You can use BeanShell interactively for Java experimentation and debugging as well as to extend your applications in new ways. Scripting Java lends itself to a wide variety of applications including rapid prototyping, user scripting extension, rules engines, configuration, testing, dynamic deployment, embedded systems, and even Java education.
BeanShell is small and embeddable, so you can call BeanShell from your Java applications to execute Java code dynamically at run-time or to provide extensibility in your applications. Alternatively, you can use standalone BeanShell scripts to manipulate Java applications; working with Java objects and APIs dynamically. Since BeanShell is written in Java and runs in the same VM as your application, you can freely pass references to "live" objects into scripts and return them as results.
In short, BeanShell is dynamically interpreted Java, plus a scripting language and flexible environment all rolled into one clean package.URL: http://www.beanshell.org