根据文本字段更新组合框值

Question

public class SelectFrame extends JFrame {

    private JPanel contentPane;
    private JTextField zipText;
    JComboBox<String> agegroupBox;
    HealthData data = new HealthData();
    private boolean isinserted;
    ArrayList<String> list;

    /**
     * Create the frame.
     */
    public SelectFrame() {
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        setBounds(100, 100, 450, 150);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);

        agegroupBox = new JComboBox();

        zipText = new JTextField();
        zipText.setColumns(10);
        zipText.getDocument().addDocumentListener(new DocumentListener() {

            @Override
            public void insertUpdate(DocumentEvent e) {
                isinserted = true;

                if(validation())
                {
                    int zipcode = Integer.parseInt(zipText.getText()); 
                    list = new ArrayList<String>(data.selectAgeGroup(zipcode));
                }
            }

            @Override
            public void removeUpdate(DocumentEvent e) {
                // TODO Auto-generated method stub

            }

            @Override
            public void changedUpdate(DocumentEvent e) {


agegroupBox.addActionListener(new ActionListener () {
                    public void actionPerformed(ActionEvent e) {
                        if(isinserted = true)
                        {
                            for(int i = 0; i < list.size(); i++) {
                                System.out.println(list.get(i).toString());
                                agegroupBox.addItem(list.get(i));
                            }

                        }
                    }
                });

            }
            public boolean validation()
            {
                try {
                    int zipcode = Integer.parseInt(zipText.getText()); 
                }catch (NumberFormatException a) {
                    JOptionPane.showMessageDialog(null, "Zipcode entered is invalid", "Error", JOptionPane.ERROR_MESSAGE);
                    new SelectFrame();              
                }
                return true;
            }
                });
        agegroupBox.addActionListener(new ActionListener () {
            public void actionPerformed(ActionEvent e) {
                if(isinserted = true)
                {
                    for(int i = 0; i < list.size(); i++)
                        agegroupBox.addItem(list.get(i));                   
                }
            }
        });

我试图在文本字段中插入zipcode时将数据从数据库加载到comboBox中，我正在使用2个侦听器进行组合框和文本字段，但是当我运行此代码时，组合框中输入文本字段时没有任何变化，如果将zipcode插入文本字段，如何更新组合框？