Addressed comments

Author: sakthivelmanii

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncResultSetImpl.java

@@ -615,7 +615,7 @@ public ResultSetMetadata getMetadata() {
     return delegateResultSet.get().getMetadata();
   }
 
-  public boolean initiateStreaming(StreamMessageListener streamMessageListener) {
+  boolean initiateStreaming(StreamMessageListener streamMessageListener) {
     return StreamingUtil.initiateStreaming(delegateResultSet.get(), streamMessageListener);
   }
 

google-cloud-spanner/src/main/java/com/google/cloud/spanner/ForwardingResultSet.java

@@ -16,6 +16,7 @@
 
 package com.google.cloud.spanner;
 
+import com.google.api.core.InternalApi;
 import com.google.common.base.Preconditions;
 import com.google.common.base.Supplier;
 import com.google.common.base.Suppliers;
@@ -105,6 +106,7 @@ public ResultSetMetadata getMetadata() {
   }
 
   @Override
+  @InternalApi
   public boolean initiateStreaming(AsyncResultSet.StreamMessageListener streamMessageListener) {
     return StreamingUtil.initiateStreaming(delegate.get(), streamMessageListener);
   }

google-cloud-spanner/src/main/java/com/google/cloud/spanner/GrpcResultSet.java

@@ -19,6 +19,7 @@
 import static com.google.cloud.spanner.SpannerExceptionFactory.newSpannerException;
 import static com.google.common.base.Preconditions.checkState;
 
+import com.google.api.core.InternalApi;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.protobuf.Value;
 import com.google.spanner.v1.PartialResultSet;
@@ -125,6 +126,7 @@ public ResultSetMetadata getMetadata() {
   }
 
   @Override
+  @InternalApi
   public boolean initiateStreaming(AsyncResultSet.StreamMessageListener streamMessageListener) {
     return iterator.initiateStreaming(streamMessageListener);
   }

google-cloud-spanner/src/main/java/com/google/cloud/spanner/GrpcStreamIterator.java

@@ -20,6 +20,7 @@
 import com.google.cloud.spanner.AbstractResultSet.CloseableIterator;
 import com.google.cloud.spanner.spi.v1.SpannerRpc;
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
 import com.google.common.collect.AbstractIterator;
 import com.google.common.util.concurrent.Uninterruptibles;
 import com.google.spanner.v1.PartialResultSet;
@@ -68,8 +69,8 @@ protected final SpannerRpc.ResultStreamConsumer consumer() {
     return consumer;
   }
 
-  public void registerListener(AsyncResultSet.StreamMessageListener streamMessageListener) {
-    this.streamMessageListener = streamMessageListener;
+  void registerListener(AsyncResultSet.StreamMessageListener streamMessageListener) {
+    this.streamMessageListener = Preconditions.checkNotNull(streamMessageListener);
   }
 
   public void setCall(SpannerRpc.StreamingCall call, boolean withBeginTransaction) {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/ResumableStreamIterator.java

@@ -23,6 +23,7 @@
 
 import com.google.api.client.util.BackOff;
 import com.google.api.client.util.ExponentialBackOff;
+import com.google.api.core.InternalApi;
 import com.google.api.gax.grpc.GrpcStatusCode;
 import com.google.api.gax.retrying.RetrySettings;
 import com.google.api.gax.rpc.StatusCode.Code;
@@ -223,6 +224,7 @@ public boolean isWithBeginTransaction() {
   }
 
   @Override
+  @InternalApi
   public boolean initiateStreaming(AsyncResultSet.StreamMessageListener streamMessageListener) {
     this.streamMessageListener = streamMessageListener;
     startGrpcStreaming();

google-cloud-spanner/src/main/java/com/google/cloud/spanner/StreamingResultSet.java

@@ -16,12 +16,16 @@
 
 package com.google.cloud.spanner;
 
+import com.google.api.core.InternalApi;
+
 /** Streaming implementation of ResultSet that supports streaming of chunks */
 interface StreamingResultSet extends ResultSet {
 
   /**
    * Returns the {@link boolean} for this {@link ResultSet}. This method will be used by
-   * AsyncResultSet to initiate gRPC streaming
+   * AsyncResultSet internally to initiate gRPC streaming. This method should not be called by the
+   * users.
    */
+  @InternalApi
   boolean initiateStreaming(AsyncResultSet.StreamMessageListener streamMessageListener);
 }

google-cloud-spanner/src/main/java/com/google/cloud/spanner/StreamingUtil.java

@@ -16,7 +16,10 @@
 
 package com.google.cloud.spanner;
 
-class StreamingUtil {
+final class StreamingUtil {
+
+  private StreamingUtil() {}
+
   static boolean initiateStreaming(
       ResultSet resultSet, AsyncResultSet.StreamMessageListener streamMessageListener) {
     if (resultSet instanceof StreamingResultSet) {