JToggleButtonからポップアップメニューを開く

class MenuArrowIcon implements Icon {
  @Override public void paintIcon(Component c, Graphics g, int x, int y) {
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setPaint(Color.BLACK);
    g2.translate(x, y);
    g2.drawLine(2, 3, 6, 3);
    g2.drawLine(3, 4, 5, 4);
    g2.drawLine(4, 5, 4, 5);
    g2.dispose();
  }

  @Override public int getIconWidth()  {
    return 9;
  }

  @Override public int getIconHeight() {
    return 9;
  }
}

class MenuToggleButton extends JToggleButton {
  private static final Icon ARROW_ICON = new MenuArrowIcon();
  private JPopupMenu popup;

  protected MenuToggleButton() {
    this("", null);
  }

  protected MenuToggleButton(Icon icon) {
    this("", icon);
  }

  protected MenuToggleButton(String text) {
    this(text, null);
  }

  protected MenuToggleButton(String text, Icon icon) {
    super();
    Action action = new AbstractAction(text) {
      @Override public void actionPerformed(ActionEvent e) {
        Component b = (Component) e.getSource();
        Optional.ofNullable(getPopupMenu()).ifPresent(p -> p.show(b, 0, b.getHeight()));
      }
    };
    action.putValue(Action.SMALL_ICON, icon);
    setAction(action);
    setFocusable(false);
    setBorder(BorderFactory.createEmptyBorder(4, 4, 4, 4 + ARROW_ICON.getIconWidth()));
  }

  public JPopupMenu getPopupMenu() {
    return popup;
  }

  public void setPopupMenu(JPopupMenu pop) {
    this.popup = pop;
    pop.addPopupMenuListener(new PopupMenuListener() {
      @Override public void popupMenuCanceled(PopupMenuEvent e) {
        /* not needed */
      }

      @Override public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
        /* not needed */
      }

      @Override public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
        setSelected(false);
      }
    });
  }

  @Override protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Dimension dim = getSize();
    Insets ins = getInsets();
    int x = dim.width - ins.right;
    int y = ins.top + (dim.height - ins.top - ins.bottom - ARROW_ICON.getIconHeight()) / 2;
    ARROW_ICON.paintIcon(this, g, x, y);
  }
}