一道有趣的C#面試題

程式設計: 貓大叫一聲，所有的老鼠都開始逃跑，主人被驚醒。(C#語言)

要求： 
1.要有聯動性，老鼠和主人的行為是被動的。

2.考慮可擴充性，貓的叫聲可能引起其他聯動效應。

要點：1. 聯動效果，運行代碼只要執行Cat.Cryed()方法。2. 對老鼠和主人進行抽象
評分標準: <1>.構造出Cat、Mouse、Master三個類，並能使程式運行(2分)
            <2>從Mouse和Master中提取抽象（5分）
            <3>聯動效應，只要執行Cat.Cryed()就可以使老鼠逃跑，主人驚醒。(3分)

    public interface Observer
    {
        void Response();    //觀察者的響應，如是老鼠見到貓的反映
    }
    public interface Subject
    {
        void AimAt(Observer obs);  //針對哪些觀察者，這裡指貓的要撲捉的對象---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();
        }
    }

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

設計方法二: 使用event -- delegate設計..
    public delegate void SubEventHandler();
    public abstract class Subject
    {
        public event SubEventHandler SubEvent;
        protected void FireAway()
        {
            if (this.SubEvent != null) 
            &nbsp;       

            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();
        }

    }