I have not yet seen any books about object design in Java that I particularly like. Several are expected to be coming out in the next few months though. One good general book I like is The Tao of Objects by Gary Entsminger (M&T Books, 1995, $27.95, possibly out of print). Although this book was written before Java appeared, it's nonetheless a good inroduction to the basics of object oriented programming.
Once you've mastered the material in that book you might want to explore the following:
The Tao of Objects teaches mostly the design of classes. The next logical step, which Ambler's book explores, is the design of interacting systems of classes and objects.
Finally, the largest development in object oriented progrmming in the 90's has been the recognition of meta-structures in programming that go beyond single classes. These are referred to as patterns, and the definitivie introductory text on this subject is
