Java The Complete Reference, Seventh Edition

import java.util.*;

// This is the observing class.

class Watcher implements Observer {

public void update(Observable obj, Object arg) {

System.out.println("update() called, count is " +

((Integer)arg).intValue());

}

}

/ This is the class being observed.

class BeingWatched extends Observable {

void counter(int period) {

for( ; period >=0; period--) {

setChanged();

notifyObservers(new Integer(period));

try {

Thread.sleep(100);

} catch(InterruptedException e) {

System.out.println("Sleep interrupted");

}

}

}

}

class ObserverDemo {

public static void main(String args[]) {

BeingWatched observed = new BeingWatched();

Watcher observing = new Watcher();

/* Add the observing to the list of observers for

observed object. */

observed.addObserver(observing);

observed.counter(10);

}

}

The output from this program is shown here:

update() called, count is 10

update() called, count is 9

update() called, count is 8

update() called, count is 7

update() called, count is 6

update() called, count is 5

update() called, count is 4

update() called, count is 3

update() called, count is 2

update() called, count is 1

update() called, count is 0

520 Part II: The Java Library