public interface Message ... {

    short BYTES_MSG   = 0,
        NIO_MSG       = 1,
        EMPTY_MSG     = 2,
        OBJ_MSG       = 3,
        LONG_MSG      = 4,
        COMPOSITE_MSG = 5,
        FRAG_MSG      = 6;

    short getType ();

    Address getDest ();
    Message setDest (Address new_dest);
    Address getSrc ();
    Message setSrc (Address new_src);

    // Headers are internal and interpreted by individual protocol modules
    Message putHeader (short id, Header hdr);
    <T extends Header> T getHeader (short id);
    Map<Short,Header> getHeaders ();

    // Flags are interpreted by individual protocol modules
    // Examples include disabling flow control or reliability
    short getFlags (boolean transient_flags);
    Message setFlag (short flag, boolean transient_flags);

    // Convenience methods on the interface
    // May not make sense for all message classes

    byte [] getArray ();
    int getOffset ();
    int getLength ();
    public Message setBuffer (byte [] b);
    Message setArray (byte [] b, int offset, int length);

    <T extends Object> T getObject ();
    Message setObject (Object obj);

    <T extends Object> T getPayload ();
    Message setPayload (Object pl);

    ...
}

public class BytesMessage ... {
    public BytesMessage (Address dest, byte [] array) { ... }
    public BytesMessage (Address dest, byte [] array, int offset, int length) { ... }
    ...
}

public class NioMessage ... {
    // Uses java.nio.ByteBuffer that can reduce copying overhead
    public NioMessage (Address dest, ByteBuffer buf) { ... }
    public ByteBuffer getBuf () { ... }
    public NioMessage setBuf (ByteBuffer b) { ... }
    ...
}

public class ObjectMessage ... {
    public ObjectMessage(Address dest, Object obj) {
    ...
}

public class CompositeMessage ... implements Iterable<Message> {
    public CompositeMessage (Address dest, Message ... messages) { ... }
    public CompositeMessage add (Message msg) { ... }
    public <T extends Message> T get (int index) { ... }
    public Iterator<Message> iterator () { ... }
    ...
}