这个JComboBox不会打开新的JFrame

Question

我编写的代码创建了一个带有三个选项的JComboBox，并且在选择一个时应该打开一个新的JFrame，但没有任何反应。我哪里出错？

    JComboBox comboBox = new JComboBox();
    comboBox.addActionListener(new ActionListener() {

    public void actionPerformed(ActionEvent arg0) {
            JComboBox comboBox = (JComboBox) arg0.getSource();
            Object newItem = comboBox.getSelectedItem();

             boolean same = newItem.equals(oldItem);
             oldItem = newItem;

             if (" Loan".equals(arg0.getActionCommand())){
                 Loan loan = new Loan();
                 loan.setVisible(true);
                 frame.setVisible(false);

             }
             else if (" Return".equals(arg0.getActionCommand())){
                 //Code to open new jframe.
             }
             else if (" Renew".equals(arg0.getActionCommand())){
                 //Code to open new jframe.
             }
        }
    });