JCheckBoxのチェックアイコンを一行目中央に配置する

class WindowsVerticalAlignmentCheckBoxUI extends WindowsCheckBoxUI {
  @Override public synchronized void paint(Graphics g, JComponent c) {
    AbstractButton b = (AbstractButton) c;
    // ...
    // Paint the radio button
    int y = HtmlViewUtil.getFirstLineCenterY(text, b, iconRect);
    getDefaultIcon().paintIcon(c, g, iconRect.x, iconRect.y + y);
    // ...
  }

  public static int getFirstLineCenterY(
      String text, AbstractButton c, Rectangle iconRect) {
    int y = 0;
    if (text != null && c.getVerticalTextPosition() == SwingConstants.TOP) {
      Object o = c.getClientProperty(BasicHTML.propertyKey);
      if (o instanceof View) {
        View v = (View) o;
        try {
          Element e = v.getElement().getElement(0);
          Shape s = new Rectangle();
          Position.Bias b = Position.Bias.Forward;
          s = v.modelToView(
              e.getStartOffset(), b, e.getEndOffset(), b, s);
          y = (int) (.5 + Math.abs(
              s.getBounds().height - iconRect.height) * .5);
        } catch (BadLocationException ex) {
          ex.printStackTrace();
        }
      }
    }
    return y;
  }
}