Make it possible to use MessageNano.mergeFrom without casting.

You can now do:

  MyMessage foo = MessageNano.mergeFrom(new MyMessage(), bytes);

without having to cast the message returned from mergeFrom.

Change-Id: Ibb2ad327f75855d45352ad304c7f054f20dd29c9

2 files changed, 12 insertions, 3 deletions

diff --git a/java/src/main/java/com/google/protobuf/nano/MessageNano.java b/java/src/main/java/com/google/protobuf/nano/MessageNano.java
index 5c1eb2ff..8d4ec39e 100644
--- a/java/src/main/java/com/google/protobuf/nano/MessageNano.java
+++ b/java/src/main/java/com/google/protobuf/nano/MessageNano.java
@@ -101,7 +101,7 @@ public abstract class MessageNano {
      * Parse {@code data} as a message of this type and merge it with the
      * message being built.
      */
-    public static final MessageNano mergeFrom(MessageNano msg, final byte[] data)
+    public static final <T extends MessageNano> T mergeFrom(T msg, final byte[] data)
         throws InvalidProtocolBufferNanoException {
         return mergeFrom(msg, data, 0, data.length);
     }
@@ -110,8 +110,8 @@ public abstract class MessageNano {
      * Parse {@code data} as a message of this type and merge it with the
      * message being built.
      */
-    public static final MessageNano mergeFrom(MessageNano msg, final byte[] data, final int off,
-        final int len) throws InvalidProtocolBufferNanoException {
+    public static final <T extends MessageNano> T mergeFrom(T msg, final byte[] data,
+            final int off, final int len) throws InvalidProtocolBufferNanoException {
         try {
             final CodedInputByteBufferNano input =
                 CodedInputByteBufferNano.newInstance(data, off, len);
diff --git a/java/src/test/java/com/google/protobuf/NanoTest.java b/java/src/test/java/com/google/protobuf/NanoTest.java
index 38fafb9e..19f39575 100644
--- a/java/src/test/java/com/google/protobuf/NanoTest.java
+++ b/java/src/test/java/com/google/protobuf/NanoTest.java
@@ -2241,6 +2241,15 @@ public class NanoTest extends TestCase {
     assertEquals(0, MessageNano.toByteArray(deserialized).length);
   }
 
+  public void testMergeFrom() throws Exception {
+    SimpleMessageNano message = new SimpleMessageNano();
+    message.d = 123;
+    byte[] bytes = MessageNano.toByteArray(message);
+
+    SimpleMessageNano newMessage = MessageNano.mergeFrom(new SimpleMessageNano(), bytes);
+    assertEquals(message.d, newMessage.d);
+  }
+
   private <T> List<T> list(T first, T... remaining) {
     List<T> list = new ArrayList<T>();
     list.add(first);