Q：观察者模式属于哪一类设计模式

A：观察者模式属于行为学模式

Q：什么是观察者模式

A：当一个对象的状态发生改变时，所有依赖它的对象都得到通知，并自动更新

观察者模式解析：报纸类维护了一个订阅者数组，我们可以通过报纸类遍历订阅者数组来通知所有订阅者

订阅者类

public interface Subscriber { void update(String message); }

订阅者实现类

public class SubscriberImpl implements Subscriber {private String name;@Overridepublic void update(String message) {System.out.println(name + "---接收到消息:" + message);}
}

报纸类

public interface NewsPaper {void addSubscriber(Subscriber subscriber);//添加订阅者void removeSubscriber(Subscriber subscriber);//移除订阅者void notifySubscriber(String message);//通知订阅者
}

报纸实现类

public class NewsPaperImpl implements NewsPaper {private List<Subscriber> subscribers = new ArrayList<>();@Overridepublic void addSubscriber(Subscriber subscriber) { subscribers.add(subscriber); }@Overridepublic void removeSubscriber(Subscriber subscriber) { subscribers.remove(subscriber); }@Overridepublic void notifySubscriber(String message) {for (Subscriber s : subscribers) {s.update(message);}}
}

演示类

public class Demo {public static void main(String[] args) {NewsPaperImpl newsPaper = new NewsPaperImpl();SubscriberImpl subscriber1 = new SubscriberImpl("李老头");SubscriberImpl subscriber2 = new SubscriberImpl("王奶奶");newsPaper.addSubscriber(subscriber1);newsPaper.addSubscriber(subscriber2);newsPaper.notifySubscriber("今天的报纸收到了！");newsPaper.removeSubscriber(subscriber1);newsPaper.notifySubscriber("明天的报纸还是这个点到！");}
}

演示结果