十四、行为型（观察者模式）
// 观察者接口
interface Observer {
void update(String message);
}
// 具体观察者A
class ConcreteObserverA implements Observer {
private String name;
public ConcreteObserverA(String name) {
this.name = name;
}
@Override
public void update(String message) {
System.out.println(name + " 收到通知: " + message);
}
}
// 具体观察者B
class ConcreteObserverB implements Observer {
private String name;
public ConcreteObserverB(String name) {
this.name = name;
}
@Override
public void update(String message) {
System.out.println(name + " 收到通知: " + message);
}
}
// 被观察者接口
interface Subject {
void registerObserver(Observer observer);
void removeObserver(Observer observer);
void notifyObservers(String message);
}
// 具体主题
class ConcreteSubject implements Subject {
private List<Observer> observers = new ArrayList<>();
@Override
public void registerObserver(Observer observer) {
observers.add(observer);
}
@Override
public void removeObserver(Observer observer) {
observers.remove(observer);
}
@Override
public void notifyObservers(String message) {
for (Observer observer : observers) {
observer.update(message);
}
}
}
// 客户端代码
public class ObserverPatternDemo {
public static void main(String[] args) {
ConcreteSubject subject = new ConcreteSubject();
Observer observer1 = new ConcreteObserverA("观察者1");
Observer observer2 = new ConcreteObserverB("观察者2");
subject.registerObserver(observer1);
subject.registerObserver(observer2);
// 通知所有观察者
subject.notifyObservers("主题状态发生变化");
// 移除观察者1，之后再次通知
subject.removeObserver(observer1);
subject.notifyObservers("第二次状态变化");
}
}