protected JPopupMenu buildTableMenu() {
		JPopupMenu ans = new JPopupMenu();
		String[] show = { "", "ɾ", "޸" };
		String[] action = { "add", "remove", "modify" };
		int i;
		for (i = 0; i < show.length; ++i) {
			JMenuItem item = new JMenuItem(show[i]);
			item.setActionCommand(action[i]);
			item.addActionListener(this);
			ans.add(item);
		}
		return ans;
	}