C#父类子类对象关系

案例：

主要有Vehicle.cs  Airplane.cs   Car.cs  3个类。

Car和Airplane都继承与Vehicle类。Vehicle中Drive为虚方法，可在子类中重写，父类引用子类对象，并在car中重写了Drive方法。

 class Vehicle
    {
        public void StartEngine(string noiseToMakeWhenStaring)
        {
            Console.WriteLine("starting engine:{0}",noiseToMakeWhenStaring);
        }

        public void StopEngine(string noiseToMakeWhenStopping)
        {
            Console.WriteLine("stopping engine:{0}",noiseToMakeWhenStopping);
        }

        public virtual void Drive()
        {
            Console.WriteLine("Default Drive method");
        }
    }

    class Airplane :Vehicle
    {
        public void Takeoff(){
            Console.WriteLine("take off");
        }
        public void Land()
        {
            Console.WriteLine("land");
        }
    }

    class Car:Vehicle
    {
        public void SpeedUp()
        {
            Console.WriteLine("SpeedUp");
        }

        public void SpeedDown()
        {
            Console.WriteLine("SpeedDown");
        }

        public override void Drive()//重写父类Drive中的方法
        {
            Console.WriteLine("Motoring");
        }
    }

Program.cs

using System;

namespace Vehicles
{
    class Program
    {
        static void DoWork()
        {
            Console.WriteLine("Journey by airplane:");
            Airplane myplane = new Airplane();
            myplane.StartEngine("Contact");
            myplane.Takeoff();
            myplane.Drive();
            myplane.Land();
            myplane.StopEngine("whirr");

            Console.WriteLine("
Journey by car");
            Car mycar = new Car();
            mycar.StartEngine("gogo");
            mycar.SpeedUp();
            mycar.Drive();
            mycar.SpeedDown();
            mycar.StopEngine("stop");

            Console.WriteLine("
Test");
            Vehicle v = mycar;//父类引用子类对象；
            v.Drive();   //运行为子类中重写的方法
            v = myplane;
            v.Drive();
        }

        static void Main()
        {
            try
            {
                DoWork();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception: {0}", ex.Message);
            }
            Console.ReadKey();
        }
    }
}

注意：

在program中父类可以引用子类对象复制，类的赋值的原则是，子类型可以赋值给父类型，反之需要进行强制转换。在子类中是用override可以重构父类的方法，代码执行过程中，会引用子类中重构的父类方法。