in netbeans.apache.org/src/old_content/content/tutorials/74/images/paintapp_70_PaintCanvas.java [97:105]
public void paint(Graphics g) {
((Graphics2D) g).setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
Point p = new Point(getWidth() / 2, getHeight() / 2);
int half = getBrushDiameter() / 2;
int diam = getBrushDiameter();
g.setColor(getColor());
g.fillOval(p.x - half, p.y - half, diam, diam);
}