GNU Compiler for Java

The GNU Compiler for Java (GCJ) is a free software compiler for the Java programming language that is part of the GNU Compiler Collection. It can compile Java source code to either Java Virtual Machine bytecode, or directly to machine code for any of a number of CPU architectures. It can also compile class files containing bytecode or entire JARs containing such files into machine code. Almost all of the runtime libraries used by GCJ come from the GNU Classpath project.

http://gcc.gnu.org/java/