From Geography to Cartography - Programming GPS and OpenStreetMap Applications with Java - page 60

Creating the scales as visual components opens the option to place them
inside a Swing Container and draw them.
With these conversion methods, any GPS position can be converted to
spatial coordinates. The next \hook" (a way for customizing the handling
of some event or process) to Swing is the method that actually paints the
component:
protected void paintComponent(Graphics g)
Figure5.1. An overview of the roafx.gui.map package to build a minimum ROAF
GUI front end. The drawing of geographical coordinates and map primitives
takes place in the MapPanel . The transformation from decimal (geographical)
coordinates to pixel values is calculated in the MapScalePanel s.