I bought this book after having difficulty with the Java module in my college course. I bought this, and the larger book, teach yourself Java in 21 days. I've now finished the 24hours book, and found it a fantastic help. Each chapter(hour) is well thought out, and adds a new string to your Java bow, if you'll excuse the cliché. The author is sarcastic but knowledgeable, and comes across as genuine, as opposed to many other programming books which treat the reader as an idiot.
Be warned though-you MUST do the practicals included, as well as the activities at the end of each chapter. Without these, nothing will sink in, and the practicals are so easily done, the hour target is very achievable. Don't expect to know every single piece of Java-but do expect to get an overall introduction, and a great start to this area of programming.