Program Java : Membuat Check Box dengan GUI di Java

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

public class TestCheck extends JFrame implements ActionListener
{
JPanel pnlCheck = new JPanel();
JCheckBox haveCC = new JCheckBox("Membaca");
JCheckBox haveDD = new JCheckBox("Nonton Naruto");
JButton btnShow = new JButton("Show");

public TestCheck()
{
//SET CHECK
pnlCheck.setLayout(new FlowLayout());

pnlCheck.add(haveCC);
pnlCheck.add(haveDD);
pnlCheck.add(btnShow);
btnShow.addActionListener(this);

setLayout(new FlowLayout());
add(pnlCheck);

setDefaultCloseOperation(EXIT_ON_CLOSE);
setTitle("Test Combobox");
setBounds(0,0,350,150);
}


public static void main(String[] args){
TestCheck theApp = new TestCheck();
theApp.setVisible(true);
}

public void actionPerformed(ActionEvent e){
String str = "";
if(haveCC.isSelected()) str +="1.Membaca \n";
else str +="";
if(haveDD.isSelected()) str +="2.Nonton Naruto\n";
else str +="";
JOptionPane.showMessageDialog(this,str);
}
}