观察者模式

          首先要说的是JDK已经帮我们定义好了观察者模式的接口，我们如果项目中需要使用观察者模式，只需简单继承一下就可以了。下面的一个例子是，出版社出版了一个杂志，要读者主动订阅。

 

Publisher.java

 

public class Publisher extends Observable{
	
	
	private String magazineName;
	public String getMagazineName() {
		return magazineName;
	}
	public void setMagazineName(String magazineName) {
		this.magazineName = magazineName;
	}
	public void publish (String magazineName){
		this.magazineName = magazineName;
		
		this.setChanged();
		this.notifyObservers(this);
		
	}

}

 

 Reader.java

 

public class Reader implements Observer {

	@Override
	public void update(Observable arg0, Object arg1) {
		
		if(arg0 instanceof Publisher){
			
			Publisher publisher = (Publisher)arg0;
			System.out.println("有新杂志。我要订阅"+publisher.getMagazineName());
		}
	}
	
}

 

 测试类：

 

public class TestCase {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		Publisher publisher  = new Publisher();
		
		Reader  zhangsan = new Reader();
		publisher.addObserver(zhangsan);
		
		Reader  lisi = new Reader();
		publisher.addObserver(lisi);
		
		publisher.publish("程序员第0321期");
		//结果
		//有新杂志。我要订阅 程序员第0321期
	}
}