How Best to Compare Two Collections in Java and Act on Them?

Question

I have two collections of the same object, Collection oldSet and Collection newSet. The required logic is as follow:

Answer 1

Apache's commons.collections library has a CollectionUtils class that provides easy-to-use methods for Collection manipulation/checking, such as intersection, difference, and union.

The org.apache.commons.collections.CollectionUtils API docs are here.