一道有趣的面试题 - 设计模式的运用

  程序设计: 猫大叫一声，所有的老鼠都开始逃跑，主人被惊醒。

 

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。

 

程序员甲是这样设计的: 

    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，这里指猫的要捕捉的对象---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(); 
        } 
    } 

 

程序员乙的设计方案是技高一筹

       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");
            }
        }
      
        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();
        }