The Checkstyle team has made available a version 4.0 beta 1 available for use. You can get it from the download page. This release introduces preliminary support (beta quality) for the Java 5 language. Previous versions of Java are still supported so this release should be a drop in replacement for the 3.5 release.

The reason for the beta release is to solicit feedback on the Java 5 support, a lot of which was provided by Michael (thanks!).

Other new features and bug fixes are documented at here.