C#类的继承

    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.";}
    }

上面的三个类（Cat，Dog，Cow）继承类Animal。下面进行几种实例化测试：

1.

Animal animal = new Cat();
animal.say();
alert(animal.word);

输出的是 “I am a cat.”

2.

Cat animal = new Cat();
animal.say();
alert(animal.word);

输出的也是 “I am a cat.” 

3.

Animal animal = new Dog();
animal.say();
alert(animal.word);

输出的是“I am an animal” ，

4.

Dog animal = new Dog();
animal.say();
alert(animal.word);

输出的是“I am an dog”

ps：上面可以看出override和new形式的区别