Swing/TabAreaLayout のバックアップ(No.1)

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 vp = (JViewport) SwingUtilities.getAncestorOfClass(JViewport.class, c);
  Rectangle rect = SwingUtilities.convertRectangle(c, tab.getBounds(), vp);
  if (vp.getBounds().contains(rect)) {
    return null;
  }
  JLabel l = (JLabel) tab.getComponent(0);
  String title = l.getText();
  JMenuItem mi = new JRadioButtonMenuItem(title);
  mi.addActionListener(e -> {
    tab.setSelected(true);
    cardLayout.show(contentsPanel, title);
    tab.scrollRectToVisible(rect);
  });
  return mi;
}