The best way to learn programming is practice. You are encouraged to try as many exercise problems as possible.

However, if you are really lazy and don't care about the grade, the $$$ you've spent, and your own future, then the following minimal exercise requirement list is for you.

• Chapter 2: Exercise 2.25 (no need to submit, but highly recommended)
• Chapter 3: Exercise 3.10 (no need to submit, but highly recommended)
• Chapter 4: Exercise 4.29, 4.30 (no need to submit, but highly recommended)
• Challenging Homework 1: The Java City
• Chapter 6: Exercise 6.27, 6.28, 6.29, 6.30, 6.31 (no need to submit, but highly recommended)
• Chapter 7: Exercise 7.10, 7.22, 7.24 (no need to submit, but highly recommended)
• Chapter 8: Exercise 8.10, 8.12, 8.13, 8.14 (no need to submit, but highly recommended)
• Challenging Homework 2: Trade or War!
  
• Chapter 10: Exercise 10.7, 10.8, 10.9 (no need to submit, but highly recommended)
• Chapter 13: Exercise 13.17, 13.18, 13.19 (no need to submit, but highly recommended)
• Chapter 16: Exercise 16.8, 16.9 (for those who have learned recursion) (no need to submit, but highly recommended)

Upload all your works to an online service (e.g. Box.net, pastebin). Then write a short paragraph in your personal Programming Portfolio before the due dates to describe what you have done. I would visit your sites to grade the assignments.