how to contribute in openSource Java application

A good tutorial for beginners who want to contribute in open Source project (written in java),
the tutorial shows a step by step to checkin/checkout (read/write) existing openSource projects in java.net,
using the Eclipse cvs tool (concurrent versioning system) :

https://eclipse-tutorial.dev.java.net/eclipse-tutorial/part1.html

and don't forget to visit part 2 of the tutorial