Javeleon is a small tool that enables developers to dynamically and transparently update actively running Java code within NetBeans modules in a test-instance of an application under development. A Javeleon module update ensures preservation of all of the current application state. It permits full Java class redefinition at runtime meaning that you can now change the inheritance hierarchy of classes at runtime and immediately use those changed types for already existing objects in the updated application.
For further details please refer to the following:
Note: In addition to the currently build-in support in NetBeans 6.9.1 for Ant-based NetBeans Platform development, Javeleon will soon provide out-of-the-box support for Maven-based NetBeans Platform development, starting from NetBeans 7.0 Beta, which is just around the corner.