JToggleButtonをFlowLayoutで重ねて表示する

private static AbstractButton makeButton(
    String title, Color color, final int overlap, boolean first) {
  final ToggleButtonBarCellIcon icon = new ToggleButtonBarCellIcon();
  AbstractButton b = new JToggleButton(title) {
    @Override public boolean contains(int x, int y) {
      if (Objects.nonNull(icon) && Objects.nonNull(icon.area)) {
        return icon.area.contains(x, y);
      } else {
        return super.contains(x, y);
      }
    }

    @Override public Dimension getPreferredSize() {
      return new Dimension(icon.getIconWidth(), icon.getIconHeight());
    }

    @Override protected void paintComponent(Graphics g) {
      icon.paintIcon(this, g, 0, 0);
      super.paintComponent(g);
    }
  };
  b.setIcon(new Icon() {
    @Override public void paintIcon(Component c, Graphics g, int x, int y) {
      g.setColor(Color.GRAY);
      g.drawOval(x, y, 12, 12);
    }

    @Override public int getIconWidth() {
      return 12;
    }

    @Override public int getIconHeight() {
      return 12;
    }
  });
  b.setContentAreaFilled(false);
  int th = ToggleButtonBarCellIcon.TH;
  if (first) {
    b.setBorder(BorderFactory.createEmptyBorder(
        0, LINE_WIDTH + BI_GAP, 0, th));
  } else {
    b.setBorder(BorderFactory.createEmptyBorder(
        0, th + LINE_WIDTH + BI_GAP, 0, th));
  }
  b.setHorizontalAlignment(SwingConstants.LEFT);
  b.setFocusPainted(false);
  b.setOpaque(false);
  b.setBackground(color);
  return b;
}

private static JPanel makePanel(int overlap) {
  JPanel p = new JPanel(new FlowLayout(FlowLayout.LEADING, -overlap, 0)) {
    @Override public boolean isOptimizedDrawingEnabled() {
      return false;
    }
  };
  p.setBorder(BorderFactory.createEmptyBorder(0, overlap, 0, 0));
  p.setOpaque(false);
  return p;
}

private static JComponent makeBreadcrumbList(
    int overlap, Color color, List<String> list) {
  JPanel p = makePanel(overlap + LINE_WIDTH);
  ButtonGroup bg = new ButtonGroup();
  boolean f = true;
  for (String title : list) {
    AbstractButton b = makeButton(title, color, overlap, f);
    p.add(b);
    bg.add(b);
    f = false;
  }
  return p;
}