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。

 1  class Vehicle
 2     {
 3         public void StartEngine(string noiseToMakeWhenStaring)
 4         {
 5             Console.WriteLine("starting engine:{0}",noiseToMakeWhenStaring);
 6         }
 7
 8         public void StopEngine(string noiseToMakeWhenStopping)
 9         {
10             Console.WriteLine("stopping engine:{0}",noiseToMakeWhenStopping);
11         }
12
13         public virtual void Drive()
14         {
15             Console.WriteLine("Default Drive method");
16         }
17     }

 1     class Airplane :Vehicle
 2     {
 3         public void Takeoff(){
 4             Console.WriteLine("take off");
 5         }
 6         public void Land()
 7         {
 8             Console.WriteLine("land");
 9         }
10     }

 1     class Car:Vehicle
 2     {
 3         public void SpeedUp()
 4         {
 5             Console.WriteLine("SpeedUp");
 6         }
 7
 8         public void SpeedDown()
 9         {
10             Console.WriteLine("SpeedDown");
11         }
12
13         public override void Drive()//重写父类Drive中的方法
14         {
15             Console.WriteLine("Motoring");
16         }
17     }

Program.cs

 1 using System;
 2
 3 namespace Vehicles
 4 {
 5     class Program
 6     {
 7         static void DoWork()
 8         {
 9             Console.WriteLine("Journey by airplane:");
10             Airplane myplane = new Airplane();
11             myplane.StartEngine("Contact");
12             myplane.Takeoff();
13             myplane.Drive();
14             myplane.Land();
15             myplane.StopEngine("whirr");
16
17             Console.WriteLine("\nJourney by car");
18             Car mycar = new Car();
19             mycar.StartEngine("gogo");
20             mycar.SpeedUp();
21             mycar.Drive();
22             mycar.SpeedDown();
23             mycar.StopEngine("stop");
24
25             Console.WriteLine("\nTest");
26             Vehicle v = mycar;//父类引用子类对象；
27             v.Drive();   //运行为子类中重写的方法
28             v = myplane;
29             v.Drive();
30         }
31
32         static void Main()
33         {
34             try
35             {
36                 DoWork();
37             }
38             catch (Exception ex)
39             {
40                 Console.WriteLine("Exception: {0}", ex.Message);
41             }
42             Console.ReadKey();
43         }
44     }
45 }

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。