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("\nJourney by car");
             Car mycar = new Car();
             mycar.StartEngine("gogo");
             mycar.SpeedUp();
             mycar.Drive();
             mycar.SpeedDown();
             mycar.StopEngine("stop");

             Console.WriteLine("\nTest");
             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。