Swing/IconScrollBar のバックアップ(No.10)

class BasicIconScrollBarUI extends BasicScrollBarUI {
  @Override protected void paintThumb(
      Graphics g, JComponent c, Rectangle thumbBounds) {
    super.paintThumb(g, c, thumbBounds);
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
    Color oc = null;
    Color ic = null;
    JScrollBar sb = (JScrollBar) c;
    if (!sb.isEnabled() || thumbBounds.width > thumbBounds.height) {
      return;
    } else if (isDragging) {
      oc = SystemColor.activeCaption.darker();
      ic = SystemColor.inactiveCaptionText.darker();
    } else if (isThumbRollover()) {
      oc = SystemColor.activeCaption.brighter();
      ic = SystemColor.inactiveCaptionText.brighter();
    } else {
      oc = SystemColor.activeCaption;
      ic = SystemColor.inactiveCaptionText;
    }
    paintCircle(g2, thumbBounds, 6, oc);
    paintCircle(g2, thumbBounds, 10, ic);
    g2.dispose();
  }
  private void paintCircle(Graphics2D g2, Rectangle b, int w, Color c) {
    g2.setPaint(c);
    int ww = b.width - w;
    g2.fillOval(b.x + w / 2, b.y + (b.height - ww) / 2, ww, ww);
  }
}