JMenuItemの内部にJButtonを配置する

private static JMenuItem makeEditMenuItem(final JComponent edit) {
  JMenuItem item = new JMenuItem("Edit") {
    @Override public Dimension getPreferredSize() {
      Dimension d = super.getPreferredSize();
      d.width += edit.getPreferredSize().width;
      d.height = Math.max(edit.getPreferredSize().height, d.height);
      return d;
    }

    @Override protected void fireStateChanged() {
      setForeground(Color.BLACK);
      super.fireStateChanged();
    }
  };
  item.setEnabled(false);

  GridBagConstraints c = new GridBagConstraints();
  item.setLayout(new GridBagLayout());
  c.anchor  = GridBagConstraints.LINE_END;
  c.weightx = 1d;

  c.fill = GridBagConstraints.HORIZONTAL;
  item.add(Box.createHorizontalGlue(), c);
  c.fill = GridBagConstraints.NONE;
  item.add(edit, c);

  return item;
}

private static JPanel makeEditButtonBar(List<AbstractButton> list) {
  int size = list.size();
  JPanel p = new JPanel(new GridLayout(1, size, 0, 0)) {
    @Override public Dimension getMaximumSize() {
      return super.getPreferredSize();
    }
  };
  for (AbstractButton b: list) {
    b.setIcon(new ToggleButtonBarCellIcon());
    p.add(b);
  }
  p.setBorder(BorderFactory.createEmptyBorder(4, 10, 4, 10));
  p.setOpaque(false);
  return p;
}

private static AbstractButton makeButton(String title, Action action) {
  JButton b = new JButton(action);
  b.addActionListener(new ActionListener() {
    @Override public void actionPerformed(ActionEvent e) {
      JButton b = (JButton) e.getSource();
      Container c = SwingUtilities.getAncestorOfClass(JPopupMenu.class, b);
      if (c instanceof JPopupMenu) {
        ((JPopupMenu) c).setVisible(false);
      }
    }
  });
  b.setText(title);
  b.setVerticalAlignment(SwingConstants.CENTER);
  b.setVerticalTextPosition(SwingConstants.CENTER);
  b.setHorizontalAlignment(SwingConstants.CENTER);
  b.setHorizontalTextPosition(SwingConstants.CENTER);
  b.setBorder(BorderFactory.createEmptyBorder());
  b.setContentAreaFilled(false);
  b.setFocusPainted(false);
  b.setOpaque(false);
  b.setBorder(BorderFactory.createEmptyBorder());
  return b;
}