polymorphism and abstract classes

elvisfeverr · #1 (**permalink**) February 3rd, 2008, 04:42 PM

I could not understand why to use a pure virtual function to make the class an abstract class insted of using only a virtual function.Or even why to use a virtual function and define a pointer to base class that points the derived class we could use a pointer of type derived class itself instead they say that is called polymorphism.Can someone please tell me advantages of using them by giving some practical examples.Thank you.

Peter_APIIT · #2 (**permalink**) February 20th, 2008, 04:16 AM

I could not understand why to use a pure virtual function to make the class an abstract class instead of using only a virtual function

As far as i know, a class ia abstract when contain one pure virtual function.

The purpose of pure virtual function is this function may redefined my your later derived class function.

It seems unpractical for me because i also cannot see this usage of this features because this is out of my knowledge.

Polymorphism is the most difficult part of OOP.

http://en.wikipedia.org/wiki/Polymor...ed_programming

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lacos · #3 (**permalink**) February 21st, 2008, 06:20 AM

hi, maybe this simple example can help

Quote:

quote:
class Object
{
public:
    virtual void draw()=0;
};

class Car: public Object
{
public:
    virtual void draw()
    {
        //car specific drawing
    };
};

class Airplane: public Object
{
public:
    virtual void draw()
    {
        //Airplane specific drawing
    };
};

...

class Graphics
{
public:
    void DrawObjects(Object* pObject)
    {
        pObject->draw(); //can handle draw for every derived class from object
    }
};

...

victor2008 · #4 (**permalink**) October 16th, 2008, 01:39 AM

Polymorphisms is a single variable is used with several different types of related objects at different places in a program and Abstract is a class which cannot be instantiated.
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Victor
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