interface

interface Ishirou
    {       
        void Hunt();
    }
    interface Ishicao
    {
        void EatGrass();
    }
    abstract class Animal
    {
        public abstract void Eat();     
    }
    class Cat : Animal,Ishirou
    {
        public override void Eat() { Console.WriteLine("猫吃鱼"); }  
        public void Hunt()
        {
            Console.WriteLine("猫捉老鼠");           
        }
    }
    class Tiger : Animal, Ishirou
    {
        public override void Eat() { Console.WriteLine("老虎也吃鱼"); }
        public void Hunt()
        {
            Console.WriteLine("老虎捉羊");
        }
    }
    class Sheep : Animal, Ishicao
    {
        public override void Eat() { Console.WriteLine("羊吃草"); }  
        public void EatGrass()
        {          
        }
    }

    class Program
    {       
        static void Main(string[] args)
        {  
            List<Animal> animals = new List<Animal>();
            Animal a1 = new Cat();
            animals.Add(a1);
            Animal a2 = new Sheep();
            animals.Add(a2);
            Animal a3 = new Sheep();
            animals.Add(a3);
            Animal a4 = new Tiger();
            animals.Add(a4);          

            foreach (Animal a in animals)
            {
                if (a is Ishirou)
                {
                    Ishirou irou = (Ishirou)a;                    
                    irou.Hunt();
                }
            }
                        
        }
    }