Make ByteBuf an abstract class rather than an interface

- 5% improvement in throughput (HelloWorldServer example)
- Made CompositeByteBuf a concrete class (renamed from DefaultCompositeByteBuf) because there's no multiple inheritance in Java

Fixes #1536

buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java

@@ -32,7 +32,7 @@ import java.nio.charset.Charset;
 /**
  * A skeletal implementation of a buffer.
  */
-public abstract class AbstractByteBuf implements ByteBuf {
+public abstract class AbstractByteBuf extends ByteBuf {
 
     static final ResourceLeakDetector<ByteBuf> leakDetector = new ResourceLeakDetector<ByteBuf>(ByteBuf.class);
 

buffer/src/main/java/io/netty/buffer/AbstractByteBufAllocator.java

@@ -153,7 +153,7 @@ public abstract class AbstractByteBufAllocator implements ByteBufAllocator {
 
     @Override
     public CompositeByteBuf compositeHeapBuffer(int maxNumComponents) {
-        return new DefaultCompositeByteBuf(this, false, maxNumComponents);
+        return new CompositeByteBuf(this, false, maxNumComponents);
     }
 
     @Override
@@ -163,7 +163,7 @@ public abstract class AbstractByteBufAllocator implements ByteBufAllocator {
 
     @Override
     public CompositeByteBuf compositeDirectBuffer(int maxNumComponents) {
-        return new DefaultCompositeByteBuf(this, true, maxNumComponents);
+        return new CompositeByteBuf(this, true, maxNumComponents);
     }
 
     private static void validate(int initialCapacity, int maxCapacity) {

buffer/src/main/java/io/netty/buffer/EmptyByteBuf.java

@@ -31,7 +31,7 @@ import java.nio.charset.Charset;
 /**
  * An empty {@link ByteBuf} whose capacity and maximum capacity are all {@code 0}.
  */
-public final class EmptyByteBuf implements ByteBuf {
+public final class EmptyByteBuf extends ByteBuf {
 
     private static final ByteBuffer EMPTY_BYTE_BUFFER = ByteBuffer.allocateDirect(0);
     private static final long EMPTY_BYTE_BUFFER_ADDRESS;

buffer/src/main/java/io/netty/buffer/SwappedByteBuf.java

@@ -24,7 +24,7 @@ import java.nio.channels.GatheringByteChannel;
 import java.nio.channels.ScatteringByteChannel;
 import java.nio.charset.Charset;
 
-public final class SwappedByteBuf implements ByteBuf {
+public final class SwappedByteBuf extends ByteBuf {
 
     private final ByteBuf buf;
     private final ByteOrder order;

buffer/src/main/java/io/netty/buffer/Unpooled.java

@@ -274,7 +274,7 @@ public final class Unpooled {
             }
 
             if (!components.isEmpty()) {
-                return new DefaultCompositeByteBuf(ALLOC, false, maxNumComponents, components);
+                return new CompositeByteBuf(ALLOC, false, maxNumComponents, components);
             }
         }
 
@@ -298,7 +298,7 @@ public final class Unpooled {
         default:
             for (ByteBuf b: buffers) {
                 if (b.isReadable()) {
-                    return new DefaultCompositeByteBuf(ALLOC, false, maxNumComponents, buffers);
+                    return new CompositeByteBuf(ALLOC, false, maxNumComponents, buffers);
                 }
             }
         }
@@ -332,7 +332,7 @@ public final class Unpooled {
             }
 
             if (!components.isEmpty()) {
-                return new DefaultCompositeByteBuf(ALLOC, false, maxNumComponents, components);
+                return new CompositeByteBuf(ALLOC, false, maxNumComponents, components);
             }
         }
 
@@ -350,7 +350,7 @@ public final class Unpooled {
      * Returns a new big-endian composite buffer with no components.
      */
     public static CompositeByteBuf compositeBuffer(int maxNumComponents) {
-        return new DefaultCompositeByteBuf(ALLOC, false, maxNumComponents);
+        return new CompositeByteBuf(ALLOC, false, maxNumComponents);
     }
 
     /**

buffer/src/main/java/io/netty/buffer/UnreleasableByteBuf.java

@@ -30,7 +30,7 @@ import java.nio.charset.Charset;
  * A {@link ByteBuf} implementation that wraps another buffer to prevent a user from increasing or decreasing the
  * wrapped buffer's reference count.
  */
-final class UnreleasableByteBuf implements ByteBuf {
+final class UnreleasableByteBuf extends ByteBuf {
 
     private final ByteBuf buf;
     private SwappedByteBuf swappedBuf;

codec/src/main/java/io/netty/handler/codec/ReplayingDecoderBuffer.java

@@ -33,7 +33,7 @@ import java.nio.charset.Charset;
 /**
  * Special {@link ByteBuf} implementation which is used by the {@link ReplayingDecoder}
  */
-final class ReplayingDecoderBuffer implements ByteBuf {
+final class ReplayingDecoderBuffer extends ByteBuf {
 
     private static final Signal REPLAY = ReplayingDecoder.REPLAY;