One of my favorite features in Python (I know it's not really a feature of python) is doc-testing. For me it really augments standard documentation and helps to keep it up to data. Looking for something similar in Java, I've found JDocTest - http://cscott.net/Projects/JDoctest/ - last updated two years ago, and doctestj http://code.google.com/p/doctestj/ which haven't been updated since 2007.
Obviously, Java is not interpreter based like Python, but maybe there's some up to date library that enables doctest like capability in java?