1. 类图
2. 角色
Subject:被观察者,抽象类ConcreteSubject:被观察者的具体类,每个具体类中有列表记录任意数量的观察者Observer:观察者接口ConcrereObserver:具体观察者3. 代码
观察者 观察者抽象接口public interface Observer {public void update(String message);}
观察者实现类
public class WeixinUser implements Observer {private String name; // 微信用户名public WeixinUser(String name) {this.name = name;}@Overridepublic void update(String message) {System.out.println(name + "-" + message);}}
被观察者 被观察者接口
public interface Subject {public void attach(Observer observer); //增加订阅者public void detach(Observer observer); //删除订阅者public void notify(String message); //通知订阅者更新消息}
被观察者实现类
public class SubscriptionSubject implements Subject {private List<Observer> weixinUserlist = new ArrayList<Observer>(); //储存订阅公众号的微信用户@Overridepublic void attach(Observer observer) {weixinUserlist.add(observer);}@Overridepublic void detach(Observer observer) {weixinUserlist.remove(observer);}@Overridepublic void notify(String message) {for (Observer observer : weixinUserlist) {observer.update(message);}}}
客户端调用
public class Client {public static void main(String[] args) {SubscriptionSubject mSubscriptionSubject=new SubscriptionSubject();//创建微信用户WeixinUser user1=new WeixinUser("杨影枫");WeixinUser user2=new WeixinUser("月眉儿");WeixinUser user3=new WeixinUser("紫轩");//订阅公众号mSubscriptionSubject.attach(user1);mSubscriptionSubject.attach(user2);mSubscriptionSubject.attach(user3);//公众号更新发出消息给订阅的微信用户mSubscriptionSubject.notify("刘望舒的专栏更新了");}}
4. 总结
优点:
解除耦合,让耦合的双方都依赖于抽象,从而使得各自的变换都不会影响另一边的变换
缺点:
开发效率和运行效率问题。一般采用异步实现