Three Parts of a GUI Program

A GUI program consists of three types of software:

1. Graphical Components that make up the Graphical User Interface.
2. Listener methods that receive the events and respond to them.
3. Application methods that do useful work for the user.

You get graphical components by constructing Swing objects. Listener methods and application methods are Java methods that you write. You have already written application methods: they are just ordinary Java methods that perform useful computations.

Your web browser has components (such as the "back" and "forward" buttons), listener methods that receive events (such as a click on the "back" button) and application methods that do useful things (such as moving back one page.)

To write a GUI application, keep the three types software separated (while keeping the big picture in mind.) In a big software project an entire team of programmers is assigned to each of the tasks.