Why is java always running?
Try typing this into terminal:

ps axv | grep java



This should output details about which jar file is open in the runtime. 


Alternatively, to find out which applications are using the Java Runtime select java in the activity monitor and clicking on the blue i icon. 

Click 'Open Files and Ports' and see if it gives you a clue which application launched the java environment. You'd be surprised which applications depend on Java! 




You could also try going into the Java System Preference, clicking the Java Tab and choosing View.... You'll see a list of registered Java applications that might help you find the culprit.