20.5. Stroking Shape Outlines
Just as a Graphics2D object's current paint determines how its shapes are filled, its current stoke determines how its shapes are outlined. The current stroke determines such drawing features as line thickness, line dashing, and end styles. In the old days, lines were one pixel wide and that was that. With Java 2D, line thickness can be set with floating-point accuracy and the results, like everything else, are subject to the rendering pipeline's transformations and scaling.
To set the current stroke in Graphics2D, call setStroke( ) with any implementation of the Stroke interface. Fortunately, the 2D API includes a BasicStroke class that probably does everything you need. Using BasicStroke, you can create dashed lines, control what decoration is added to line ends, and decide how the corners in an outline should be drawn.
By default, Graphics2D uses a solid stroke with a width of 1. In the previous Iguana example, the line width is changed just before the outline of the rounded rectangle is drawn, like so: