Thread created to share small, library independent (except OpenGL bindings) hints and tips. Please do not post obvious ones, let this topic become a valuable source of informations. 
I will start with this one:
Did you know that you can use WeakReference objects to allow garbage collection of objects which are no longer accessible via “classic” references? In case of games, this can be useful for example in case of listeners.
More info/explanation: http://java.dzone.com/articles/reference-types-java-part-1