design_model（18）observe

最新推荐文章于 2025-05-11 11:23:08 发布

weixin_33894992

最新推荐文章于 2025-05-11 11:23:08 发布

阅读量89

点赞数

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/gg128/p/9571316.html

本文详细介绍了观察者模式的概念及其实现方式，通过两个具体的Java代码示例展示了如何使用观察者模式建立主题对象与多个观察者对象之间的依赖关系，并实现状态变化时的通知机制。

1.观察者模式

观察者模式定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象，这个主题对象在状态发生变化的时，会通知所有观察者对象，使他们能够自动更新自己。

2.实例1

public class ConcreteSubject implements Subject {
	private int i;

	public void setI(int i) {
		this.i = i;
	}

	private List<Observer> list = new ArrayList<>();

	public void add(Observer observer) {
		list.add(observer);
	}

	public void update() {
		for (Observer observer : list) {
			observer.update(i);
		}
	}
}

public class Observer {
	private int i;

	public void update(int i) {
		this.i = i;
	}

	public int getI() {
		return i;
	}
}

public interface Subject {
	
}

public class Client {
	public static void main(String[] args) {
		ConcreteSubject cs = new ConcreteSubject();
		cs.setI(3);
		Observer observer1 = new Observer();
		Observer observer2 = new Observer();
		cs.add(observer1);
		cs.add(observer2);
		cs.update();
		System.out.println(observer1.getI());
		System.out.println(observer1.getI());
	}
}

3.实例2

public class ConcreteSubject extends Observable {
	private int i;

	public void set(int s) {
		this.i = s;
		setChanged();
		notifyObservers(i);
	}

	public int getI() {
		return i;
	}

	public void setI(int i) {
		this.i = i;
	}

}

public class Observe implements Observer {

	private int i;

	@Override
	public void update(Observable o, Object arg) {
		this.i = ((ConcreteSubject) o).getI();
	}

	public int getI() {
		return i;
	}

	public void setI(int i) {
		this.i = i;
	}

}

public class Client {
	public static void main(String[] args) {
		ConcreteSubject cs = new ConcreteSubject();
		Observe observer1 = new Observe();
		Observe observer2 = new Observe();
		cs.addObserver(observer1);
		cs.addObserver(observer2);
		cs.set(3);
		System.out.println(observer1.getI());
		System.out.println(observer1.getI());
	}
}

//源码

public void notifyObservers(Object arg) {
        Object[] arrLocal;

        synchronized (this) {
            if (!changed)
                return;
            arrLocal = obs.toArray();
            clearChanged();
        }

        for (int i = arrLocal.length-1; i>=0; i--)
            ((Observer)arrLocal[i]).update(this, arg);
    }

转载于:https://www.cnblogs.com/gg128/p/9571316.html