一道有趣的C#面试题

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

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();

}

}