My Activity Monitor shows a "java" process taking up 400 MB RAM.
sudo jps show only
JPS. How do I find out what's running java?
In System Monitor select the process, go to the "i" icon and press it.
It should appear a new window with some informations, see process group.
If you could not understand what's going on, go to "Open files and ports" and you should see all the files, try to reach what application is using it and the job is done!