public interface MessageListener
{
  void receive (Message msg);

  // Group members can share state
  void getState (OutputStream output) throws Exception;
  void setState(InputStream input) throws Exception;
}

public interface MembershipListener
{
  // Notification about membership view change
  public void viewAccepted (View view);

  // Indication of suspect member before actual removal
  public void suspect (Object suspected);

  // Notifies about temporary suspension during view update
  public void block ();
  public void unblock ();
}

public interface Receiver extends MessageListener, MembershipListener;