We want you to contribute to the Mac OS X Port of OpenJDK!
There are only a few things you need to do:
0. Sign the Oracle Contributor Agreement
1. Join the mailing list
2. Have fun hacking!
We have a few resources to help you get started with Cocoa and AppKit if you aren't already familiar with them.
We also have a few pages about how we develop Java on Mac OS X
Overview
Content Tools
ThemeBuilder