If you've ever gotten a ClassCastException and just knew the runtime was wrong about it, or found yourself copying .jar files all over your production server just to get your code to run, then you probably find the Java ClassLoader mechanism to be deep, dark, mysterious, and incomprehensible. Take a deep breath, and relax--ClassLoaders aren't as bad as they seem at first, once you understand a few basic rules regarding their operation, and have a bit more tools in your belt to diagnose ClassLoader problems. And once you've got that, and hear about ClassLoaders' ability to run multiple versions of the same code at the same time, and to provide isolation barriers inside your application, or even compile code on the fly from source form, you might just find that you like ClassLoaders after all... maybe.

For a beginning to intermediate Java audience.