I just came across this post which talks about a Java to Python converter that the author wrote and posted on Google code. It uses a Java 1.5 JJTree grammar and a Visitor that gets callbacks for pretty much all the AST nodes.
One nice thing that it does is print some type documentation for parameterized types, e.g.:
Rather a clever idea.
The PMD jar file is in the project's lib directory, but it looks like the author ended up going with a different Java 1.5 grammar. That's understandable since the PMD grammar is full of all sorts of PMD-specific things like
NOPMD lexical states and whatnot. Anyhow, seems like a nifty project!
My JavaCC/JJTree book is coming down the home stretch now... should have something in print in the next few months. w00t!