The layout of the book is extremely easy to follow and reference. The individual concepts are grouped into "Items" and those items are grouped into topics that are the chapters of the book. At the very least, every programmer needs to read the first 18 items. I'll give you a brief example of the power of this book.

Item 7: Obey the general contract when overriding equals

Every Java developer tends to think he/she knows when and how to override the Object.equals method. This item explains the core concepts of the method and when and how to implement it. It's over 10 pages of explanation with code examples. I have used the techniques that Josh explained in almost every class I've written since I read this item. Before I read this book almost all of my equals methods failed to follow the general contract.

I could go on all day, but I know this isn't the place for that, so I really do hope that if you're a Java developer, you will own this book if you don't already. The full table of contents can be seen on the book's site.