Well from my experience of preparing for SCJP2, I would suggest that you make your own code. Just visualize the problem and try to write a program for that. Also you can take any code from the book and make a arbitrary change in it and see how this change has changed the result. Frankly speaking i was greatly helped by this technique in becoming a SCJP and boosted my confidence for the real exam. All the best!!!
Vikas Kaushik SCJP2
subject: Any guide on how to practise hands on for JCP test