Enterprise Architect for the Windows Platform allows java/c++ code
generation from the CASE tool.

http://www.sparxsystems.com.au/

A popular open source uml  CASE tool  is argoUML. This is written in
Java and is available from

http://www.argouml.org/

There have also been a number of spin-offs from argoUML I beleive.
You could try and search sourceforge.net for UML or CASE tools  and see
what you find.