Inheritance and interfaces .NET

Question

Quirky question:

Imagine that I have a base class called BaseFoo. I have an interface with some methods called IFoo. And I have tons of classes beneath BaseFoo.

If i implement the interface in BaseFoo, i dont need to implement in the inherited classes, correct?

Ok, but imagine that i have a generic function that will treat IFoo's. Do i need to explicitely declare that they implement IFoo?

Like this (pseudo-illustrational-code)

public class BaseFoo:IFoo;

public interface IFoo;

Should i do this?

public class AmbarFoo:BaseFoo,IFoo

or?

public class AmbarFoo:BaseFoo

What is the most correct way? Are the effects the same? If i test if AmbarFoo is a IFoo what will I get?

Thanks

Jon Skeet · Accepted Answer · 2010-01-15 16:07:23Z

7

It will behave the same way regardless. You'd only need to restate the interface name if you wanted to reimplement the interface with explicit interface implementation. An instance of AmbarFoo will indeed "say" that it implements IFoo.

answered Jan 15, 2010 at 16:07

Jon Skeet

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3 Comments

Joooohn Over a year ago

Thanks! Exactly the answer i needed.

Hamish Grubijan Over a year ago

I think Jon Skeet should skip questions like this one.

Jon Skeet Over a year ago

@Gordon: You're aware of the Jon Skeet Facts question on Meta, right? meta.stackexchange.com/questions/9134/jon-skeet-facts

Dave Sims · Accepted Answer · 2010-01-15 16:11:06Z

0

If i implement the interface in BaseFoo, i dont need to implement in the inherited classes, correct?

No, because BaseFoo will be forced to implement, and the child classes will inherit the implementation. They will all still be IFoos though.

answered Jan 15, 2010 at 16:11

Dave Sims

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Comments

Matthias · Accepted Answer · 2010-01-15 16:11:38Z

0

In your case it won't change anything.

However, look at the following one:

public interface IFoo
{
    void Bar();
}

public class FooBase
    : IFoo
{
    public void Bar()
    {
        Console.WriteLine("FooBase");
    }
}

public sealed class SubFoo
    : FooBase//, IFoo
{
    public new void Bar()
    {
        Console.WriteLine("SubFoo");
    }
}

Now run the following and comment out the "//, IFoo".

SubFoo foo = new SubFoo();

foo.Bar();
((IFoo) foo).Bar();

However, this is more theoretically.

Leave it away.

answered Jan 15, 2010 at 16:11

Matthias

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