public class Animal

    {

        public string word="";

        //virtual表示虚方法，用以被重写

        public virtual void say(){ word = "I am an animal.";}

    }

    //override表示重写(覆盖)

    public class Cat : Animal

    {

        public override void say(){ word = "I am a cat.";}

    }

    public class Dog : Animal

    {

        public new void say(){ word = "I am a dog.";}

    }

Animal animal = new Cat();

animal.say();

alert(animal.word);

Cat animal = new Cat();

animal.say();

alert(animal.word);

Animal animal = new Dog();

animal.say();

alert(animal.word);

Dog animal = new Dog();

animal.say();

alert(animal.word);