C#父类引用指向子类

    今天研究了一下 C#中有关父类引用指向子类的问题。所谓“父类引用指向子类”是指声明为父类对象，但实例化创建子类对象。举例说明父类Teacher、子类Professor，声明和实例化：Teacher liming = new Professor (); 将liming声明为教师类，但实例化成教授。先看一段代码：

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

namespace ConsoleApplication3
{
class A
{
public virtual void print()
{
Console.WriteLine ( "A::print()" );
}
}
class B : A
{
public override  void print()
{
Console.WriteLine("B::print()");
}
}

class C :  B
{
public void print(A a)
{
a.print();
}

public override void print()
{
Console.WriteLine("C::print()");
}
static void Main(string[] args)
{
A a = new A ();
A pa = new A ();
A pb = new B ();
A pc = new C ();
B b = new B ();
C c = new C ();
a.print ();
b.print();
c.print ();
pa.print();
pb.print();
pc.print();
c.print(a);
c.print(b);
c.print(c);
String str1 = pa.GetType().ToString();
String str2 = pb.GetType().ToString();
String str3 = pc.GetType().ToString();
Console.WriteLine(str1);
Console.WriteLine(str2);
Console.WriteLine(str3);
Console.ReadKey();

}
}
}

 输出结果如下：