I think this question is really stupid without knowing the context. Did he talk about a particular kind of objects? And what should "buffered" mean exactly? In my opinion without more information this question is pointless.
I think, a PhD should be able to ask smarter questions. And if he meant "heap" but asked about "buffer" he can't expect someone other to give a good answer for a wrong question ;-)
OK, now we have "buffer", "heap", "string literal pool" and "cache"... What else?
Of course there are concepts like cache or buffer all over the JDK but in my opinion the question is still stupid. In Java there's no generic concept like an "object buffer" and that's the point here!
Surely your answers would've been great if that PhD had asked for examples of a cache or object pool in the JDK.