Swing/SelectedTabTitleText のバックアップ(No.1)

tabs.addChangeListener(e -> {
  JTabbedPane tabbedPane = (JTabbedPane) e.getSource();
  if (tabbedPane.getTabCount() <= 0) {
    return;
  }
  int idx = tabbedPane.getSelectedIndex();
  for (int i = 0; i < tabbedPane.getTabCount(); i++) {
    Component c = tabbedPane.getTabComponentAt(i);
    if (c instanceof JLabel) {
      ((JLabel) c).setText(i == idx ? tabbedPane.getTitleAt(i) : null);
    }
  }
});

// ...
private static void addTab(JTabbedPane tabbedPane, TabTitle tt, Component c) {
  tabbedPane.addTab(tt.title, c);
  URL url = tt.url;
  Icon icon = Objects.nonNull(url) ? new ImageIcon(url) : UIManager.getIcon("html.missingImage");
  JLabel label = new JLabel(null, icon, SwingConstants.CENTER) {
    @Override public Dimension getPreferredSize() {
      Dimension d = super.getPreferredSize();
      Container c = SwingUtilities.getAncestorOfClass(JTabbedPane.class, this);
      if (c instanceof JTabbedPane) {
        int tp = ((JTabbedPane) c).getTabPlacement();
        if (tp == TOP || tp == BOTTOM) {
          d.height = icon.getIconHeight() + tabbedPane.getFont().getSize() + getIconTextGap();
        }
      }
      return d;
    }
  };
  label.setVerticalTextPosition(SwingConstants.BOTTOM);
  label.setHorizontalTextPosition(SwingConstants.CENTER);
  tabbedPane.setTabComponentAt(tabbedPane.getTabCount() - 1, label);
}