Java and Implicit Invocation Java Event Model Illustration

Java and Implicit Invocation -Java Event Model - Illustration

Java Event Model add. Listener Event Source register event listener remove. Listener Event Object fire event. Handler Event Listener

Illustration: Event Object public class XEvent. Object extends Event. Object /* java. util. Event. Object */ { public XEvent. Object (Object o) /* o = event source object */ { super(o) /* invoke the constructor of the superclass, Event. Object */ … } } Public interface XListener extends Event. Listener /* java. util. Event. Listener */ { void handle. X (XEvent. Object xeo); } Interface attributes method 1 {} … Class X 1 Listener

Array: fixed size, homogeneous Vector: variable size, heterogeneous Illustration: Event Source public class XAnnouncer extends Canvas implements Runnable; { private Vector x. Listeners = new Vector; public XAnnouncer () { thread = new Thread(this) thread. start; } public synchronized void add. XListener (x. Listener l) /* only one thread inside this method at once */ {x. Listeners. add. Element(l); } public synchronized void remove. XListener(x. Listener l) {x. Listeners. remove. Element(l); } private void announce. X() {XEvent. Object xeo = new XEvent. Object(this); /* for each x. Listener member. Of x. Listeners, invoke event handler */ x. Listener. handle. X(xeo) } }

Illustration: Event Listener public class X 1 Listener extends Canvas implements XListener, Runnable; { public X 1 Listener (XAnnouncer x. Announcer) { x. Announcer. add. XListener(this) } public void handle. X (XEvent. Object xeo) {…} }