Hello Java, again.

I foolishly thought that I couldn't learn anything from Java, but I can
(and should, probably). In this place I'll play a bit with java and see
if I can learn a few new things about it.
Use correct consistent name for the java package.

 It's `lp.$language` as with the already existing ones.
Add a tested sliding window.

It provides a container that collects values with timestamps and
lets you access only the values in a certain "time window".
Extract adding/removing old/new values into methods.