[java] urgent help needed

[aerus]

Hello,
i am a newbie in Java and try to make a program for a horse race. I made an interface with swing but I don't know how to add an ActionListener for the ComboBox. Could someone please help me? It is very important...
here is my program:

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

public class Wette extends JFrame {

void buildConstraints(GridBagConstraints gbc, int gx, int gy,
int gw, int gh, int wx, int wy) {

gbc.gridx = gx;
gbc.gridy = gy;
gbc.gridwidth = gw;
gbc.gridheight = gh;
gbc.weightx = wx;
gbc.weighty = wy;
}

public Wette() {
super("Pferderennen");
setSize(400, 200);
GridBagLayout gridbag = new GridBagLayout();
GridBagConstraints constraints = new GridBagConstraints();
JPanel pane = new JPanel();
pane.setLayout(gridbag);

// title label
buildConstraints(constraints, 1, 0, 5, 1, 0, 0);
constraints.fill = GridBagConstraints.HORIZONTAL;
constraints.anchor = GridBagConstraints.EAST;
JLabel label0 = new JLabel("Sieg Wette", JLabel.LEFT);
gridbag.setConstraints(label0, constraints);
pane.add(label0);

// quoten label
buildConstraints(constraints, 0, 2, 1, 1, 0, 0);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.WEST;
JLabel labelq = new JLabel("Quoten", JLabel.CENTER);
gridbag.setConstraints(labelq, constraints);
pane.add(labelq);

// pf_wählen label
buildConstraints(constraints, 0, 3, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.WEST;
JLabel labelw = new JLabel("Pferde wählen :", JLabel.CENTER);
gridbag.setConstraints(labelw, constraints);
pane.add(labelw);

// einsatz label
buildConstraints(constraints, 0, 4, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.WEST;
JLabel labele = new JLabel("Ihr Einsatz eingeben :", JLabel.CENTER);
gridbag.setConstraints(labele, constraints);
pane.add(labele);

// quote_1 label
buildConstraints(constraints, 1, 1, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.CENTER;
JLabel label1 = new JLabel("1", JLabel.CENTER);
gridbag.setConstraints(label1, constraints);
pane.add(label1);

// quote_2 label
buildConstraints(constraints, 2, 1, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.CENTER;
JLabel label2 = new JLabel("2", JLabel.CENTER);
gridbag.setConstraints(label2, constraints);
pane.add(label2);

// quote_3 label
buildConstraints(constraints, 3, 1, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.CENTER;
JLabel label3 = new JLabel("3", JLabel.CENTER);
gridbag.setConstraints(label3, constraints);
pane.add(label3);

// quote_4 label
buildConstraints(constraints, 4, 1, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.CENTER;
JLabel label4 = new JLabel("4", JLabel.CENTER);
gridbag.setConstraints(label4, constraints);
pane.add(label4);

// quote_5 label
buildConstraints(constraints, 5, 1, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.CENTER;
JLabel label5 = new JLabel("5", JLabel.CENTER);
gridbag.setConstraints(label5, constraints);
pane.add(label5);

// quote_1 feld
buildConstraints(constraints, 1, 2, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JTextField tfield1 = new JTextField();
tfield1.setEditable(false);
gridbag.setConstraints(tfield1, constraints);
pane.add(tfield1);

// quote_2 feld
buildConstraints(constraints, 2, 2, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JTextField tfield2 = new JTextField();
tfield2.setEditable(false);
gridbag.setConstraints(tfield2, constraints);
pane.add(tfield2);

// quote_3 feld
buildConstraints(constraints, 3, 2, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JTextField tfield3 = new JTextField();
tfield3.setEditable(false);
gridbag.setConstraints(tfield3, constraints);
pane.add(tfield3);

// quote_4 feld
buildConstraints(constraints, 4, 2, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JTextField tfield4 = new JTextField();
tfield4.setEditable(false);
gridbag.setConstraints(tfield4, constraints);
pane.add(tfield4);

// quote_5 feld
buildConstraints(constraints, 5, 2, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JTextField tfield5 = new JTextField();
tfield5.setEditable(false);
gridbag.setConstraints(tfield5, constraints);
pane.add(tfield5);


// Pferd wählen

buildConstraints(constraints, 1, 3, 5, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JComboBox jcb = new JComboBox();
jcb.addItem("");
jcb.addItem("Pferd 1");
jcb.addItem("Pferd 2");
jcb.addItem("Pferd 3");
jcb.addItem("Pferd 4");
jcb.addItem("Pferd 5");

gridbag.setConstraints(jcb, constraints);
pane.add(jcb);


// einsatz feld
buildConstraints(constraints, 2, 4, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.HORIZONTAL;
JTextField tfieldE = new JTextField();
gridbag.setConstraints(tfieldE, constraints);
pane.add(tfieldE);

// euro label
buildConstraints(constraints, 3, 4, 1, 1, 1, 1);
constraints.fill = GridBagConstraints.NONE;
constraints.anchor = GridBagConstraints.WEST;
JLabel labeleur = new JLabel("€", JLabel.CENTER);
gridbag.setConstraints(labeleur, constraints);
pane.add(labeleur);


// Content Pane
setContentPane(pane);
}
public static void main(String[] arguments) {
Wette frame = new Wette();
ExitWindow exit = new ExitWindow();
frame.addWindowListener(exit);
frame.show();
}
}



class ExitWindow extends WindowAdapter {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
}

thanks in advance,
greetings from Germany