on my exam there were 5 util questions. it is definately worth remembering what these words mean: Tree -- ordered Sorted -- err.. sorted! Set -- no duplicates. Hash -- errr.. can't remember -- anybody? Map -- have a key (have a mapping) as most of my questions were based around: if you want to create a collection with these features which of the following would you use... it is also remembering important methods such as put and add and where they are appropriate also note where null can be used and where it cannot be used.