JRadioButtonを使ってToggleButtonBarを作成

class ToggleButtonBarCellIcon implements Icon {
  private static final Color TL = new Color(1f, 1f, 1f, .2f);
  private static final Color BR = new Color(0f, 0f, 0f, .2f);
  private static final Color ST = new Color(1f, 1f, 1f, .4f);
  private static final Color SB = new Color(1f, 1f, 1f, .1f);
  private Color ssc;
  private Color bgc;

  @Override public void paintIcon(Component c, Graphics g, int x, int y) {
    int r = 8;
    int w = c.getWidth();
    int h = c.getHeight();

    Container parent = c.getParent();
    if (parent == null) {
      return;
    }

    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
    Path2D p = new Path2D.Float();

    if (c == parent.getComponent(0)) {
      // JButton.segmentPosition: first
      // :first-child
      p.moveTo(x, y + r);
      p.quadTo(x, y, x + r, y);
      p.lineTo(x + w, y);
      p.lineTo(x + w, y + h);
      p.lineTo(x + r, y + h);
      p.quadTo(x, y + h, x, y + h - r);
    } else if (c == parent.getComponent(parent.getComponentCount() - 1)) {
      // JButton.segmentPosition: last
      // :last-child
      p.moveTo(x, y);
      p.lineTo(x + w - r, y);
      p.quadTo(x + w, y, x + w, y + r);
      p.lineTo(x + w, y + h - r);
      p.quadTo(x + w, y + h, x + w - r, y + h);
      p.lineTo(x, y + h);
    } else {
      // JButton.segmentPosition: middle
      p.moveTo(x, y);
      p.lineTo(x + w, y);
      p.lineTo(x + w, y + h);
      p.lineTo(x, y + h);
    }
    p.closePath();
    Area area = new Area(p);

    g2.setPaint(c.getBackground());
    g2.fill(area);

    ssc = TL;
    bgc = BR;
    if (c instanceof AbstractButton) {
      ButtonModel m = ((AbstractButton) c).getModel();
      if (m.isSelected() || m.isRollover()) {
        ssc = ST;
        bgc = SB;
      }
    }
    g2.setPaint(new GradientPaint(x, y, ssc, x, y + h, bgc, true));
    g2.fill(area);

    g2.setPaint(BR);
    g2.draw(area);

    g2.dispose();
  }

  @Override public int getIconWidth()  {
    return 80;
  }

  @Override public int getIconHeight() {
    return 20;
  }
}