 @@ public class RoundRobinLoadBalancer extends LoadBalancer {
     public abstract boolean isEquivalentTo(RoundRobinPicker picker);
   }
 
-  public static class ReadyPicker extends RoundRobinPicker {
+  @VisibleForTesting
+  static class ReadyPicker extends RoundRobinPicker {
     private static final AtomicIntegerFieldUpdater<ReadyPicker> indexUpdater =
         AtomicIntegerFieldUpdater.newUpdater(ReadyPicker.class, "index");
 
@@ -336,7 +337,8 @@ public class RoundRobinLoadBalancer extends LoadBalancer {
     }
   }
 
-  public static final class EmptyPicker extends RoundRobinPicker {
+  @VisibleForTesting
+  static final class EmptyPicker extends RoundRobinPicker {
 
     private final Status status;
 

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

@@ -232,13 +232,13 @@ final class WeightedRoundRobinLoadBalancer extends RoundRobinLoadBalancer {
   }
 
   @VisibleForTesting
-  final class WeightedRoundRobinPicker extends ReadyPicker {
+  final class WeightedRoundRobinPicker extends RoundRobinPicker {
     private final List<Subchannel> list;
     private final boolean enableOobLoadReport;
     private volatile EdfScheduler scheduler;
 
     WeightedRoundRobinPicker(List<Subchannel> list, boolean enableOobLoadReport) {
-      super(checkNotNull(list, "list"), random.nextInt(list.size()));
+      checkNotNull(list, "list");
       Preconditions.checkArgument(!list.isEmpty(), "empty list");
       this.list = list;
       this.enableOobLoadReport = enableOobLoadReport;

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

@@ -46,12 +46,12 @@ import io.grpc.LoadBalancer.Helper;
 import io.grpc.LoadBalancer.PickResult;
 import io.grpc.LoadBalancer.ResolvedAddresses;
 import io.grpc.LoadBalancer.Subchannel;
+import io.grpc.LoadBalancer.SubchannelPicker;
 import io.grpc.LoadBalancer.SubchannelStateListener;
 import io.grpc.SynchronizationContext;
 import io.grpc.internal.FakeClock;
 import io.grpc.services.InternalCallMetricRecorder;
 import io.grpc.services.MetricReport;
-import io.grpc.util.RoundRobinLoadBalancer.EmptyPicker;
 import io.grpc.xds.WeightedRoundRobinLoadBalancer.EdfScheduler;
 import io.grpc.xds.WeightedRoundRobinLoadBalancer.WeightedRoundRobinLoadBalancerConfig;
 import io.grpc.xds.WeightedRoundRobinLoadBalancer.WeightedRoundRobinPicker;
@@ -94,9 +94,9 @@ public class WeightedRoundRobinLoadBalancerTest {
   private LoadBalancer.PickSubchannelArgs mockArgs;
 
   @Captor
-  private ArgumentCaptor<WeightedRoundRobinPicker> pickerCaptor;
+  private ArgumentCaptor<SubchannelPicker> pickerCaptor;
   @Captor
-  private ArgumentCaptor<WeightedRoundRobinPicker> pickerCaptor2;
+  private ArgumentCaptor<SubchannelPicker> pickerCaptor2;
 
   private final List<EquivalentAddressGroup> servers = Lists.newArrayList();
 
@@ -200,8 +200,10 @@ public class WeightedRoundRobinLoadBalancerTest {
     verify(helper, times(2)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
     assertThat(pickerCaptor.getAllValues().size()).isEqualTo(2);
-    assertThat(pickerCaptor.getAllValues().get(0).getList().size()).isEqualTo(1);
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(0);
+    assertThat(weightedPicker.getList().size()).isEqualTo(1);
+    weightedPicker = (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     assertThat(weightedPicker.getList().size()).isEqualTo(2);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
@@ -245,7 +247,8 @@ public class WeightedRoundRobinLoadBalancerTest {
             .forNonError(ConnectivityState.READY));
     verify(helper, times(2)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
     weightedSubchannel1.onLoadReport(InternalCallMetricRecorder.createMetricReport(
@@ -266,7 +269,7 @@ public class WeightedRoundRobinLoadBalancerTest {
             .setAttributes(affinity).build()));
     verify(helper, times(3)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor2.capture());
-    weightedPicker = pickerCaptor2.getAllValues().get(2);
+    weightedPicker = (WeightedRoundRobinPicker) pickerCaptor2.getAllValues().get(2);
     pickResult = weightedPicker.pickSubchannel(mockArgs);
     assertThat(pickResult.getSubchannel()).isEqualTo(weightedSubchannel1);
     assertThat(pickResult.getStreamTracerFactory()).isNull();
@@ -299,7 +302,8 @@ public class WeightedRoundRobinLoadBalancerTest {
             .forNonError(ConnectivityState.READY));
     verify(helper, times(3)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(2);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(2);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
     WrrSubchannel weightedSubchannel3 = (WrrSubchannel) weightedPicker.getList().get(2);
@@ -364,7 +368,8 @@ public class WeightedRoundRobinLoadBalancerTest {
     verify(helper, times(3)).createSubchannel(
             any(CreateSubchannelArgs.class));
     verify(helper).updateBalancingState(eq(ConnectivityState.CONNECTING), pickerCaptor.capture());
-    assertThat(pickerCaptor.getValue()).isInstanceOf(EmptyPicker.class);
+    assertThat(pickerCaptor.getValue().getClass().getName())
+        .isEqualTo("io.grpc.util.RoundRobinLoadBalancer$EmptyPicker");
     assertThat(fakeClock.forwardTime(11, TimeUnit.SECONDS)).isEqualTo(1);
   }
 
@@ -386,7 +391,8 @@ public class WeightedRoundRobinLoadBalancerTest {
             .forNonError(ConnectivityState.READY));
     verify(helper, times(2)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
     weightedSubchannel1.onLoadReport(InternalCallMetricRecorder.createMetricReport(
@@ -440,8 +446,10 @@ public class WeightedRoundRobinLoadBalancerTest {
     verify(helper, times(2)).updateBalancingState(
         eq(ConnectivityState.READY), pickerCaptor.capture());
     assertThat(pickerCaptor.getAllValues().size()).isEqualTo(2);
-    assertThat(pickerCaptor.getAllValues().get(0).getList().size()).isEqualTo(1);
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(0);
+    assertThat(weightedPicker.getList().size()).isEqualTo(1);
+    weightedPicker = (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     assertThat(weightedPicker.getList().size()).isEqualTo(2);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
@@ -488,7 +496,8 @@ public class WeightedRoundRobinLoadBalancerTest {
             .forNonError(ConnectivityState.READY));
     verify(helper, times(2)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
     weightedSubchannel1.onLoadReport(InternalCallMetricRecorder.createMetricReport(
@@ -539,7 +548,8 @@ public class WeightedRoundRobinLoadBalancerTest {
         .forNonError(ConnectivityState.READY));
     verify(helper, times(2)).updateBalancingState(
         eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     assertThat(fakeClock.forwardTime(10, TimeUnit.SECONDS)).isEqualTo(1);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
@@ -598,7 +608,8 @@ public class WeightedRoundRobinLoadBalancerTest {
             .forNonError(ConnectivityState.READY));
     verify(helper, times(3)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(2);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(2);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
     WrrSubchannel weightedSubchannel3 = (WrrSubchannel) weightedPicker.getList().get(2);
@@ -640,7 +651,8 @@ public class WeightedRoundRobinLoadBalancerTest {
             .forNonError(ConnectivityState.READY));
     verify(helper, times(2)).updateBalancingState(
             eq(ConnectivityState.READY), pickerCaptor.capture());
-    WeightedRoundRobinPicker weightedPicker = pickerCaptor.getAllValues().get(1);
+    WeightedRoundRobinPicker weightedPicker =
+        (WeightedRoundRobinPicker) pickerCaptor.getAllValues().get(1);
     WrrSubchannel weightedSubchannel1 = (WrrSubchannel) weightedPicker.getList().get(0);
     WrrSubchannel weightedSubchannel2 = (WrrSubchannel) weightedPicker.getList().get(1);
     weightedSubchannel1.onLoadReport(InternalCallMetricRecorder.createMetricReport(