Looking at String documentation takes a few seconds. If the developer can't look at the documentation in the interview, the developer is not the problem.
This comment applies to more of my real-life interviews than any other.
So many ask, "How do you do X?" and the correct answer in a real job situation is always either "Look up the documentation for X, and do it that way.", or "There is a 20-year-old open-source library for doing X, so I'd use that."
I am not a walking catalog of esoteric programming knowledge. When working, I have 24-hour access to all official documentation, as well as all blogs, projects, and message boards on the Internet. The first step in solving any problem is checking to see if someone else already solved it.
The same goes for the brain teasers. If you can look up the problem on the Internet, I probably saw it first. Your original, non-plagiarized riddles, please, or don't bring it in to the interview.