Add Combobox values from listener using Swing

I am new in working with Swing. I have a requirement where I need to get data from Database and pop up in Combo box, when the combobox listener performs, it needs to load the values. I am not sure where I went wrong the values in the below code is not displaying. Can any one please correct me if I am wrong. Code:

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;

public class ComboBoxSelectionChange extends JFrame
{
    public ComboBoxSelectionChange ()
    {
        initialize();
    }

    private void initialize ()
    {
        setSize(300, 300);
        setLayout(new FlowLayout(FlowLayout.LEFT));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JComboBox comboBox = new JComboBox();
        comboBox.setEditable(true);
        final JTextArea textArea = new JTextArea(5, 15);
        textArea.setBorder(new BevelBorder(BevelBorder.LOWERED));

        comboBox.addItemListener(new ItemListener() {

            public void itemStateChanged (ItemEvent event)
            {
                String[] items = { "A", "B", "C", "D", "E", "F" };
                final DefaultComboBoxModel model = new DefaultComboBoxModel(
                        items);

                comboBox.setModel(model);

            }
        });

        getContentPane().add(comboBox);
        getContentPane().add(textArea);
    }

    public static void main (String[] args)
    {
        SwingUtilities.invokeLater(new Runnable() {
            public void run ()
            {
                new ComboBoxSelectionChange().setVisible(true);
            }
        });
    }
}

Try adding a popupmenu listener to JComboBox like :

comboBox.addPopupMenuListener( PopupMenuListener listener )
{

   protected void popupMenuWillBecomeVisible( PopupMenuEvent event )
   {
       //update your model
   }

}