Problem
The best way to learn how to do object-oriented programming is to go back through the examples and exercises of previous chapters and see which ones are easier or more naturally written using classes and objects. You can also create object-oriented programs that represent things in the real world. For example, what classes would you use to model the stars, planets, moons, rings, and comets that make up a solar system? What methods should each class have? How and where would you keep track of things like orbital parameters? How would you prevent programmers from accidentally putting a star in orbit around a comet or something equally silly?