Well howdy -- those articles are part of the "Campfire Stories" and they're at:
http://www.javaranch.com/campfire.jsp But since you asked
I wrote the first four (including pass-by-value, cup-size, how I taught my dog
polymorphism, and getting in touch with your inner class) and if you find 'em helpful, there's gonna be a whole BOOK with stories and other pictorial approaches to learning
Java (from O'Reilly) coming out in about 8 weeks. It's called "Head First Java" (a brain-friendly guide)
I reckon you'll see a few more Campfire Stories up here on javaranch real soon -- we'll pull a few of our favorites from the book and try to get 'em up here.
We also have a bunch of exercises and puzzles to go with it, and some of those will be up here at the ranch soon, too.
Cheers!
Kathy Sierra
(author, with Bert Bates, "Head First Java")
(author, "Cowgirl's Guide to Shameless Self-Promotion")