What I stated was because you insist to contribute the Persian calendar  based on java.util.Calendar and yes you may create your own source codes and nobody would complains. Although this is already implemented as the other friends told you and you can find it on sourceforge website.

And, yes, JDK is under the open source license, namely OpenJDK. you can go through following links but still you can't contribute and get involved in their open source projects.

http://www.sun.com/software/opensource/java/
http://openjdk.java.net/
http://openjdk.java.net/projects/jdk6

And for your information you can't browse the projects in above links because you access it from a sanctioned country! you have to go with a proxy software or an Anti-filter