观察者模式

// Observer接口
public interface Observer {
    void update(String stockName, double stockPrice);
}

// Subject接口
public interface Subject {
    void attach(Observer o);
    void detach(Observer o);
    void notifyObservers();
}

// ConcreteSubject类
import java.util.ArrayList;
import java.util.List;

public class Stock implements Subject {
    private String name;
    private double price;
    private List<Observer> observers = new ArrayList<>();

    public Stock(String name, double price){
        this.name = name;
        this.price = price;
    }

    public void setPrice(double price){
        this.price = price;
        System.out.println(name + " 的价格已更新为: " + this.price);
        notifyObservers();
    }

    public double getPrice(){
        return this.price;
    }

    public String getName(){
        return this.name;
    }

    @Override
    public void attach(Observer o){
        observers.add(o);
    }

    @Override
    public void detach(Observer o){
        observers.remove(o);
    }

    @Override
    public void notifyObservers(){
        for(Observer o : observers){
            o.update(this.name, this.price);
        }
    }
}

// ConcreteObserver类
public class Investor implements Observer {
    private String name;

    public Investor(String name){
        this.name = name;
    }

    @Override
    public void update(String stockName, double stockPrice){
        System.out.println("投资者 " + name + " 收到通知: " + stockName + " 的最新价格为 " + stockPrice);
    }
}

// 客户端代码
public class ObserverPatternDemo {
    public static void main(String[] args) {
        Stock apple = new Stock("Apple", 150.00);
        Investor investor1 = new Investor("Tom");
        Investor investor2 = new Investor("Jerry");

        apple.attach(investor1);
        apple.attach(investor2);

        apple.setPrice(155.00);
        apple.setPrice(160.50);

        apple.detach(investor1);

        apple.setPrice(165.75);
    }
}

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;

// Observer接口
interface ButtonClickObserver {
    void onButtonClick(String message);
}

// Subject类
class ButtonSubject {
    private List<ButtonClickObserver> observers = new ArrayList<>();

    public void attach(ButtonClickObserver observer){
        observers.add(observer);
    }

    public void detach(ButtonClickObserver observer){
        observers.remove(observer);
    }

    public void notifyObservers(String message){
        for(ButtonClickObserver observer : observers){
            observer.onButtonClick(message);
        }
    }

    public void clickButton(){
        // 模拟按钮点击事件
        notifyObservers("按钮被点击了！");
    }
}

// ConcreteObserver类
class LabelUpdater implements ButtonClickObserver {
    private JLabel label;

    public LabelUpdater(JLabel label){
        this.label = label;
    }

    @Override
    public void onButtonClick(String message){
        label.setText(message);
    }
}

// 客户端代码
public class ObserverPatternGUI {
    public static void main(String[] args) {
        JFrame frame = new JFrame("观察者模式示例");
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JButton button = new JButton("点击我");
        JLabel label = new JLabel("按钮未被点击");
        frame.setLayout(null);

        button.setBounds(100, 50, 100, 30);
        label.setBounds(100, 100, 200, 30);

        frame.add(button);
        frame.add(label);

        // 创建被观察者和观察者
        ButtonSubject buttonSubject = new ButtonSubject();
        LabelUpdater labelUpdater = new LabelUpdater(label);
        buttonSubject.attach(labelUpdater);

        // 添加按钮点击事件监听
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                buttonSubject.clickButton();
            }
        });

        frame.setVisible(true);
    }
}

// Observer接口
public interface Follower {
    void update(String userName, String content);
}

// Subject接口
public interface User {
    void follow(Follower follower);
    void unfollow(Follower follower);
    void notifyFollowers();
    void postContent(String content);
    String getName();
    String getContent();
}

// ConcreteSubject类
import java.util.ArrayList;
import java.util.List;

public class ConcreteUser implements User {
    private String name;
    private String content;
    private List<Follower> followers = new ArrayList<>();

    public ConcreteUser(String name){
        this.name = name;
    }

    @Override
    public void follow(Follower follower){
        followers.add(follower);
    }

    @Override
    public void unfollow(Follower follower){
        followers.remove(follower);
    }

    @Override
    public void notifyFollowers(){
        for(Follower follower : followers){
            follower.update(this.name, this.content);
        }
    }

    @Override
    public void postContent(String content){
        this.content = content;
        System.out.println(this.name + " 发布新内容: " + this.content);
        notifyFollowers();
    }

    @Override
    public String getName(){
        return this.name;
    }

    @Override
    public String getContent(){
        return this.content;
    }
}

// ConcreteObserver类
public class UserFollower implements Follower {
    private String followerName;

    public UserFollower(String followerName){
        this.followerName = followerName;
    }

    @Override
    public void update(String userName, String content){
        System.out.println("关注者 " + followerName + " 收到通知: " + userName + " 发布了新内容 - " + content);
    }
}

// 客户端代码
public class ObserverPatternSocialMediaDemo {
    public static void main(String[] args) {
        User alice = new ConcreteUser("Alice");
        User bob = new ConcreteUser("Bob");

        Follower follower1 = new UserFollower("Tom");
        Follower follower2 = new UserFollower("Jerry");
        Follower follower3 = new UserFollower("Lily");

        alice.follow(follower1);
        alice.follow(follower2);
        bob.follow(follower3);

        alice.postContent("Hello, this is Alice!");
        bob.postContent("Bob's first post.");
        alice.postContent("Alice's second post.");
    }
}