大话设计模式-观察者模式

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• 当ConcreteSubject的状态发生改变时，会调用其内部的方法Notify(),该方法内部会对每一个监听它的观察者发出update通知

/**
 * 观察者接口
 * 可以针对某个通知做出反应
 */
public interface Observer {
    void update();
}

/**
 * 具体的观察者
 */
public class ConcreteObserver implements Observer {

    /**
     * 1.观察者名字
     * 2.观察者状态
     * 3.具体的通知者
     */
    private String name;
    private String observerState;
    private ConcreteSubject concreteSubject;

    public ConcreteObserver(String name, ConcreteSubject concreteSubject) {
        this.name = name;
        this.concreteSubject = concreteSubject;
    }

    @Override
    public void update() {
        observerState = concreteSubject.getSubjectState();
        System.out.println("观察者 " + name + " 的新状态是 " + observerState);
    }
}

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

/**
 * 抽象通知者
 * 可以有多个观察者接收它发出的通知
 */
public abstract class Subject {

    private List<Observer> observers = new ArrayList<>();


    public void add(Observer observer) {
        observers.add(observer);
    }

    public void remove(Observer observer) {
        observers.remove(observer);
    }

    public void Notify() {
        for (Observer observer : observers) {
            observer.update();
        }
    }

}

/**
 * 具体的观察者
 */
public class ConcreteSubject extends Subject {
    //具体被观察者状态
    private String subjectState;

    public String getSubjectState() {
        return subjectState;
    }

    public void setSubjectState(String subjectState) {
        this.subjectState = subjectState;
    }
}

public class Main {
    public static void main(String[] args) {
        ConcreteSubject concreteSubject = new ConcreteSubject();
        concreteSubject.add(new ConcreteObserver("A",concreteSubject));
        concreteSubject.add(new ConcreteObserver("B",concreteSubject));
        concreteSubject.add(new ConcreteObserver("C",concreteSubject));

        concreteSubject.setSubjectState("改变的状态");
        concreteSubject.Notify();
    }
}