C#学习记录3下——类的封装，继承，多态

new,virtual,override三者的区别

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            Shape shap1 = new Shape();
            shap1.Draw();
            Polygon poly1 = new Polygon();
            poly1.Draw();
            Rectangle rect1 = new Rectangle();
            rect1.Draw();
            Shape polyAsShape = new Polygon();
            polyAsShape.Draw();
            Shape rectAsShape = new Rectangle();
            rectAsShape.Draw();
            Polygon rectAsPoly = new Rectangle();
            rectAsShape.Draw();
            Console.ReadKey();
        }
        class Shape
        {
            public virtual void Draw()
            {
                Console.WriteLine("Inside Shape");
            }
        }
        class Polygon : Shape
        {
            public new virtual void Draw()
            {
                Console.WriteLine("Inside Polygon");
            }
        }
        class Rectangle : Polygon
        {
            public virtual void Draw()
            {
                Console.WriteLine("Inside Rectangle");
            }
        }
    }
}

从上面的结果可以看出

通过new定义的子类方法，如果子类的具体实例是子类类型（poly1），则调用子类中的重写函数；子类实例是父类类型（即polyAsShape），则调用父类中的重写函数。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            Shape shap1 = new Shape();
            shap1.Draw();
            Polygon poly1 = new Polygon();
            poly1.Draw();
            Rectangle rect1 = new Rectangle();
            rect1.Draw();
            Shape polyAsShape = new Polygon();
            polyAsShape.Draw();
            Shape rectAsShape = new Rectangle();
            rectAsShape.Draw();
            Polygon rectAsPoly = new Rectangle();
            rectAsShape.Draw();
            Console.ReadKey();
        }
        class Shape
        {
            public virtual void Draw()
            {
                Console.WriteLine("Inside Shape");
            }
        }
        class Polygon : Shape
        {
            public override void Draw()
            {
                Console.WriteLine("Inside Polygon");
            }
        }
        class Rectangle : Polygon
        {
            public override void Draw()
            {
                Console.WriteLine("Inside Rectangle");
            }
        }
    }
}

上面的结果说明

override无论子类的实例是父类类型还是子类类型，子类的实例都会调用子类中重写的函数。其实override可以对父类的所有方法进行覆盖，不一定是virtual