Annotations were added to the Java programming language in release 5.0 and were rapidly adopted as a means for building tools of all sorts.  For this reason, annotations are usually defined and processed by tool providers (such as Junit, EJB 3, etc.).  While Java developers use pre-defined "tool" annotation, they rarely ever define and process annotations of their own.  However, definition and processing of annotations is fairly easy, especially since Java 6.0, where the Java compiler support annotation processing on the source code level by means of compiler plug-ins.  Knowledge of annotation processing enables developers to build utilities of their own.

This tutorial aims to provide a brief overview of annotations (their definition and usage) and of annotation processing at runtime via reflection and on the source code level via compiler plug-ins.  Using a case study we will illustrate the implementation of a compiler-plugin for processing annotations in the source code.