一、我的了解
觀察者模式是實作一個類與類之間一對多的關系,一個類與多個類之間有互相依賴關系,當該類發生變化時,其他的類會立馬接收到響應
二、實作方式
在單一的類中存儲所有觀察者對應的執行個體,當該類發生變化時,通知所有觀察者相應的變化
三、執行個體
Java執行個體
Subject類:主題類,被觀察的類,它内部維護了一個觀察者的清單,用于在發生變化時通知觀察者
package com.study.dp.observer;
import java.util.ArrayList;
import java.util.List;
public class Subject {
private List<Observer> observers = new ArrayList<>();
private int state;
public int getState() {
return state;
}
public void setState(int state) {
this.state = state;
notifyAllObservers();
}
public void attach(Observer observer) {
observers.add(observer);
}
public void notifyAllObservers() {
for(Observer observer:observers) {
observer.update();
}
}
}
Observer類:觀察者的抽象類,所有觀察者繼承該類,它其中有一個主題類的對象,用于表示該類觀察的對象是哪個,同時也用于在建立觀察者執行個體時将對象綁定到主題類對象中
package com.study.dp.observer;
public abstract class Observer {
protected Subject subject;
public abstract void update();
}
BinaryObserver類:實際的觀察者類
package com.study.dp.observer;
public class BinaryObserver extends Observer {
public BinaryObserver(Subject subject) {
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println("Binary String: "+Integer.toBinaryString(subject.getState()));
}
}
OctalObserver類:實際的觀察者類
package com.study.dp.observer;
public class OctalObserver extends Observer {
public OctalObserver(Subject subject) {
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println("Octal String: "+Integer.toOctalString(subject.getState()));
}
}
HexaObserver類:實際的觀察者類
package com.study.dp.observer;
public class HexaObserver extends Observer {
public HexaObserver(Subject subject) {
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println("Hex String: "+Integer.toHexString(subject.getState()));
}
}
Demo類:測試
package com.study.dp.observer;
public class Demo {
public static void main(String[] args) {
Subject subject = new Subject();
new HexaObserver(subject);
new OctalObserver(subject);
new BinaryObserver(subject);
System.out.println("First state change: 15");
subject.setState(15);
System.out.println("Second state change: 10");
subject.setState(10);
}
}
四、應用場景
- nodejs的事件驅動模型