I installed the Eclipse plugin for FindBugs without any problems.
I ran it and got about 80 warnings/errors.
It found one more place where I needed .equals - I'd missed it because I didn't think to look for != as well as == (oops!)
It found a bunch of places where I had compareTo without equals or equals without hashCode.
I fixed about half. The remainder are either minor or can wait. Ideally I'd like to clean them all up so I don't have to keep looking for real problems among the ones I'm ignoring.
The minimal effort to install and run FindBugs was definitely worth it.
Then I moved on to a test failure where jSuneido is optimizing a query slightly differently than cSuneido. Both ways work and there isn't an obvious "better" way. I could just ignore it. But in theory they're running the same algorithm so they should be coming up with the same answer. In my experience these kinds of anomolies usually lead to actual problems. (Where there's smoke there's fire.)
Along the way I have found a few minor bugs, even a couple that also exist in cSuneido. But so far I can't figure out why the difference in behavior. It's frustrating but I'll get it eventually.