polymorphism doubt

[madhu7sudan]

Here is the code

using System;
namespace Polymorphism
{
class A
{
public void Foo() { Console.WriteLine("A::Foo()"); }
}

class B : A
{
public void Foo() { Console.WriteLine("B::Foo()"); }
}

class Test
{
static void Main(string[] args)
{
A a;
B b;

a = new A();
b = new B();
a.Foo(); // output --> "A::Foo()"
b.Foo(); // output --> "B::Foo()"

a = new B();
a.Foo(); // output --> "A::Foo()"
}
}
}


and My doubt is

for the class A instance is created as
A a:
a=new A( )

and in the last line
a= new B( )
is this possible

a is the instance of Class A. then how can it take the Class B

[gpraghuram]

Here is the code

using System;
namespace Polymorphism
{
class A
{
public void Foo() { Console.WriteLine("A::Foo()"); }
}

class B : A
{
public void Foo() { Console.WriteLine("B::Foo()"); }
}

class Test
{
static void Main(string[] args)
{
A a;
B b;

a = new A();
b = new B();
a.Foo(); // output --> "A::Foo()"
b.Foo(); // output --> "B::Foo()"

a = new B();
a.Foo(); // output --> "A::Foo()"
}
}
}


and My doubt is

for the class A instance is created as
A a:
a=new A( )

and in the last line
a= new B( )
is this possible

a is the instance of Class A. then how can it take the Class B

NOTE:Please use code tags while posting the code.

Is this a C++ code?
Post the code in right group.

Raghuram

[JonLT]

you can't acces members of B from A, it's the other way around:

A* a = new B();