A Class and an Object

When a program starts running there are no objects, just class definitions and a static main() method. Usually main() then constructs some objects and calls their methods to do the work of the program. In our example, main() constructs just one object and then calls that object's calculateMPG() method.

The picture shows the variable car in the static main() method referring to the object that has been constructed following the class definition of Car. The static main() method is part of the MilesPerGallon class.

In the picture, the class definitions are shown as pink clouds as a reminder that they are not full objects. The object in this picture is shown as a solid rectangle.