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第一篇博客

admin 11月 13, 2020 0

观察者模式

观察者定义了一种一对多的依赖关系，多个观察者监听一个主题对象，当主题对象的状态发生改变时，这些观察者会被通知从而自我跟新。

结构图

具体代码如下

abstract class Subject{

    private ArrayList<BaseObserver> list=new ArrayList<>();

    public void attach(BaseObserver observer){
        list.add(observer);
    }

    public void Deattach(Observer observer){
        list.remove(observer);
    }

    public void notifyall(){
        for(BaseObserver observer:list){
            observer.update();
        }
    }

}

class ConcreteSubject extends Subject{

    private int state;

    public int getState() {
        return state;
    }

    public void setState(int state) {
        this.state = state;
    }
}

abstract class BaseObserver {
    protected Subject subject;
    public abstract void update();
}

class BinaryObserver extends BaseObserver{

    public BinaryObserver(Subject subject){
        this.subject=subject;
    }


    @Override
    public void update() {
        System.out.println("BinaryObserver update");
    }
}

class HexaObserver extends BaseObserver{

    public HexaObserver(Subject subject){
        this.subject=subject;
    }


    @Override
    public void update() {
        System.out.println("HexaObserver update");
    }
}


public class Observer {
    
    public static void main(String[]args){

        
        ConcreteSubject subject=new ConcreteSubject();
        BaseObserver hexaobserver=new HexaObserver(subject);
        BaseObserver binaryObserver=new BinaryObserver(subject);

        //添加观察者
        subject.attach(hexaobserver);
        subject.attach(binaryObserver);

        subject.setState(1);
        subject.notifyall();

    }
}

输出：

HexaObserver update
BinaryObserver update