Java Reflection

Its a mechanism that enables dynamic discovery & binding of classes, methods, fields & all ther elements. Reflection can do more than just simply list of classes, fields & methods. Through reflection, we can actually create instances, invoke methods & access fields.

Reflection allows us to examine the object at hand and act accordingly during runtime. 

more... http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html