You can see a preview at the book's site, along with resources for students and teachers.
This book isn't just for class use. Greenfoot is a great way to learn to use Java. You can learn the basics of programming with graphics and sound that are far easier to use than in standard Java. Greenfoot and BlueJ both illustrate basic concepts of Object Oriented programming in a way that makes them clearer than any other method I've seen. You can deal with objects as objects, see what their member methods and fields are, and use them outside the program itself.
So, if you're in a class or self-taught, I recommend using Greenfoot along with the online resources, and this book. The book can be completed in a short time and leave you ready to write your own programs with Greenfoot, or move on to using Java without Greenfoot if you wish.