通过ComboBox创建JLabel

Question

我要做的是创建一个依赖于组合框中选择的JLabel，即如果选择“History Book”，则创建标签“Enter period”，如果选择“Fictional Book”，则创建标签“Enter类型”。事情是无论我选择什么标签是不可见的，它应该保持空的地方。我错的任何想法？

这是我的代码：

JComboBox comboBox = new JComboBox(bookTypes);
    comboBox.setModel(new DefaultComboBoxModel(new String[] {"History Book", "Fictional Book", "Textbook"}));
    comboBox.setToolTipText("Choose the type of book here!");
    comboBox.setBounds(196, 48, 156, 20);
    ActionListener cbActionListener = new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            String s = (String) comboBox.getSelectedItem();
            if(s.equals("History Book")){
                JLabel lblWriteThePeriod = new JLabel("Write the Period:");
                lblWriteThePeriod.setBounds(10, 317, 142, 14);
                dialog.getContentPane().add(lblWriteThePeriod);
            }else if(s.equals("Fictional Book")){
                JLabel lblWriteTheGenre = new JLabel("Write the genre:");
                lblWriteTheGenre.setBounds(10, 317, 142, 14);
                dialog.getContentPane().add(lblWriteTheGenre);
            }
        }           
    };
    comboBox.addActionListener(cbActionListener);
    dialog.getContentPane().add(comboBox);
dialog.setVisible(true);