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