I've finally gotten everything to do what it needs to do.
My original posting related only to part 6 of an 8 part problem (which I haven't finished yet), but part 6 is definitely the "core" of the exercise. I've posted all the code for the class below - there are some methods in it which we haven't really discussed here which were required by earlier parts of the exercise. I don't think my code is beautiful and almost certainly it is not elegant, but it does demonstrate that a bull in a china shop might eventually achieve a good end. Based on the messages I've gotten from NetBeans, there seem to be plenty of opportunities to use functional expressions to save some typing, but I've made the decision not to use those until I have a more solid grounding on the "old style" code. Lord knows I need it.
The discussions on this thread have been fascinating, enlightening and helpful. Thanks to everyone. I can't say I used anyone's code entirely, but I'm pretty sure I've stolen a piece here or there from almost everyone who posted.
If there's interest, I could write the MOOC organizers and ask for permission to upload the entire exercise. They're revamping the course anyway over the next few months, so they might not mind. Piet Souris, in particular, mentioned that he considered this an excellent exercise. I know it sure as hell taught me a lot, but I'm old enough that my ego can handle the beating. And it took a real beating... Anyway, here's the code. There are a lot of stupid/trivial comments, but I found it necessary to use them to keep my mind from exploding. I've also included (again - sorry for the repetition) the instructions provided by the devious bastards that designed the course. The instructions are after the code.
Create the class FilmComparator in the package reference.comparator. The class FilmComparator has to implement the interface Comparator<Film>, and it has to have the constructor public FilmComparator(Map<Film, List<Rating>> ratings). The class FilmComparator will be used later on to sort films according to their ratings.
The class FilmComparator has to allow for film sorting according to the average of the rating values they have received. The films with the greatest average should be placed first, and the ones with the smallest average should be the last.
Thanks again everyone. I'm gonna have a glass of bourbon and go to bed. More code in the morning!