Is a standalone abstract class of any use ?

[Jayati Das]

I was asked this in an interview recently , If an abstract class is not going to be extended ,does declaring a class abstract serve any purpose ?
I couldnt think of any use of a standalone abstract class.

[Ralph Cook]

I suppose you could still call static methods on such a class, but I'd hardly call that a reason for having an abstract class that isn't extended. Sounds like one of those nice 'trivia' 'gotcha' questions some interviewers like.

[Jayati Das]

Thank you for replying.

[Winston Gutkowski]

Jayati Das wrote:If an abstract class is not going to be extended ,does declaring a class abstract serve any purpose?

I think my answer would be 'no', because the whole point of an abstract class is to be extended, so the idea of a 'standalone' abstract class is a bit of an oxymoron.

The only example that I can think of would be a constants-only interface, and those have generally been discredited.

However, I totally agree with Ralph: I think it's one of those 'gotcha' questions; and not very well worded at that.

Winston

[Matthew Brown]

I suspect they're thinking of a Utility - i.e. a class that only has static methods. For example, java.lang.Math.

[Campbell Ritchie]

Utility classes are not usualloy abstract. They are usually unintantiable.

[Matthew Brown]

Campbell Ritchie wrote:Utility classes are not usualloy abstract. They are usually unintantiable.

I know. I still reckon that's probably what they were getting at, though .

Or, having thought a bit more about it, maybe they were looking for the answer "no - if you want an uninstantiable class you should do it a different way" (i.e. the way mentioned in that link).