Below are some lessons on env3d that you can use as exercises to re-enforce Object Oriented concepts. Each of these lessons are best used as supplementary material to the corresponding chapter of Objects First with Java book by Barnes & Kolling. The lessons are designed to be coded using the introductory java development program BlueJ. You can download BlueJ here. TIP: Double clicking on the code listing area would select the entire code section. You can then copy and paste the code.