base class extended object implamentation

Question

Bit of a noobie question but hey ho.

Example:

BaseClass bc = new ExtendedClass(); //Assume ExtendedClass inherits from BaseClass
((BaseClass)bc).ExtendedMethod();
bc.ExtendedMethod();
((ExtendedClass)bc).ExtendedMethod(); //overridden in ExtendedClass

ExtendedClass ec = new ExtendedClass();
((BaseClass)ec).ExtendedMethod();
ec.ExtendedMethod();
((ExtendedClass)ec).ExtendedMethod(); //overridden in ExtendedClass

?

What implementations will bc.ExtendedMethod(); and ec.ExtendedMethod(); call at runtime? Will they be different? I assume the casted calls will call the specific implementation within the class.

edit: added relevant tag.

Why don't you give it a shot yourself, setup a sample project with base and child class and see — Habib, Apr 05 '13 at 10:18
It's just with methods that only appear within the extension require a cast to be usable from the extended base class object and I was actually seeing if I could snag the actual concept of this *ty alex* and actually have this somewhere useful so that every programmer doesn't have to test this to find out. — Izzy, Apr 05 '13 at 10:31

score 2 · Answer 1 · answered Apr 05 '13 at 10:20

2

In all three cases the overridden implementation of ExtendedMethod will be called, as you are creating an instance of ExtendedClass. After all, this is what polymorphism is all about.

answered Apr 05 '13 at 10:20

Alexander Tsvetkov

1,649
14
24

score 2 · Accepted Answer · answered Apr 05 '13 at 10:31

public class Base
{
    public void Extends()
    {
        Console.WriteLine("Base class");
    }
}

public class Extend : Base
{
    public new void Extends()
    {
        Console.WriteLine("Extend class");
    }
}


public class Program
{
    public static void Main()
    {

        Base b = new Base();
        b.Extends();

        Extend e = new Extend();
        e.Extends();

        Base be = new Extend();
        be.Extends();

        Console.Read();

   }

}

Results in the following output:

Base class
Extend class
Base class

Note you can also use the new keyword in the Extend class to hide the base Extends function.

public new void Extends() 
{

}

Ahh ok - if you use virtual+override the last one is Extended; but if you use "new" the last is Base. — Izzy, Apr 05 '13 at 10:42

base class extended object implamentation

2 Answers2