How much of a red flag is it if a programmer gets concepts like interfaces and classes, but when asked what an interface is, can't give me a straight answer?

Some coders require a language context for their brain to work. Try asking what an interface does in a specific language known by the coder.

It might just be someone who doesn't have experience explaining those concepts to others.

Classes and interfaces are abstract concepts and not everyone who understands them also memorized the bullshit bingo text. Give them code to look at so they know what you're even asking.

The fact OOP today is basically the "we have OOP at home" version of what it's supposed to be while some people (like educators) pretend otherwise doesn't make things easier.

I don't see it as a big deal, as long as he can actually use interfaces.

An interface is a contract, only provides definition of method's, can be extended multiple times (depending on language).

Did you expect an answer like that?

@IntrusionCM an answer like that would have been more than enough. Just some recollection of it being like a layout for implementing classes.

Thanks for the input! I was on the fence on this one but I'm glad to see a solid leaning to one side.

@atlas1515 the thing is... It's a stressful situation.

I can deal with burning buildings, arsehole clients, ....

... But I absolutely hate being tested. Hate is the wrong word, I have a very strong fear of exams.... And a job interview is nothing else.

Don't judge too quickly. Many feel like sitting on an electric chair during an interview - and blank out completely on stuff they deal with on a daily basis.

I think the interviewer should ask “How and why do you use an interface?” The explanation would be more practical instead of an expected cliché answer such as “It is a contract”. Dictionary definitions are like memorising multiple choice questions. When it is asked that way it gives the impression that you should give a theoretical answer. That doesn’t work for me personally and I lose my enthusiasm in the interview and for the role. However I would be very happy to talk about interface segregation and the good practices etc