Не могу отобразить собственный ComboBox в форме - Java

public class ComboBoxDemo {
 
    private List<Country> countries;
    private JComboBox cBox;
 
    public ComboBoxDemo(JFrame frame) {
        countries = createCountryList();
        cBox = createComboBox(countries);
        frame.add(cBox);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
 
    private JComboBox createComboBox(List<Country> countries) {
        final JComboBox comboBox = new JComboBox(countries.toArray());
        comboBox.setRenderer(new ComboBoxRenderer());
        comboBox.addItemListener(new ItemListener() {
            @Override
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    Country country = (Country) comboBox.getSelectedItem();
                    System.out.println(country.getIso());
                }
            }
        });
        return comboBox;
    }
 
    private class ComboBoxRenderer extends DefaultListCellRenderer {
 
        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected,
                boolean cellHasFocus) {
            JLabel label = (JLabel) super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
            Country country = (Country) value;
            label.setText(country.getName());
            return label;
        }
    }
 
    private List<Country> createCountryList() {
        List<Country> list = new ArrayList<>();
        list.add(new Country("Afghanistan", "AF"));
        list.add(new Country("Г…land Islands", "AX"));
        list.add(new Country("Albania", "AL"));
        return list;
    }
 
    public class Country {
        private String name;
        private String iso;
 
        public Country(String name, String iso) {
            this.name = name;
            this.iso = iso;
        }
 
        public String getName() {
            return name;
        }
 
        public String getIso() {
            return iso;
        }
    }
 
}

public class GUI {
    String RetVal1;
    String[][] RetValArr;
    private JFrame frame;
    private JLabel lblNewLabel;
    private JTextField Name_textField;
 
    private JFormattedTextField Phone_formattedTextField;
 
    static Connection conn3 = null;
    static int EC1;
    static int CurrentEntry;
    static String CurrentEntrySTR;
 
    private JTextField CurrentEnty_textField;
    private JTable table;
 
    public static void main(String[] args) {
 
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    GUI window = new GUI();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
 
    }
    public GUI() {
        initialize();
    }
 
    private void initialize() {
 
        frame = new JFrame();
        frame.setBounds(100, 100, 504, 513);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);
 
        JComboBox From_comboBox = new JComboBox();
        From_comboBox.setModel(new DefaultComboBoxModel(new String[] { "1", "2", "3", "4", "5" }));
        From_comboBox.setEditable(true);
        From_comboBox.setMaximumRowCount(2);
        From_comboBox.setBounds(274, 194, 186, 23);
        frame.getContentPane().add(From_comboBox);
        new ComboBoxDemo(frame);
 
        JComboBox Status_comboBox = new JComboBox();
        Status_comboBox.setBounds(274, 281, 186, 23);
        frame.getContentPane().add(Status_comboBox);
 
        CurrentEnty_textField = new JTextField();
    }
}