版权声明:转载注明出处 https://blog.csdn.net/jy02268879/article/details/81639740
1.自己定义
目录
Observer.java
public interface Observer {
void update(Subject s);
}
ObserverA.java
public class ObserverA implements Observer{
//跟目标对象的state值保持一致
private int myState;
@Override
public void update(Subject s) {
myState = ((ConcreteSubject)s).getState();
}
public int getMyState() {
return myState;
}
public void setMyState(int myState) {
this.myState = myState;
}
}
Subject.java
import java.util.ArrayList;
import java.util.List;
public class Subject {
//订阅这个主题的所有观察者
List<Observer> list= new ArrayList<Observer>();
public void register(Observer obs){
list.add(obs);
}
public void removeObserver(Observer obs){
list.remove(obs);
}
//通知所有观察者
public void notifyAllObservers(){
for(Observer obs : list){
obs.update(this);
}
}
}
ConcreteSubject.java
public class ConcreteSubject extends Subject{
private int state;
public int getState() {
return state;
}
//通知所有观察者
public void setState(int state) {
this.state = state;
this.notifyAllObservers();
}
}
Client.java
public class Client {
public static void main(String[] args) {
//目标对象
ConcreteSubject subject = new ConcreteSubject();
//创建多个观察者
ObserverA obs1 = new ObserverA();
ObserverA obs2 = new ObserverA();
ObserverA obs3 = new ObserverA();
//把这三个观察者添加到Subject对象的观察者中
subject.register(obs1);
subject.register(obs2);
subject.register(obs3);
//改变subject的状态
subject.setState(3000);
//查看观察者的状态是否也改变
System.out.println(obs1.getMyState());
System.out.println(obs2.getMyState());
System.out.println(obs3.getMyState());
}
}
2.使用JDK定义的Observer、Observable
目录
ConcreteSubject.java
import java.util.Observable;
/**
* 使用java提供的Obervable和Observer来实现观察者模式
* */
//目标对象
public class ConcreteSubject extends Observable{
private int state;
public void set(int s){
state = s; //目标对象的状态发生改变
setChanged();//表示目标对象已经做了修改
notifyObservers(state);//通知所有的观察者
}
public int getState() {
return state;
}
public void setState(int state) {
this.state = state;
}
}
ObserverA.java
import java.util.Observable;
import java.util.Observer;
public class ObserverA implements Observer{
private int myState;
@Override
public void update(Observable o, Object arg) {
myState = ((ConcreteSubject)o).getState();
}
public int getMyState() {
return myState;
}
public void setMyState(int myState) {
this.myState = myState;
}
}
Client.java
import com.sid.observer2.ConcreteSubject;
import com.sid.observer2.ObserverA;
public class Client {
public static void main(String[] args) {
//目标对象
ConcreteSubject subject = new ConcreteSubject();
//创建多个观察者
ObserverA obs1 = new ObserverA();
ObserverA obs2 = new ObserverA();
ObserverA obs3 = new ObserverA();
//把这三个观察者添加到Subject对象的观察者中
subject.addObserver(obs1);
subject.addObserver(obs2);
subject.addObserver(obs3);
//改变subject的状态
subject.setState(3000);
//查看观察者的状态是否也改变
System.out.println(obs1.getMyState());
System.out.println(obs2.getMyState());
System.out.println(obs3.getMyState());
}
}