I don't have to imagine; I've received, "What is an interface?" as a first question in three different interviews over the last couple of months. Never mind that Java isn't anywhere on my resume, I made it clear to the recruiter before the interview that I don't know Java (not that I mind learning if necessary for the job, just don't send me to a job interview that requires it), and they were ostensibly interviewing me for a senior non-Java-specific position that required solid math skills.

I'm not quite sure what they're trying to filter for, but when one uses language-specific trivia as a starting point for an interview, it's going to filter out a lot of people that many companies claim they're so desperate to hire.