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。

  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();
        }
    }