Method parameter can be a class or interface, little confused

Question

Hi,

If I have a class:

public blah
{

}

Then I have another class that inherits blah"

public ablah : blah
{

}

Can I do this then?

public class Someservice
{
 public bool SomeBlah(blah b)
 {

 }   
}

Could I call it the service with either classes blah or ablah?

ie.

Someservice s1 = new Somesercie();

s1.SomeBlah(new blah());

s1.SomeBlah(new ablah());

I saw this somewhere, and I thought this was only possible if one used an Interface?

Answer 1

That would work just fine. (assuming that it would compile... check your spelling)

Answer 2

It's called polymorphism and it's possible with classes as well as interfaces.

Generally you would use a class if you wanted to provide some of the implementation in the base class (which is not possible inside an interface declaration). Also interfaces only allow for public members..

Answer 3

You can do this just fine. You're using standard inheritance, in this case. The best way to think of it is this: "ablah" is a "blah", so you can use an "ablah" instance anywhere that's expecting a blah.

A common example is a

public class Animal {} 
public class Dog  : Animal {}

In this case, "Dog" is an "Animal" (which you'd expect), so if you have a method that takes an animal, it will work with a Dog.

Answer 4

Yep, although it is not using an interface but rather a facet of object oriented programming called Polymorphism (http://msdn.microsoft.com/en-us/library/ms173152(VS.80).aspx)

If you had

public class Someservice{ 
    public bool SomeBlah(ablah b) 
    { }  
}

Your SomeService code wouldn't work, because while you can cast an ablah object into a blah object, you cannot do the reverse. It's like saying I have a car (blah), and it's a Toyota (ablah). If I was doing something that needed a car, my Toyota would fit the requirement. But if I was going to do something that required a Toyota, I couldn't use any old car.

HTH. pk