using System; using System.Collections.Generic; using System.Text; namespace ConsoleApplication1 {     class IsOrAsClass     {         class Animal         {             public void Eat()             {                 Console.WriteLine("Eating...");             }             public override string ToString()             {                return  "I am Eating";             }         }         //家禽类         class jia:Animal         {         }         //狗         class Dog : jia         {         }         //鸟         class bird         {         }         static void Main()         {            IsOrAsClass app=new IsOrAsClass();            //            Dog d=new Dog();            app.UseIsOpreate(d);            app.UseAsOpreate(d);            //            bird b = new bird();            app.UseAsOpreate(b);         }         //使用Is运算符         void UseIsOpreate(Animal a)         {             if (a is jia)             {                 jia j = (jia)a;                 j.Eat();             }         }         //使用AS运算符         void UseAsOpreate(object o)         {             jia j = o as jia;             if (j != null)             {                 Console.WriteLine(j.ToString());             }             else             {                 Console.WriteLine("{0} is not Animal", o.GetType().Name);             }         }     } }