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 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
评分标准: <1>.构造出Cat、Mouse、Master三个类，并能使程序运行(2分)
            <2>从Mouse和Master中提取抽象（5分）
            <3>联动效应，只要执行Cat.Cryed()就可以使老鼠逃跑，主人惊醒。(3分)

    public interface Observer
    {
        void Response();    //观察者的响应，如是老鼠见到猫的反映
    }
    public interface Subject
    {
        void AimAt(Observer obs);  //针对哪些观察者，这里指猫的要扑捉的对象---老鼠
    }
    public class Mouse : Observer
    {
        private string name;
        public Mouse(string name, Subject subj)
        {          
            this.name = name;
            subj.AimAt(this);
        }
       
        public void Response()
        {
            Console.WriteLine(name + " attempt to escape!");
        }
    }
    public class Master : Observer
    {  
        public Master(Subject subj)
        {          
            subj.AimAt(this);
        }
       
        public void Response()
        {
            Console.WriteLine("Host waken!");
        } 
    }
 
    public class Cat : Subject
    {
        private ArrayList observers;
        public Cat()
        {  
            this.observers = new ArrayList();
        }
        public void AimAt(Observer obs)
        {
            this.observers.Add(obs);
        }
        public void Cry()
        {
            Console.WriteLine("Cat cryed!");
            foreach (Observer obs in this.observers)
            {
                obs.Response();
            }
        }
    }
    class MainClass
    {      
        static void Main(string[] args)
        {
            Cat cat = new Cat();
            Mouse mouse1 = new Mouse("mouse1", cat);
            Mouse mouse2 = new Mouse("mouse2", cat);
            Master master = new Master(cat);
            cat.Cry();
        }
    }

//---------------------------------------------------------------------------------------------

设计方法二: 使用event -- delegate设计..
    public delegate void SubEventHandler();
    public abstract class Subject
    {
        public event SubEventHandler SubEvent;
        protected void FireAway()
        {
            if (this.SubEvent != null)
                this.SubEvent();
        }  
    }
    public class Cat : Subject
    { 
        public void Cry()
        {
            Console.WriteLine("cat cryed.");
            this.FireAway();
        }
    }
    public abstract class Observer
    {
        public Observer(Subject sub)
        {
            sub.SubEvent += new SubEventHandler(Response);
        }
        public abstract void Response();   
    }
    public class Mouse : Observer
    {
        private string name;
        public Mouse(string name, Subject sub) : base(sub)
        {  
            this.name = name;
        }
        public override void Response()
        {
            Console.WriteLine(name + " attempt to escape!");
        }
    }
    public class Master : Observer
    {
        public Master(Subject sub) : base(sub){}
        public override void Response()
        {
            Console.WriteLine("host waken");
        }
    }
    class Class1
    {
        static void Main(string[] args)
        {
            Cat cat = new Cat();
            Mouse mouse1 = new Mouse("mouse1", cat);
            Mouse mouse2 = new Mouse("mouse2", cat);
            Master master = new Master(cat);
            cat.Cry();
        }

    }

========================================================

interface用来声明接口
1.只提供一些方法规约，不提供方法主体
  如
  public interface IPerson
 {
  void getName();//不包含方法主体
  }
2.方法不能用public abstract等修饰,无字段变量，无构造函数。
3.方法可包含参数
  如 
  public interface IPerson
  {
   void getAge(string s);
  }

  一个例子(例1)：
  public interface IPerson
  {
   IPerson();              //错误
   string name;            //错误
   public void getIDcard();//错误

   void getName();         //right
   void getAge(string s);  //right
   }

实现interface的类
1.与继承类的格式一致，如 public class Chinese:IPerson{}
2.必须实现interface中的各个方法

   例2，继承例1
    public class Chinese:IPerson
  {
   public Chinese(){}             //添加构造
   public void getName(){}        //实现getName()
   public void getAge(string s){} //实现getAge()
   }