It is astoundingly fast — hundreds of thousands of lines of code per minute (about ten times faster than other compilers), and it generates better quality code than the Sun compiler, and it generates better error messages. It is written in C++ which means it is not quite as portable as if it had been written in Java, but it is available for Window/Linux/AIX/OS2 etc. You can download it free. There is also a Jikes debugging package written in pure Java which runs anywhere, written by a different team. The easiest way to use Jikes on Win9x/NT is to download smartJC which converts Jikes into a semi-permanently resident DLL for even more speed. Jikes error messages are superb. They give you much better clues what the real problem is. You might not even need my list of error message translations. If Jikes dies with a addressing error, just delete all the class files and recompile. This seems to clear it. That was a problem with the previous version. I have not had enough experience with the new version to know if they have nailed it yet.

IBM provides no install instructions embedded in the download. Ignore any Jikes.1 file. It is a Unix MAN file. Just download the ZIP file, and extract jikes.exe to a directory on your path. Unlike javac.exe, jikes.exe wants rt.jar standard classes the classpath. This is explained in the FAQ. For Windows use you need the environment variables like this:

SET JIKESPATH=.;C:\;C:\Program Files\Java\j2re1.4.2_04\lib\rt.jar;
SET EXTDIRS=J:\Program Files\java\jdk1.6.0_06\jre\lib\ext