JPopupMenuをボタンの長押しで表示

class PressAndHoldHandler extends AbstractAction implements MouseListener {
  public final JPopupMenu pop = new JPopupMenu();
  public final ButtonGroup bg = new ButtonGroup();
  private AbstractButton arrowButton;
  private final Timer holdTimer = new Timer(1000, e -> {
    if (arrowButton != null && arrowButton.getModel().isPressed()
        && holdTimer.isRunning()) {
      holdTimer.stop();
      pop.show(arrowButton, 0, arrowButton.getHeight());
      pop.requestFocusInWindow();
    }
  });

  public PressAndHoldHandler() {
    super();
    holdTimer.setInitialDelay(1000);
    pop.setLayout(new GridLayout(0, 3, 5, 5));
    for (MenuContext m: makeMenuList()) {
      AbstractButton b = new JRadioButton(m.command);
      b.setActionCommand(m.command);
      b.setForeground(m.color);
      b.setBorder(BorderFactory.createEmptyBorder());
      b.addActionListener(e -> {
        System.out.println(e.getActionCommand());
        pop.setVisible(false);
      });
      pop.add(b);
      bg.add(b);
    }
  }

  private List<MenuContext> makeMenuList() {
    return Arrays.asList(
      new MenuContext("BLACK", Color.BLACK),
      new MenuContext("BLUE", Color.BLUE),
      new MenuContext("CYAN", Color.CYAN),
      new MenuContext("GREEN", Color.GREEN),
      new MenuContext("MAGENTA", Color.MAGENTA),
      new MenuContext("ORANGE", Color.ORANGE),
      new MenuContext("PINK", Color.PINK),
      new MenuContext("RED", Color.RED),
      new MenuContext("YELLOW", Color.YELLOW));
  }

  @Override public void actionPerformed(ActionEvent e) {
    System.out.println("actionPerformed");
    if (holdTimer.isRunning()) {
      ButtonModel model = bg.getSelection();
      if (model != null) {
        System.out.println(model.getActionCommand());
      }
      holdTimer.stop();
    }
  }

  @Override public void mousePressed(MouseEvent e) {
    System.out.println("mousePressed");
    Component c = e.getComponent();
    if (SwingUtilities.isLeftMouseButton(e) && c.isEnabled()) {
      arrowButton = (AbstractButton) c;
      holdTimer.start();
    }
  }

  @Override public void mouseReleased(MouseEvent e) {
    holdTimer.stop();
  }

  @Override public void mouseExited(MouseEvent e) {
    if (holdTimer.isRunning()) {
      holdTimer.stop();
    }
  }

  @Override public void mouseEntered(MouseEvent e) {
    /* not needed */
  }

  @Override public void mouseClicked(MouseEvent e) {
    /* not needed */
  }
}