MessageEvents not are used by the core VisAD classes. They are reserved for application-level events. They could be used by MessageEvents are sent by the Display's sendMessage(MessageEvent) method to listeners who have implemented the receiveMessage(MessageEvent) method and have registered themselves using the addMessageListener(MessageListener) method.

A trivial example of an application using MessageEvents looks like this:

import java.rmi.RemoteException;

import visad.java2d.DisplayImplJ2D;

import visad.MessageEvent;
import visad.VisADException;

public class SimpleMsgEvent
  implements visad.MessageListener
  private DisplayImplJ2D dpy;

  public SimpleMsgEvent()
    throws RemoteException, VisADException
    dpy = new DisplayImplJ2D("dpy");
    dpy.sendMessage(new MessageEvent(0));

  public void receiveMessage(MessageEvent evt)
    throws RemoteException
    final int id = evt.getId();


    if (id > 10) System.exit(0);

    dpy.sendMessage(new MessageEvent(id + 1));

  public static void main(String[] args)
    throws RemoteException, VisADException
    new SimpleMsgEvent();

A more complex example can be found in, which uses the MessageEvent ID to hold both a message type and a spreadsheet cell ID. It defines message types 0 through 8 to mean things like ADD_DATE, ADD_SOURCE, etc. and then computes the event ID by multiplying the cell ID by 9 and adding it to the message type. The receiving end can thus extract the cell ID with a simple event.getID() / 9 calculation. Similarly, the message type can be extracted with event.getID() % 9. The receiving cell can then ignore its own messages or those from cells it doesn't care about, only response to certain message types, etc.
Last modified: Thu Feb 14 09:20:20 CST 2002