http://jgap.sourceforge.net/
WHAT IS JGAP?
JGAP (pronounced "jay-gap") is a Genetic Algorithms and Genetic Programming component provided as a Java framework. It provides basic genetic mechanisms that can be easily used to apply evolutionary principles to problem solutions. See the examples for a demonstration or watch out the graphical tree that can be created with JGAP for found solutions of genetically evolved programs.
JGAP was designed to be very easy to use "out of the box", while also designed to be highly modular so that more adventurous users can easily plug-in custom genetic operators and other sub-components.
Documentation, quality and stability of code are the top concerns when developing JGAP. You find really many unit tests packaged with JGAP, extensive Javadocs, and quite a lot of examples. Compare JGAP with other projects! Feedback is always welcome.