In the past, Java was just a language with a proprietary compiler. That is, you couldn't say you had a Java compiler unless you met the restrictions set by Sun Microsystems.
That had the FOSS (Free Open Source Software) community at odds. Here was Java, a great object-oriented language that was platform independent. A program written in Java would work on any computer that had a Java interpreter. But the compiler was proprietary. Although it was free (as in beer), it was not free (as in freedom). FOSS people were concerned that Sun might one day change the terms of their licensing and could charge for it. All that Open Source Software written in Java would now be hamstrung by the proprietary compiler and runtime environment required to run it.
According to an article on Slashdot
, Sun has moved Java to the GPL (GNU General Public License) making the most of the source code for binaries available to developers.