If you are interested in this thread, you may want to check out the
CollectionUtils class I just added. It provides several set theoretic
operations for generic Collections. It could be optimized for specific
Collection implementations, but it implements what seemed to me to be both
intuitive and rigorous.
The semantics here aren't quite the same as they are for ListUtils though.
Do we want to keep ListUtils, deprecate it, or just drop it entirely?
(Frankly I think ListUtils is a bit counter-intuitive in its behavior, so I
lean toward dropping it, but whatever you guys think...)
