Hybrids Combine GNU Classpath and OpenJDK
The first GNU Classpath/Sun Java hybrids have begun to appear. The hybrids combine GNU Classpath with Java code that Sun has recently released under the GPL either to improve an existing project or to further the goal of having a completely Free JDK. First IKVM made a snapshot available, thus allowing parts of the OpenJDK class libraries to be used on Mono and .NET. Then the CACAO team released a new version that allows Sun's phoneME to be used as core libraries. Finally, Red Hat launched IcedTea to allow the OpenJDK to be built using only Free Software and to provide stubs and replacements from GNU Classpath for the remaining binary plugs in the OpenJDK.
IKVM.NET is an implementation of Java for Mono and the Microsoft .NET Framework. Previously it used the GNU Classpath implementations of the Java class libraries. It has now begun the "long journey" of integrating libraries from the OpenJDK. The first snapshot was released May 31 and another on June 13.
CACAO is a JITed JVM supporting the i386, x86_64, Alpha, PowerPC, ARM, MIPS, and MIPS32 architectures. CACAO uses GNU Classpath as its default Java core libraries. The 0.98 "Free all JITs!" release added support for using Sun's phoneME CLDC 1.1 classes as Java core libraries.
Sun has released almost all of the JDK under the GPL, with one of the key words being, "almost." There are still a number of "binary plugs," which represent encumbered components. Red Hat has launched the IcedTea project, with the goals of (1) allowing the OpenJDK to be built using only Free Software and (2) providing Free stubs and replacements for the binary plugs. As much as possible, the replacement code has been pulled from from GNU Classpath, but the IcedTea project has also created stubs for dependencies that can't be satisfied by GNU Classpath. IcedTea "is not intended to be a permanent project - just a stopgap measure" until the work can be incorporated directly into the OpenJDK.
It is encouraging that the code sharing is already going both ways. Free Software projects are not just incorporating the newly freed code, they are also helping to advance the OpenJDK. It seems clear that this is only the beginning.
Tom Gilb & Kai Gilb Jan 26, 2015