设计模式之观察者模式(Observer)

在看源码的时候我们经常会看到Observer、Listener、Hook、callback等单词，不要被这些词所迷惑，实际上说的都是观察者模式，

观察模式解决方案图如下:

 具体代码:

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

/**
 * 有很多时候，观察者需要根据事件的具体情况来进行处理
 * 大多数时候，我们处理事件的时候，需要事件源对象
 * 事件也可以形成继承体系
 */

class Child {
    private boolean cry = false;
    private List<Observer> observers = new ArrayList<>();

    {
        observers.add(new Dad());
        observers.add(new Mum());
        observers.add(new Dog());
　　　　　observers.add(e -> System.out.println("ppp"));

//hook callback function  } public boolean isCry() { return cry; } public void wakeUp() { cry = true; wakeUpEvent event = new wakeUpEvent(System.currentTimeMillis(), "bed", this); for(Observer o : observers) { o.actionOnWakeUp(event); } } } abstract class Event<T> { abstract T getSource(); } class wakeUpEvent extends Event<Child>{ long timestamp; String loc; Child source; public wakeUpEvent(long timestamp, String loc, Child source) { this.timestamp = timestamp; this.loc = loc; this.source = source; } @Override Child getSource() { return source; } } interface Observer { void actionOnWakeUp(wakeUpEvent event); } class Dad implements Observer { public void feed() { System.out.println("dad feeding..."); } @Override public void actionOnWakeUp(wakeUpEvent event) { feed(); } } class Mum implements Observer { public void hug() { System.out.println("mum hugging..."); } @Override public void actionOnWakeUp(wakeUpEvent event) { hug(); } } class Dog implements Observer { public void wang() { System.out.println("dog wang..."); } @Override public void actionOnWakeUp(wakeUpEvent event) { wang(); } } public class Main { public static void main(String[] args) { Child c = new Child(); //do sth  c.wakeUp(); } }