[#1623] Fix javadocs for ChannelGroup

transport/src/main/java/io/netty/channel/group/ChannelGroup.java

@@ -25,6 +25,7 @@ import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.EventLoop;
 import io.netty.channel.ServerChannel;
 import io.netty.util.CharsetUtil;
+import io.netty.util.concurrent.GlobalEventExecutor;
 
 import java.util.Set;
 
@@ -42,7 +43,8 @@ import java.util.Set;
  * If you need to broadcast a message to more than one {@link Channel}, you can
  * add the {@link Channel}s associated with the recipients and call {@link ChannelGroup#write(Object)}:
  * <pre>
- * <strong>{@link ChannelGroup} recipients = new {@link DefaultChannelGroup}();</strong>
+ * <strong>{@link ChannelGroup} recipients =
+ *         new {@link DefaultChannelGroup}({@link GlobalEventExecutor}.INSTANCE);</strong>
  * recipients.add(channelA);
  * recipients.add(channelB);
  * ..
@@ -60,15 +62,17 @@ import java.util.Set;
  * This rule is very useful when you shut down a server in one shot:
  *
  * <pre>
- * <strong>{@link ChannelGroup} allChannels = new {@link DefaultChannelGroup}();</strong>
+ * <strong>{@link ChannelGroup} allChannels =
+ *         new {@link DefaultChannelGroup}({@link GlobalEventExecutor}.INSTANCE);</strong>
  *
  * public static void main(String[] args) throws Exception {
  *     {@link ServerBootstrap} b = new {@link ServerBootstrap}(..);
  *     ...
+ *     b.childHandler(new MyHandler());
  *
  *     // Start the server
  *     b.getPipeline().addLast("handler", new MyHandler());
- *     {@link Channel} serverChannel = b.bind(..);
+ *     {@link Channel} serverChannel = b.bind(..).sync();
  *     <strong>allChannels.add(serverChannel);</strong>
  *
  *     ... Wait until the shutdown signal reception ...
@@ -82,7 +86,7 @@ import java.util.Set;
  *     {@code @Override}
  *     public void channelActive({@link ChannelHandlerContext} ctx) {
  *         // closed on shutdown.
- *         <strong>allChannels.add(e.getChannel());</strong>
+ *         <strong>allChannels.add(ctx.channel());</strong>
  *         super.channelActive(ctx);
  *     }
  * }