public void addMessageObserver(final MessageObserver observer){
  if (observer == null) {
    throw new NullPointerException();
  }
 else   if (messageObservers == null) {
    initMessageObserverList();
  }
  messageObservers.add(observer);
}

public void addMessageObserver ( final MessageObserver observer ) { if ( observer == null ) { throw new NullPointerException ( ) ; } else if ( messageObservers == null ) { initMessageObserverList ( ) ; } messageObservers . add ( observer ) ; }
adds the specified message observer .
