C#多态及接口

直接看代码吧

using System;
using static System.Console;

namespace ConsoleApp
{
    //使用abstract，抽象类或方法，不能使用virtual，派生类必须实现所有抽象方法
    abstract class Shape
    {
        public int Size { get; set; }

        public  virtual void Draw()
        {
            WriteLine("shap");
        }
    }
    //密封类(方法)，就不能派生（重写） string类为密封的
    sealed class Rect: Shape
    {
        public override void Draw()
        {
            WriteLine("rect");
            //base.Draw();
        }
    }
    //接口 相当于抽象类
    //不能声明成员的修饰符，成员总是public，不能声明为virtual
    //接口也可以彼此继承，从而添加新的声明
    public interface IMyInterface
    {
        //可以包含方法、属性、索引器和事件的声明，不能实现
        void Draw();
        int Size { get; set; }

    }
    //继承接口的类必须实现接口的所有东西
    class A : IMyInterface
    {
        public void Draw()
        {
            WriteLine('A');
        }
        private int _size;
        public int Size
        {
            get
            {
                return _size;
            }
            set
            {
                _size = value;
            }
        }
    }

    class B : IMyInterface
    {
        public void Draw()
        {
            WriteLine('B');
        }
        private int _size;
        public int Size
        {
            get
            {
                return _size;
            }
            set
            {
                _size = value;
            }
        }
    }

    class Program
    {
        public void as_is(object o)
        {
            //1 ,如果该object类型不对就会引发InvalidCastException异常
            IMyInterface myinterface = (IMyInterface)o;
            myinterface.Draw();

            //2 as
            IMyInterface myinterface1 = o as IMyInterface;
            if (myinterface1 != null)
            {
                myinterface1.Draw();
            }

            //3 is
            if (o is IMyInterface)
            {
                IMyInterface myinterface2 = (IMyInterface)o;
                myinterface2.Draw();
            }

        }

        static void Main(string[] args)
        {
            Shape s = new Rect();
            s.Draw();

            //接口可以引用任何实现该接口的类
            IMyInterface a = new A();
            IMyInterface b = new B();

            a.Draw();
            b.Draw();

        }
    }
}