I have the GoF book. But I did not use it very much for the exam. Typically people who report there scores on the exam do well on patterns. Some of the patterns answers will come from use of Java on real projects.
The GoF book is in C++ and OMT. Mark Grand's book is in Java and UML.
All you may need is the material in Sun's
SCEA study guide. You may not need that much.
Of course, knowledge of patterns is valuable in other areas than the
test.
J2EE seems to have its own patterns too.