Java观察者模式：实现松耦合的事件通知机制

import java.util.ArrayList;
import java.util.List;
// 主题接口
interface Subject {
    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers();
}
// 观察者接口
interface Observer {
    void update(String message);
}
// 具体主题
class ConcreteSubject implements Subject {
    private List<Observer> observers = new ArrayList<>();
    private String state;
    @Override
    public void registerObserver(Observer observer) {
        observers.add(observer);
    }
    @Override
    public void removeObserver(Observer observer) {
        observers.remove(observer);
    }
    @Override
    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update(state);
        }
    }
    public void setState(String state) {
        this.state = state;
        notifyObservers();
    }
}
// 具体观察者
class ConcreteObserver implements Observer {
    private String name;
    public ConcreteObserver(String name) {
        this.name = name;
    }
    @Override
    public void update(String message) {
        System.out.println(name + " received message: " + message);
    }
}

public class ObserverPatternExample {
    public static void main(String[] args) {
        ConcreteSubject subject = new ConcreteSubject();
        ConcreteObserver observer1 = new ConcreteObserver("Observer 1");
        ConcreteObserver observer2 = new ConcreteObserver("Observer 2");
        subject.registerObserver(observer1);
        subject.registerObserver(observer2);
        subject.setState("New state!");
    }
}

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
class MyModel {
    private String data;
    private PropertyChangeSupport support = new PropertyChangeSupport(this);
    public void addPropertyChangeListener(PropertyChangeListener listener) {
        support.addPropertyChangeListener(listener);
    }
    public void removePropertyChangeListener(PropertyChangeListener listener) {
        support.removePropertyChangeListener(listener);
    }
    public String getData() {
        return data;
    }
    public void setData(String newData) {
        String oldData = this.data;
        this.data = newData;
        support.firePropertyChange("data", oldData, newData);
    }
}
class MyListener implements PropertyChangeListener {
    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        System.out.println("Data changed: " + evt.getNewValue());
    }
}
public class ObserverPatternJavaAPIExample {
    public static void main(String[] args) {
        MyModel model = new MyModel();
        MyListener listener = new MyListener();
        model.addPropertyChangeListener(listener);
        model.setData("New data!");
    }
}