JTabbedPaneのタブエリアをダブルクリックして新規タブを作成する

JTabbedPane tabbedPane = new JTabbedPane();
tabbedPane.setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);
Action addAction = new AbstractAction() {
  @Override public void actionPerformed(ActionEvent e) {
    JTabbedPane tabs = (JTabbedPane) e.getSource();
    int cnt = tabs.getTabCount();
    tabs.addTab("Untitled-" + cnt, new JScrollPane(new JTextArea()));
    tabs.setSelectedIndex(cnt);
  }
};
InputMap im = tabbedPane.getInputMap(WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
ActionMap am = tabbedPane.getActionMap();
String addKey = "AddTab";
addAction.putValue(Action.ACTION_COMMAND_KEY, addKey);
im.put(KeyStroke.getKeyStroke("ctrl N"), addKey);
am.put(addKey, addAction);

tabbedPane.addMouseListener(new MouseAdapter() {
  @Override public void mouseClicked(MouseEvent e) {
    boolean leftButton = e.getButton() == MouseEvent.BUTTON1;
    boolean doubleClick = e.getClickCount() >= 2;
    JTabbedPane tabs = (JTabbedPane) e.getComponent();
    int idx = tabs.indexAtLocation(e.getX(), e.getY());
    Rectangle r = getTabAreaBounds(tabs);
    if (leftButton && doubleClick && idx < 0 && r.contains(e.getPoint())) {
      Optional.ofNullable(tabs.getActionMap().get(addKey)).ifPresent(a -> {
        ActionEvent ae = new ActionEvent(
            tabs, ActionEvent.ACTION_PERFORMED, addKey);
        a.actionPerformed(ae);
      });
    }
  }
});