This is the book that makes you go "ahh" and then go running to you Java code to make some quick changes.
At JavaOne 2001, James Gosling stood up and said "go buy this book". So I did, and yeah, it's good. The book is made up of 57 rules, such as how to correctly implement equals, how to implement type safe enumerations, how to properly implement singleton pattern, when to and when not to use clone.... It's a combination of "gotchas", good style and practice and in the process explains a bunch of things I thought I understood, but hadn't really thought through.
It's required reading.
My rating: Recommended