This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
You are assuming that all the objects have an equals method defined? (this assumption is ok, I just want to state it.) You may run into trouble if the collections contain duplicates. For example if collection a is [X,X,Y] and collection b is [X,Y,Y], your code will not catch the difference. If the collections can't contain duplicates, the second check for containsAll is redundant.