Head First Design Patterns

By Eric Freeman, Elisabeth Freeman, Kathy Sierra, Bert Bates
 October 2004 
Pages: 676 
ISBN 10: 0-596-00712-4  

Refactoring: Improving the Design of Existing Code (Addison-Wesley Object Technology Series) (Hardcover)

by Martin Fowler, Kent Beck, John Brant, William Opdyke, Don Roberts

ISBN 10: 0-201-48567-2

Effective Java (2nd Edition) (Java Series) (Paperback)

by Joshua Bloch

ISBN 10: 0-321-35668-3

Java Precisely (2nd Edition) (Paperback)

by Peter Sestoft

ISBN 10: 0-262-69325-9

This is a useful reference, but not required for the course.