Note that development on this compiler has long ceased, although the compiler and documentation are still available. IBM's Jikes Java Compiler Jikes is IBM's Java compiler that is supposedly faster than most other compilers. It is also able to compute the dependency requirements in programs and so generate makefiles. If you want faster development cycles, you might also fancy its ability to perform incremental compilations. The compiler handles constructs exactly according to the Java specifications.
Source code appears to be provided.
You can get free Java Development Kits for a number of platforms from the creator of Java. The kits include the compiler, debugger and libraries for generating Java bytecode. I find this compiler rather slow. This Java compiler is developed independently of the one by Sun. It is able to generate both Java bytecode and native machine code .