I have been working on packaging some of my (mostly) research code into four libraries (a picture), three that depend on a forth.

My concern is mostly “Java IDE kung-fu”: users of these libraries (mostly just me only want the highest level APIs to show in popup completion lists and the entire set of implementation classes remain invisible. The solution is easy: a public API class with implementation classes in the same package with package-ony (i.e., neither public or private) visibility.