观察者模式

public interface Subject {
    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers();
}public class LogitechSupplier implements Subject {
    Vector<Observer> observers;
    String message;
    public LogitechSupplier(){
        observers = new Vector<>();
    }
    @Override
    public void registerObserver(Observer observer) {
        observers.addElement(observer);
    }

    @Override
    public void removeObserver(Observer observer) {
        observers.removeElement(observer);
    }

    @Override
    public void notifyObservers() {
        for(Observer observer:observers){
            observer.update(message);
        }
    }
    public void messageChanged(String message){
        this.message=message;
        notifyObservers();
    }
}

public interface Observer {
    void update(Object args);
}

public class TBShop implements Observer {
    Subject subject;

    public TBShop(Subject subject) {
        this.subject = subject;
        subject.registerObserver(this);
    }

    @Override
    public void update(Object args) {
        System.out.println("天猫商城收到消息:"+args);
    }
}

public class JDShop implements Observer {
    Subject subject;//通过持有主题，可以从主题拉取数据
    public JDShop(Subject subject){
        this.subject=subject;
        subject.registerObserver(this);
    }
    @Override
    public void update(Object args) {
        System.out.println("京东商城收到消息:"+args);
    }
}

public class ObserverPatternTestDemo {
    public static void main(String args[]){
        //获取主题
        LogitechSupplier logitechSupplier = new LogitechSupplier();
        //观察者注册
        Observer jdShop = new JDShop(logitechSupplier);
        Observer tbShop = new TBShop(logitechSupplier);
        //主题向观察者推送消息
        logitechSupplier.messageChanged("新鼠标到货了!");
        logitechSupplier.messageChanged("机械键盘降价10%");
    }
}