Nearly every Java application involves multiple classes. As you have learned, designing a program around classes and objects is a key feature of object$-$oriented programming and provides many benefits, such as more readable and maintainable code. However, it is not enough to just have multiple classes. You also need to make sure that these classes can work together within a program. This involves making sure that any relationships, such as inheritance, are properly implemented in the code. It also involves having a main$()$ method, usually located in a special class called the $$Driver$$ class, that runs the program.