程序设计: 猫大叫一声，所有的老鼠都开始逃跑，主人被惊醒。(C#语言)
要求：  
1.要有联动性，老鼠和主人的行为是被动的。
2.考虑可扩展性，猫的叫声可能引起其他联动效应。


 要点：1. 联动效果，运行代码只要执行Cat.Cryed()方法。

　　    2. 对老鼠和主人进行抽象

  1 public interface Observer  2     {  3         void Response();    //观察者的响应，如是老鼠见到猫的反映  4     }  5     public interface Subject  6     {  7         void AimAt(Observer obs);  //针对哪些观察者，这里指猫的要扑捉的对象---老鼠  8     }  9     public class Mouse : Observer 10     { 11         private string name; 12         public Mouse(string name, Subject subj) 13         {            14             this.name = name; 15             subj.AimAt(this); 16         } 17          18         public void Response() 19         { 20             Console.WriteLine(name + " attempt to escape!"); 21         } 22     } 23     public class Master : Observer 24     {    25         public Master(Subject subj) 26         {            27             subj.AimAt(this); 28         } 29          30         public void Response() 31         { 32             Console.WriteLine("Host waken!"); 33         }   34     } 35   36     public class Cat : Subject 37     { 38         private ArrayList observers; 39         public Cat() 40         {    41             this.observers = new ArrayList(); 42         } 43         public void AimAt(Observer obs) 44         { 45             this.observers.Add(obs); 46         } 47         public void Cry() 48         { 49             Console.WriteLine("Cat cryed!"); 50             foreach (Observer obs in this.observers) 51             { 52                 obs.Response(); 53             } 54         } 55     } 56     class MainClass 57     {        58         static void Main(string[] args) 59         { 60             Cat cat = new Cat(); 61             Mouse mouse1 = new Mouse("mouse1", cat); 62             Mouse mouse2 = new Mouse("mouse2", cat); 63             Master master = new Master(cat); 64             cat.Cry(); 65         } 66     } 67  68  69 //--------------------------------------------------------------------------------------------- 70  71 设计方法二: 使用event -- delegate设计.. 72     public delegate void SubEventHandler(); 73     public abstract class Subject 74     { 75         public event SubEventHandler SubEvent; 76         protected void FireAway() 77         { 78             if (this.SubEvent != null) 79                 this.SubEvent(); 80         }    81     } 82     public class Cat : Subject 83     {   84         public void Cry() 85         { 86             Console.WriteLine("cat cryed."); 87             this.FireAway(); 88         } 89     } 90     public abstract class Observer 91     { 92         public Observer(Subject sub) 93         { 94             sub.SubEvent += new SubEventHandler(Response); 95         } 96         public abstract void Response();     97     } 98     public class Mouse : Observer 99     {100         private string name;101         public Mouse(string name, Subject sub) : base(sub)102         {   103             this.name = name;104         }105         public override void Response()106         {107             Console.WriteLine(name + " attempt to escape!");108         }109     }110     public class Master : Observer111     {112         public Master(Subject sub) : base(sub){}113         public override void Response()114         {115             Console.WriteLine("host waken");116         }117     }118     class Class1119     {120         static void Main(string[] args)121         {122             Cat cat = new Cat();123             Mouse mouse1 = new Mouse("mouse1", cat);124             Mouse mouse2 = new Mouse("mouse2", cat);125             Master master = new Master(cat);126             cat.Cry();127         }128 129     } 

猫大叫一声，所有的老鼠都开始逃跑，主人被惊醒