JTabbedPaneのタブエリアレイアウトを変更して一覧表示ボタンなどを追加する

protected CardLayoutTabbedPane() {
  super(new BorderLayout());
  setBorder(BorderFactory.createEmptyBorder(1, 1, 1, 1));
  setBackground(new Color(16, 16, 16));
  tabPanel.setInheritsPopupMenu(true);
  hiddenTabs.addActionListener(e -> {
    JButton b = (JButton) e.getSource();
    Point p = b.getLocation();
    JPopupMenu popup = new JPopupMenu();
    for (int i = 0; i < tabPanel.getComponentCount(); i++) {
      JMenuItem mi = makeRadioMenuItem(tabPanel, i);
      if (mi != null) {
        popup.add(mi);
      }
    }
    p.x += b.getWidth() - popup.getPreferredSize().width - 1;
    p.y += b.getHeight();
    popup.show(b.getParent(), p.x, p.y);
  });
  JPanel buttons = new JPanel(new GridBagLayout());
  buttons.add(hiddenTabs);
  JPanel header = new JPanel(new BorderLayout());
  header.add(new JLayer<>(tabArea, new HorizontalScrollLayerUI()));
  header.add(buttons, BorderLayout.EAST);
  add(header, BorderLayout.NORTH);
  add(contentsPanel);
}

private JMenuItem makeRadioMenuItem(Container c, int i) {
  JToggleButton tab = (JToggleButton) c.getComponent(i);
  JViewport viewport = tabArea.getViewport();
  Rectangle r = tab.getBounds();
  if (viewport.getViewRect().contains(r)) {
    return null;
  }
  JLabel label = (JLabel) tab.getComponent(0);
  String title = label.getText();
  JMenuItem mi = new JRadioButtonMenuItem(title);
  mi.addActionListener(e -> {
    tab.setSelected(true);
    cardLayout.show(contentsPanel, title);
    viewport.scrollRectToVisible(SwingUtilities.convertRectangle(c, r, viewport));
  });
  return mi;
}