A minor variant on the skeletal implementation is the simple implementation, exemplified by AbstractMap.SimpleEntry. A simple implementation is like a skeletal implementation in that it implements an interface and is designed for inheritance, but it differs in that it isn’t abstract: it is the simplest possible working implementation. You can use it as it stands or subclass it as circumstances warrant.
And then discourage but don’t disallow subclassing? Doesn’t that go against earlier dictum? :)
