C#学习笔记07：多态

1、多态性概念

使用同一个名称，其依据Context不同，产生不同功能。如对象调用同一函数，随着引用实例不同，实现功能也不相同。
Shape shape=newCirlce();
      shape.area();
shape=new Rect();
      shape.area();
在OOP编程中，实现多态一般通过子类重写父类中虚函数或抽象函数来实现，
abstract class Shape{
    public abstractdouble area();
    public void disp(){
       …
    }
}
抽象类不能实例化.(基类)
class Circle :Shape{
    public overridedouble area(){
       ..
    }
 }

2、接口Interface定义与使用

   接口是一种特殊类，接口中只有抽象函数与抽象属性声明。
 1)接口定义
   interface IShape
    {
         double area();
         double length();
    }
    class Circle: IShape
    {
        private double r;
        public Circle() { }
        public Circle(double r)
        {
            this.r = r;
        }
        public  double area()
        {
            return Math.PI*r*r;
        }
        public double length()
        {
            return 2 * Math.PI* r;
        }
    }
    class Rect: IShape
    {
        private double w, h;
        public Rect() { }
        public Rect(double w, double h)
        {
            this.w = w; this.h = h;
        }
        public double area()
        {
            return w*h;
        }
        public double length()
        {
            return 2*(w+h);
        }
    }
 例：定义一个会飞接口
   interface ICanFly
    {
        void fly();
    }
    class Bird: ICanFly
    {
        public void fly()
        {
            Console.WriteLine("Bird Flying");
        }
    }
    class Plane: ICanFly
    {
        public void fly()
        {
            Console.WriteLine("Plane Flying");
        }
    }
    class Person
    {
    }
    class Ex1_1
    {
        static void makeFly(Objectobj)
        {
            //Console.WriteLine(obj.GetType());
            //Console.WriteLine(obj.ToString());
            if (obj is ICanFly)
            {
                ICanFly fly = (ICanFly)obj;
                fly.fly();
            }
            else
                Console.WriteLine("Can not fly!");
        }
        static void Main(string[] args)
        {
            Bird bird = new Bird();
            makeFly(bird);
            Plane plane = new Plane();
            makeFly(plane);
            Person person = new Person();
            makeFly(person);
            Console.ReadLine();
        }
    }
本章练习题下载地址：点此下载