Eclipse Checkstyle Plugin

The plugin uses a project builder to check your project files with Checkstyle. Assuming the Eclipse Auto-Build feature is enabled each modification of a project file will immediately get checked by Checkstyle on file save - giving you immediate feedback about the changes you made. To use a simple analogy, the Checkstyle Plug-in works very much like a compiler but instead of producing .class files it produces warnings where your code violates the Checkstyle rules. The discovered deviations are accessible in the Eclipse Problems View, as code editor annotations and via additional Checkstyle violations views.
Learn here how to activate Checkstyle for a project.

The set of rules used to check your code is highly configurable. A Checkstyle configuration specifies which check rules are validated against your code and with which severity violations will be reported. Once defined a Checkstyle configuration can be used across multiple projects. The plugin comes with several pre-defined Checkstyle configurations.
You can create custom configurations using the plugin's Checkstyle configuration editor or even use an existing Checkstyle configuration file from an external location.
A short introduction into creating your own Checkstyle configurations can be found here.