What components of the JDK software have been open sourced?
In November 2006, Sun open sourced the Java programming language compiler (“javac”), and the Java HotSpot virtual machine. In addition, Sun open sourced the JavaHelp 2.0 extensible help system, Sun’s reference implementation of JSR 97. At JavaOne 2007, Sun open sourced most of the remaining components of the JDK, with the exception of a few encumbered components.