OpenJDK is the effort by Sun Microsystems to release a fully buildable Java Development Kit based completely on free and open source code.

Sun's promise and initial release

Sun announced in JavaOne 2006 that Java would become open source software,

Sun released the Java HotSpot virtual machine and compiler as free software under the GNU General Public License on 13 November 2006, with a promise that the rest of the JDK (which includes the JRE) would be placed under the GPL by March 2007 ("except for a few components that Sun does not have the right to publish in source form under the GPL"). According to Richard Stallman, this would mean an end to the Java trap. Mark Shuttleworth called the initial press announcement, "A real milestone for the free software community".

Release of the class library

Following their promise to release a fully buildable JDK based almost completely on free and open source code in the first half of 2007 1, Sun released the complete source code of the Class library under GPL on May 8, 2007, except some limited parts that were licensed by Sun from 3rd parties who did not want their code to be released under a free and open-source license. Included in the list of encumbered parts were several major components of the Java GUI system. Sun stated that their goal was to replace the parts that remain proprietary and closed source with alternative implementations and make the class library completely open.

Community improvements

On 2007-11-05, Red Hat announced an agreement with Sun Microsystems, signing Sun's broad contributor agreement (that covers participation in all Sun-led free and open source software projects by all Red Hat engineers) and Sun's OpenJDK Community TCK License Agreement (That gives the company access to the test suite that determines whether a project based on openJDK complies with the Java SE 6 specification).

Also on November 2007, the porters group was created on OpenJDK to aid in efforts to port OpenJDK to different CPU architectures and operating systems. The BSD porting projects2, led by Kurt Miller and Greg Lewis and the Mac OS X porting project (based on the BSD one) SoyLatte led by Landon Fuller3 have expressed interest in joining OpenJDK via the porters group and as of January 2008 are part of the mailing list discussions. Another project pending formalization on the porters group is the Haiku Java Team, led by Bryan Varner .

On December 2007, Sun moved the revision control of OpenJDK from TeamWare to Mercurial, as part of the process of releasing it to open source communities.

OpenJDK has comparatively very strict procedure of accepting code contributions: every proposed contribution must be reviewed by two of Sun's engineers and have the automatic test demonstrating that feature has been fixed. This ensures the persistent high quality of the code but also means that even a trivial fix may take many weeks to approve. However, although initially the fixes proposed by the community were committed by Sun in the codebase, September 2008 saw the first (significant) patches directly committed by a non-Sun or ex-Sun employee.