public void addMessageListener( MessageListener<? super S> listener, Class... classes )
    {
        if( listener == null )
            throw new IllegalArgumentException( "Listener cannot be null." );
        for( Class c : classes ) {
            getListeners(c, true).add(listener);
        }
    }
Keeps track of message listeners registered to specific
 types or to any type.

 @version   $Revision$
 @author    Paul Speed
jme3-networking/src/main/java/com/jme3/network/base/MessageListenerRegistry.java