1 package ObserverPattern;
 2
 3 import java.util.ArrayList;
 4 import java.util.List;
 5
 6 public abstract class Subject {
 7
 8     //define an ArrayList to store observers
 9     private List<Observer>  observers = new ArrayList<>();
10     public List<Observer> getObservers() {
11         return observers;
12     }
13
14
15     public void join(Observer observer) {
16         observers.add(observer);
17     }
18
19     public void quit(Observer observer) {
20         observers.remove(observer);
21     }
22
23     public abstract void notifyObservers(String name);
24
25 }

package ObserverPattern;public abstract class Observer {protected Subject subject;public Observer(Subject subject) {this.subject = subject;}public abstract void sysMsg(String msg);public abstract void beAttacked();public abstract String getName();public abstract void setName(String name);
}

package ObserverPattern;public class ActionControlCenter extends Subject {@Overridepublic void notifyObservers(String name) {for (Observer observer : getObservers()) {if (name.equals(observer.getName()))observer.sysMsg(observer.getName() +"收到消息：坚持住，你队友正在赶来！");elseobserver.sysMsg(observer.getName() +"收到消息：我方\"" + name + "\"正在受到攻击，请尽快支援！");}}
}

package ObserverPattern;public class Player extends Observer {public Player(Subject subject) {super(subject);}private String name;public void setName(String name) {this.name = name;}public String getName() {return name;}@Overridepublic void beAttacked() {System.out.println(getName() + "收到消息：您正在受到攻击！");subject.notifyObservers(getName());}@Overridepublic void sysMsg(String msg) {System.out.println(msg);}
}