in netbeans.apache.org/src/old_content/content/tutorials/74/images/paintapp_70_PaintCanvas.java [115:125]
public void mouseClicked(MouseEvent e) {
Point p = e.getPoint();
int half = brushDiameter / 2;
Graphics2D g = getImage().createGraphics();
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g.setPaint(getColor());
g.fillOval(p.x - half, p.y - half, brushDiameter, brushDiameter);
g.dispose();
repaint(p.x - half, p.y - half, brushDiameter, brushDiameter);
}