package headfirst.combining.observer;import java.util.Iterator;import java.util.ArrayList;public class Observable implements QuackObservable {	ArrayList observers = new ArrayList();	QuackObservable duck; 	public Observable(QuackObservable duck) {		this.duck = duck;	}  	public void registerObserver(Observer observer) {		observers.add(observer);	}  	public void notifyObservers() {		Iterator iterator = observers.iterator();		while (iterator.hasNext()) {			Observer observer = (Observer)iterator.next();			observer.update(duck);		}	} 	public Iterator getObservers() {		return observers.iterator();	}}