Message Transfer Between Panels

Question

Hi all:
Here (http://www.erc.msstate.edu/~shravan/Hierarchy_files/slide0001.htm) is the hierarchy of the Java Swing application i want to develop. I have a "MainFrame" which has three panels (A, B and C). Those panels have sub panels ((A1, A2) (B1, B2) (C1, C2)). I have objects (which i am actually planning to implement as independent pluggable components using the "Observer" pattern) on these sub panels.
Now let us say an event happens on "Obj O1" (changes state) and this should trigger a change on "Obj O10" and "Obj O12". What is the best way to implement this? I mean .. how can we transfer a message from an object somewhere in the tree to another object somewhere else in the tree? Because i am implementing object O1 as pluggable component (using Observer pattern), i can add O10 and O12 as listeners (Observers) to it. But, how can i get the reference of O10 and O12 in the panel A1?
Could anyone please advice?
Thanks a lot in advance,
Shravan

Answer 1

Hi. I had to implement something similar to this, except my objects weren't all in the same container. What I did was create an EventManager that could register listeners of type EventListener. The EventListener interface had methods like onXXX(). When one object needed to communicate a message, it would tell the EventManager and all the listeners would be notified. Here is some pseudo/sample code:
public class EventManager
    private static List listeners = new ArrayList();
    public static void register(EventListener listener)
        listeners.add(listener);
    public static void unregister(EventListener listener)
        listeners.remove(listener);
    public static windowOpened(String name)
        for (int i = 0; i < listeners.size(); i++)
            ((EventListener)listeners.get(i)).onWindowOpen(name);
public interface EventListener
    public void onWindowOpen(String name);
public class SomeClass
    public void doSomething()
        EventManager.windowOpened("bob");
public class SomeOtherClass implements EventListener
    public void onWindowOpen(String name)
}