C#之virtual override new解析

温故而知新，是智也。

virtual允许派生类重写该方法。默认情况下方法是非虚的，不允许重写。

override重写基类具有相同签名的方法，不可重写非虚方法和静态方法，对应基类同名方法的关键字是virtual、abstract。

new常用于：作为运算符，创建对象及调用构造函数；作为修饰符，隐藏基类具有相同签名的方法；用于泛型约束，约束参数类型。

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

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            MyChild mychild = new MyChild();
            MyBase mybase1 = new MyBase();
            MyBase mybase2 = mychild;

            mybase1.Say();  //MyBase.Say
            mybase2.Say();  //MyBase.Say
            mychild.Say();  //MyChild.Say

            mybase1.Speak();    //MyBase.Speak
            mybase2.Speak();    //MyChild.Speak，注意这里不是MyBase.Speak
            mychild.Speak();    //MyChild.Speak

            mybase1.Talk(); //MyBase.Talk
            mybase2.Talk(); //MyBase.Talk
            mychild.Talk(); //MyChild.Talk

            mybase1.Tell(); //MyBase.Tell
            mybase2.Tell(); //MyBase.Tell
            mychild.Tell(); //MyChild.Tell

            Console.ReadKey();
        }
    }

    class MyBase
    {
        public virtual void Say() { Console.WriteLine("MyBase.Say"); }
        public virtual void Speak() { Console.WriteLine("MyBase.Speak"); }
        public virtual void Talk() { Console.WriteLine("MyBase.Talk"); }
        public void Tell() { Console.WriteLine("MyBase.Tell"); }
    }
    class MyChild : MyBase
    {
        public new void Say() { Console.WriteLine("MyChild.Say"); }    //new修饰符显式隐藏基类方法
        public override void Speak() { Console.WriteLine("MyChild.Speak"); }   //override修饰符重写基类方法
        public void Talk() { Console.WriteLine("MyChild.Talk"); }   //隐式隐藏基类方法
        public void Tell() { Console.WriteLine("MyChild.Tell"); }   //隐式隐藏基类方法
    }
}