Java回调函数与观察者模式实例代码

package com.demo.test;
import java.util.Observable;
import java.util.Observer;
//观察者模式里面目标类维护了所有观察者的引用，而回调里面只是维护了一个引用
public class ObserverCallbackDemo {
	// 观察者A
	static class ConcreteObserverA implements Observer {
		@Override
		    public void update(Observable o, Object arg) {
			System.out.println("ConcreteObserverA update");
		}
	}
	// 观察者B
	static class ConcreteObserverB implements Observer {
		@Override
		    public void update(Observable o, Object arg) {
			System.out.println("ConcreteObserverB update");
		}
	}
	// 被观察对象
	static class ConcreteObservable extends Observable {
		public void changeValue() {
			//protected方法只能在子类被调用
			setChanged();
			notifyObservers();
		}
	}
	// 回调函数接口
	interface ICallback {
		public void onCall();
	}
	// 回调类
	static class CallbackDemo {
		private ICallback callback;
		public void setListener(ICallback callback) {
			this.callback = callback;
		}
		public void call() {
			callback.onCall();
		}
	}
	public static void main(String[] args) {
		// 观察者
		ConcreteObserverA observerA = new ConcreteObserverA();
		ConcreteObserverB observerB = new ConcreteObserverB();
		ConcreteObservable observable = new ConcreteObservable();
		observable.addObserver(observerA);
		observable.addObserver(observerB);
		System.out.println("countObservers = " + observable.countObservers());
		observable.changeValue();
		// 回调函数
		CallbackDemo callbackDemo = new CallbackDemo();
		callbackDemo.setListener(new ICallback() {
			@Override
			      public void onCall() {
				System.out.println("callback onCall");
			}
		}
		);
		callbackDemo.call();
	}
}