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

namespace Virtualdemo
{
  class Program
  {
    static void Main(string[] args)
    {//BClass A = new BClass(); 抽象类无法被实例
      Class1 c = new Class1();
      BClass c2 = c;
      c2.MethodA();
      c.MethodA();
      c2.MethodB();
      c.MethodB();
      c2.MethodC();
      c.MethodC();
      Console.ReadKey();
    }
  }
  abstract class BClass  //抽象类无法被实例
  {
    public virtual void MethodA() { Console.WriteLine("BClassA"); }
    public virtual void MethodB() { Console.WriteLine("BClassB"); }
    public virtual void MethodC() { Console.WriteLine("BClassC"); }
  }
  class Class1 : BClass
  {
    public void MethodA() { Console.WriteLine("MethodA"); }//如果一个虚函数 在子类中没有通过override关键字，那么这个方法就没有被重写，而是被隐藏了
    public override void MethodB() { Console.WriteLine("MethodB"); }
    public override void MethodC() { base.MethodC(); }
  }
}

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

namespace Virtualdemo
{
  class Program
  {
    static void Main(string[] args)
    {
      Teacher t = new Teacher();
      Student stu = t;
      stu.Exam();
      stu.Say();
      t.Say();
      Console.ReadKey();
    }
  }
  public abstract class Student
  {
    public virtual void Exam()
    {
      Console.WriteLine("学生都要考试");
    }
    public void Say()
    {
      Console.WriteLine("我是学生");
    }
  }
  public class Teacher : Student
  {
    public override void Exam()
    {
      Console.WriteLine("老师不用考试");
    }
    //public override void Say() //报错，提示没有virtual,无法被重写
    //{
    //  Console.WriteLine("我是老师");
    //}
    public new void Say()
    {
      Console.WriteLine("我是老师");
    }
  }
}