Java's XSLT transformer does that by default -- it compiles XSLT into
Java byte-code, called translet. I don't know how to use it
separately, though.
AFAIK Micheal Kay from Saxonica and at least several other projects
are working on that as well.

A friend asked me if there is something like a cross-compiler which converts a XSLT stylesheet into a java (source) programm.

His boss forces him to write java programs to process XML documents.
Of cause - with XSLT this is much more comfortable. So the best way for him would be to
write internally XSLT stylesheet which performs the task and convert them
officially into a java program.

Is there a way to do this ?
No XSLT processor like Saxon should be necessary to run the java program later.

Ben