All exercises are from the book Thinking in Java:

Chapter 7 - Polymorphism

Exercises 1 - 5.

Chapter 8 - Interfaces & Inner Classes

Exercises 2, 4 and 5.

Chapter 9 - Error Handling with Exceptions

Exercises 1 - 5.

Chapter 13 - Concurrency

Exercises 1, 2 and 5.

Chapter 14 - Creating Windows & Applets

Exercises 17 - 21.

Chapter 15 - Discovering Problems has excellent exercises about testing. If you can, do the first 5. Those tests can help you a lot during development of your assignment program.