Once again, I'm really very happy that I bought this book. Such a gentle introduction to such a vast and deep subject. I especially like how the authors have managed to introduce the concept of Interfaces and until now made it clear how two such interfaces exist and can be implemented. Very well done! I have read books where they blow horns and scare you to death before they introduce the concept of Interfaces. I am one of those people who have been traumatized by interfaces. In fact it is such a basic concept, very similar to classes, as illustrated in this book.
Clarity... Keep it up!