0105-里氏转换

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

namespace _06里氏转换
{
    class Program
    {
        /*
         * is 返回布尔类型
         * as 转换成功返回对象，否则返回null
         */
        static void Main(string[] args)
        {
            //里氏转换（装箱和拆箱）
            Person p = new Teacher();
            if (p is Teacher)
            {
                Teacher th = p as Teacher;
                if (th != null)
                    th.TeacherSayHello();
            }
            Person p1 = new Student();
            if (p1 is Student)
            {
                ((Student)p1).StudentSayHello();
            }
            //虚方法演示
            Employer[] em = {new Employer(), new Manager(), new Programer()};
            foreach (var e in em)
            {
               e.SignIn(); //输出：员工9点打卡，经理8点打卡，程序员不打卡
            }
            Console.ReadKey();
        }
    }

    class Person
    {
        public void SayHello()
        {
            Console.WriteLine("我是人类");
        }
    }

    class Teacher : Person
    {
        public void TeacherSayHello()
        {
            Console.WriteLine("我是老师");
        }
    }

    class Student : Person
    {
        public void StudentSayHello()
        {
            Console.WriteLine("我是学生");
        }
    }
    //虚方法使用关键字virtual声明,子类使用override覆盖重写
    class Employer
    {
        public virtual void SignIn() {
            Console.WriteLine("员工9点打卡");
        }
    }

    class Manager : Employer
    {
        public override void SignIn()
        {
            Console.WriteLine("经理8点打卡");
        }
    }
    class Programer : Employer
    {
        public override void SignIn()
        {
            Console.WriteLine("程序员不打卡");
        }
    }
}