JFrameWithPanel is not abstract and does not override abstract method actionPerformed(java.awt.event.ActionEvent) in java.awt.event.ActionListener public class JFrameWithPanel extends JFrame implements ActionListener

I Don't get this code. Book and Java site tells me this is the syntax for the method, but again this error shows up constantly.

import javax.swing.*;
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;
import java.lang.Math.*;
import java.lang.Integer.*;
import java.util.*;
import java.util.Random;
import java.io.*;
import java.text.*;
import java.text.DecimalFormat.*;

public class JFrameWithPanel extends JFrame implements ActionListener
{
 JButton button = new JButton("Exit");

 public JFrameWithPanel()
 {
  super("JFrame with Panel");

  JComboBox packageChoice = new JComboBox();
  packageChoice.addItem("A+ Certification");
  packageChoice.addItem("Network+ Certification ");
  packageChoice.addItem("Security+ Certifictation");
  packageChoice.addItem("CIT Full Test Package");

  packageChoice.addActionListener(this);

  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  JPanel pane = new JPanel();
  pane.add(button);
  pane.add(packageChoice);
  setContentPane(pane);
  setSize(200,100);
  setVisible(true);

 }
}

then later

public class CreateJFrameWithPanel
{
 public static void main(String[] args)
 {
  JFrameWithPanel panel = new JFrameWithPanel();
 }
}