设计模式11——观察者模式

1. 定义

当一个对象（被观察对象）被修改时，则会自动通知它的依赖对象。

2. 类图

在这里插入图片描述

3. 实现

3.1 `Subject` 被观察者类

package observer;

import java.util.ArrayList;
import java.util.List;

public class Subject {
    private int state;
    public List<Observer> observerList = new ArrayList<Observer>();;

    public int getState() {
        return state;
    }

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

    public void attach(Observer observer) {
        observerList.add(observer);
    }
    private void notifyAllObserver() {
        for(Observer observer: observerList)
            observer.update();
    }
}

成员变量：

state：标志状态
List<Observer> observerList ：观察者们，用于存放观察者们的集合

在setState(int state)方法中状态改变，因此在该方法中调用私有方法通知所有观察者进行对应的操作

3.2 `Observer`观察者类

package observer;

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

抽象类，成员变量用于关联观察者和被观察者的关系

3.3 `OctalObserver`类

package observer;

public class OctalObserver extends Observer {

    public OctalObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("OctalObserver：  " + Integer.toOctalString(subject.getState()));
    }
}

3.4 `BinaryObserver`类

package observer;

public class BinaryObserver extends Observer {
    public BinaryObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("BinaryObserver: " + Integer.toBinaryString(subject.getState()));
    }
}

3.5 `HexaObserver` 类

package observer;

public class HexaObserver extends Observer{
    public HexaObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("HexaObserver : " + Integer.toHexString(this.subject.getState()));
    }
}

3.6 `Main`类

package observer;

public class Main {
    public static void main(String[] args) {
        Subject subject = new Subject();
        new OctalObserver(subject);
        new BinaryObserver(subject);
        new HexaObserver(subject);
        System.out.println("subject的state值为15.。。");
        subject.setState(15);
    }
}