Checkstyle

Checkstyle is an open-source Java code-quality and static-analysis tool that checks source code against coding standards and configurable best-practice rules. It supports the Google Java Style Guide and Sun Code Conventions by default, and its checks can be configured in XML, including rules such as detecting fall-through between branches of a switch statement.

It can be run as a command-line program or an Apache Ant task, and can be added to builds through Maven Central. The project is developed and maintained by volunteers and is licensed under the GNU LGPL v2.1.