Checkstyle is a development tool to help programmers write Java code that adheres to a coding standard. By default it supports the Google Java Style Guide and Sun Code Conventions, but is highly configurable. It can be invoked with an ANT task and a command line program.
some useful sources that should not stay in main repo but it is good to host them
The Eclipse Checkstyle plug-in integrates the Checkstyle Java code auditor into the Eclipse IDE. The plug-in provides real-time feedback to the user about violations of rules that check for coding style and possible error prone code constructs.
Support on Checkstyle in SonarQube. Officially transfered from http://www.oddjack.com/?certs=SonarQubeCommunity/sonar-checkstyle