It’s good to see Sun getting into the spirit of openness in the ways that really matter – weekly builds of the J2SE Mustang release will be available from now, including the source code (source Mark Reinhold).  I’m not sure exactly what’s in the source code drops yet but even if the native code side of things isn’t included it’s still extremely useful.  Most if not all of the people interested in fixing bugs in a Java release are Java programmers so they’re most likely to be submitting patches on the Java side of things anyway.

The license isn’t an OSI approved license but personally I’d say that’s a good thing.  You can use the code in an academic setting and distribute it all you like for academic only purposes.  If you ever put it into production in any way shape or form it has to meet the compatibility tests.  Admittedly that still doesn’t allow for opensource projects to use the code nor does it solve the problems opensource projects have in getting access to the JCK but it does solve all the most pressing problems for Java programmers who need to make sure each release of the JRE will work for them and make sure their most critical bugs get fixed.  With this new process those that are willing to put in the time can ensure that their bugs are discovered early and fixed quickly.  That’s the big advantage of opensource.