Checkstyle is a development tool to help programmers write Java code
that adheres to a coding standard. It automates the process of
checking Java code to spare humans of this boring (but important)
task. This makes it ideal for projects that want to enforce a coding
standard.

Checkstyle can be used as either a commandline utility or as an
Ant task.

WWW: http://checkstyle.sourceforge.net/