Place a JFormattedTextField on a JPanel, add a mask. NB creates this code:

    try {
      jFormattedTextField1.setFormatterFactory(new javax.swing.text.DefaultFormatterFactory(new javax.swing.text.MaskFormatter("###-####")));
    } catch (java.text.ParseException ex) {
      ex.printStackTrace();
    }

After that, right click on the formatterFactory an press restore default value. NB leaves the following code:

    try {
    } catch (java.text.ParseException ex) {
      ex.printStackTrace();
    }

in the private void initComponents(), that can not be edited. So you have to open the file in a Texteditor and delete this code.