观察者模式在Java接口中的应用解析

// 观察者接口
interface Observer {
    void update(String message);
}

// 被观察者接口
interface Subject {
    void registerObserver(Observer o);
    void removeObserver(Observer o);
    void notifyObservers();
}

import java.util.ArrayList;
import java.util.List;

class NewsAgency implements Subject {
    private List<Observer> observers = new ArrayList<>();
    private String news;

    public void setNews(String news) {
        this.news = news;
        notifyObservers(); // 状态变更后通知
    }

    public void registerObserver(Observer o) {
        observers.add(o);
    }

    public void removeObserver(Observer o) {
        observers.remove(o);
    }

    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update(news);
        }
    }
}

class NewsChannel implements Observer {
    private String news;

    public void update(String news) {
        this.news = news;
        display();
    }

    private void display() {
        System.out.println("NewsChannel received: " + news);
    }
}

NewsAgency agency = new NewsAgency();
NewsChannel channel1 = new NewsChannel();
NewsChannel channel2 = new NewsChannel();

agency.registerObserver(channel1);
agency.registerObserver(channel2);

agency.setNews("Breaking: Java 21 released!");
// 输出两条消息