C# 学习历程——类的封装，继承与多态

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

namespace ConsoleApplication2
{
    class Program
    {
        class A
        {   
            public virtual void Word()
            {
                Console.WriteLine("A");
            }
        
        }

        class B : A
        {
            public new void Word()
            {
                Console.WriteLine("B");
            }

        }
        class C : B
        {
            public virtual void Word()
            {
                Console.WriteLine("C");
            }

        }

        class D : A
        {
            public override void Word()
            {
                Console.WriteLine("D");
            }

        }

        static void Main(string[] args)
        {
            A a1 = new A();
            B b1 = new B();
            C c1 = new C();
            D d1 = new D();
            A b2 = new B();
            A c2 = new C();
            A d2 = new D();
            a1.Word();
            b1.Word();
            c1.Word();
            d1.Word();
            b2.Word();
            c2.Word();
            d2.Word();
            
        }
    }
}