package headfirst.combining.observer;public class DuckCall implements Quackable {	Observable observable;	public DuckCall() {		observable = new Observable(this);	} 	public void quack() {		System.out.println("Kwak");		notifyObservers();	} 	public void registerObserver(Observer observer) {		observable.registerObserver(observer);	}	public void notifyObservers() {		observable.notifyObservers();	} 	public String toString() {		return "Duck Call";	}}