A base class reference can refer to a derived class object : Derived Class : Class C# Examples

    
using  System;  
  
class  BaseClass  {  
    public  int  a;  
  
    public  BaseClass(int  i)  {  
        a  =  i;  
    }  
}  
  
class  DerivedClass  :  BaseClass  {  
    public  int  b;  
  
    public  DerivedClass(int  i,  int  j)  :  base(j)  {  
        b  =  i;  
    }  
}  
  
class  MainClass  {  
    public  static  void  Main()  {  
        BaseClass  x  =  new  BaseClass(10);  
        BaseClass  x2;    
        DerivedClass  y  =  new  DerivedClass(5,  6);  
  
        x2  =  x;  //  OK,  both  of  same  type  
        Console.WriteLine("x2.a:  "  +  x2.a);  
  
        x2  =  y;  //  Ok  because  DerivedClass  is  derived  from  BaseClass  
        Console.WriteLine("x2.a:  "  +  x2.a);  
  
        //  BaseClass  references  know  only  about  BaseClass  members  
        x2.a  =  19;  //  OK  
//        x2.b  =  27;  //  Error,  BaseClass  doesn't  have  a  b  member  
    }  
}