觀察者設定一個觀察目標，根據觀察目標的變化，觀察者采取相應的應對行為---觀察者模式

 1 //玩家類
 2 public class Player {
 3     
 4     private String name;
 5     private Team t;
 6     
 7     public Player(String name){
 8         this.name = name;
 9     }
10     
11     public String getName(){
12         return name;
13     }
14     
15
 
     public void setTeam(Team t){
16         this.t= t;
17     }
18     
19     //如果玩家被攻擊，通知遊戲中心進行呼救
20     public void beAttacked(Controller c){
21         System.out.println(name + "被攻擊~速來援助~");
22         c.noticeOther(t,name);
23         
24     }
25 
26     //用來援助隊友的
27     public void help(){
28         System.out.println("挺住！" + name + "來也~~~");
 
29     }
30 }
31 
32 //戰隊類
33 import java.util.ArrayList;
34 import java.util.List;
35 
36 public class Team {
37     
38     @SuppressWarnings("unused")
39     private String name;
40     
41     private List<Player> players = new ArrayList<Player>();
42     
43     public Team(String name){
 
44         this.name = name;
45         System.out.println(name + "戰隊組建成功！");
46     }
47     
48     public void join(Player p){
49         this.players.add(p);
50         p.setTeam(this);
51     }
52 
53     public void help(String name) {
54         for (Player player : players) {
55             if (!player.getName().equals(name)) {
56                 player.help();
57             }
58         }
59     }
60 
61 }
62 
63 //遊戲中心
64 public class Controller {
65         
66     public void noticeOther(Team t,String name){
67         t.help(name);
68     }
69 
70 }
71 
72 
73 //
74 public class ObserverTestDemo {
75 
76     public static void main(String[] args) {
77 
78         Controller c = new Controller();
79 
80         Team t = new Team("金庸");
81 
82         Player p1 = new Player("令狐沖");
83         t.join(p1);
84         Player p2 = new Player("張無忌");
85         t.join(p2);
86         Player p3 = new Player("東方不敗 ");
87         t.join(p3);
88         Player p4 = new Player("楊過");
89         t.join(p4);
90 
91         p1.beAttacked(c);
92     }
93 
94 }

java觀察者模式