Highly recommended to push your Java to the next level because of the seriously detailed but also clear explanations 'at the edges' of the Java libraries.
I subscribe to the saying 'perfection is reached when there is nothing more you can take away from a program', in practice gaining simplicity from reliance on quality libraries. This book shows you JDK libraries that are _really_ useful, explaining them so well you don't need to dig into the source or visit hundreds of forums to gain real confidence in using them.
At £22 this is a steal, and even if you think you know all there is 'useful' to know about Java I'm positive this can show you even more. And when they sort out Java 7 I look forward to the next edition of this book to find all the juicy new bits.
5 stars EVEN THOUGH the Swing-based examples are annoying, because the text is so well written that it makes running examples almost unnecessary. And 5 stars to the editorial team for the polish - I'm sure there are typos in such a long book but I haven't encountered one yet, beating Apress and other much poorer publishing houses on almost every level.