Open up the JavaDoc and look for the word "Abstract" in the class names. Hey, it's at the top! Open one up and look for subclasses. These are some solid examples of how Sun did just what you're looking for.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi