Java and Implicit Invocation

1. Java and Implicit Invocation Java Event Model Illustration

2. Java Event Model addListener Event Source register event listener removeListener Event Object Event Listener fire event eventHandler

3. Illustration: Event Object public class XEventObject extends EventObject /* java.util.EventObject */ { public XEventObject (Object o) /* o = event source object */ { super(o) /* invoke the constructor of the superclass, EventObject */ … } } Public interface XListener extends EventListener /* java.util.EventListener */ { void handleX (XEventObject xeo); }

4. Illustration: Event Source public class XAnnouncer extends Canvas implements Runnable; { private Vector xListeners = new Vector; public XAnnouncer () { thread = new Thread(this) thread.start; } public synchronized void addXListener (xListener l) /* only one thread inside this method at once */ {xListeners.addElement(l);} public synchronized void removeXListener(xListener l) {xListeners.removeElement(l);} private void announceX() {XEventObject xeo = new XEventObject(this); /* for each xListener memberOf xListeners, invoke event handler */ xListener.handleX(xeo) } }

5. Illustration: Event Listener public class X1Listener extends Canvas implements XListener, Runnable; { public X1Listener (XAnnouncer xAnnouncer) { xAnnouncer.addXListener(this) } public void handleX (XEventObject xeo) { … } }