A Graphics object is passed to the paintComponent() method of any component that needs to be painted. AFAIK, this happens with all components. The Graphics class provides functions that allow you to paint on a window or other component. These methods include drawLine(), drawRect(), and many others. For more details,
you should look at
the API documentation for the Graphics class. It lists all the methods that are available for your use. In fact, you should bookmark the index for
the API docs for the version of the
Java SDK that you are using and learn how to navigate it. These documents provide most of the information you need about any class in the API.
HTH
Layne