What are virtual functions ?

[sandeep kokane]

What are virtual functions ? and Can we call Virtual funciton in a constructor ?

[Wilfried LAURENT]

This is a Java(TM) forum, not a C++ forum.
You may want to talk of interfaces...
W.

[Ilja Preuss]

In short, "virtual function" is the C++ term for a polymorphic function/method.
In Java, all (non-static) methods are polymorphic - there is no way to declare a "non-virtual function".
[ July 11, 2002: Message edited by: Ilja Preuss ]

[Frank Carver]

Sorry Ilja, but declaring a method as "final" in Java is roughly equivalent to a non-virtual in C++.
It's a horrible thing to do though.

[Jim Yingst]

Declaring a function "private" also makes it effectively non-virtual.

[Ilja Preuss]

Originally posted by Frank Carver:
Sorry Ilja, but declaring a method as "final" in Java is roughly equivalent to a non-virtual in C++.
It's a horrible thing to do though.

Yeah, *very* roughly...
Mhh, can you declare a method as non-virtual which overrides a virtual one in C++? What would happen?

[Ilja Preuss]

Originally posted by Jim Yingst:
Declaring a function "private" also makes it effectively non-virtual.

Yes, you are right, of course.

[Anthony Villanueva]

Hi sandeep,
The virtual modifier signals the compiler that this member function is expected to be overridden by a derived class. See the sample code below:

 
#include <iostream.h>
class Base
{
public:
virtual void getMessage();
};
class Derived: public Base
{
        public:
void getMessage();
};
int main()
{
Base* b1 = new Derived;
b1 ->getMessage();
Base* b2 = new Base;
b2 ->getMessage();
        return 0;
}
void Base::getMessage()
{
        cout << "Base" << endl;
}
void Derived::getMessage()
{
        cout << "Derived" << endl;
}

The member function invoked depends on the runtime type of the object being referenced by the pointer. Note this polymorphic behavior only applies to pointers and references.

[sandeep kokane]

Thanks A Lot all of u. Actually i know that there is not "virtual" keyword in the JAVA. But the question about is asked me in the JAVA technical interview. So i was confuse that time. Thanks A lot again .