Unraveling Java class loaders

A few days ago I wrote about a singleton that was being created twice.
 I blamed it on different class loaders, but my colleagues 
 were skeptical. “That might fix it, but that's not the cause.”
 I was a little disappointed. I'd been rather proud of figuring it out on my own,
 and I was sure I was right. Still, I couldn't explain exactly why it behaved that way.

About a week later, the java.cz mailing list was discussing
 how files are deployed on a J2EE application server, so I took the opportunity 
 to ask. Martin Kuba (makub) explained that a class is uniquely identified 
 by its qualified name (package plus name) and the class loader that loaded it.
 I was glad to have been right, and I left it there.

Today I came across an excellent article on ONJava.com by Andreas Schaefer, 
 Inside Class Loaders,
 which cleared up practically everything about Java class loaders for me. I highly recommend it. This is the first part,
 and the next installment will cover class loaders in the context of J2EE application servers and AOP.