当对象间存在一对多关系时,则使用观察者模式(Observer Pattern)。比如,当一个对象被修改时,则会自动通知它的依赖对象。观察者模式属于行为型模式。
UML图片
1.创建Subject类
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();
}
}
}
2.创建Observer类
public abstract class Observer{
protected Subject subject;
public abstract void update();
}
3.创建实体观察者类
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"+subject.getState());
}
}
4.使用
public class ObserverPatternDmeo{
public static void main(String[] args){
Subject subject = new Subject();
new BinaryObserver(subject);
subject.setState(14);
}
}