Problem in displaying loginpage when user press logout

Question

Hi everyone, I am new to Swing and facing an issue which might appear simple to you people.
I have a Login Screen. When user supply credentials and press the login button, the next page is displayed which has a logout button. If user clicks this logout button, ideally the login screen should come. I am struck up in implementing this functionallity. I'm attached SAMPLE Code for the same.
// MainFrame.java
import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.io.PrintStream;
import java.text.SimpleDateFormat;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class MainFrame extends JFrame implements WindowListener{
    private static final long serialVersionUID = 1L;
     public static  String server_url = "t3://localhost:7001";
     public static  String JNDI_NAME = "com.qwest.bpm.designerserver.DesignerServerRemoteHome";
     static final String title_base = "MY App";
     PrintStream log;
     SimpleDateFormat df;
     public static JPanel current_page;
    String errmsg;
    public Color background;
    public Color color_tablehead;
    public Color color_canvas;
    Font font_textfield;
    String database;
    MainFrame(String title){
         super(title);
        System.setSecurityManager(null);
        setSize(900, 720);
          addWindowListener(this);
          rootPane.setDoubleBuffered(false);
          background = new Color(0.9f,0.9f,0.7f);
          color_tablehead = new Color(0.8f,0.8f,0.6f);
          color_canvas = new Color(0.97f,1.0f,0.97f);
          font_textfield = new Font("courier", Font.PLAIN, 12);
          setBackground(background);
          getContentPane().setBackground(null);
          log = System.out;
          df = new SimpleDateFormat("HH:mm:ss");
          setDefaultLookAndFeelDecorated(true);
        errmsg = null;
        database = "Oracle";
     public void setPage(JPanel page) {
          if (current_page!=null) current_page.setVisible(false);
          Container content_pane = getContentPane();
          if (!content_pane.isAncestorOf(page)) {
               // System.out.println("Add page " + page.getClass().getName());
               content_pane.add(page);
          page.setVisible(true);
          current_page = page;
        if (errmsg!=null) {
            JOptionPane.showMessageDialog(this, errmsg);
            errmsg = null;
     public void logout() {
          //Code to be changed here
       System.exit(0);
     public static void main(String[] args){
          MainFrame frame = new MainFrame("My App");
          frame.setPage(LoginPage.getPage(frame));
          frame.setVisible(true);
     public void windowActivated(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowClosed(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowClosing(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowDeactivated(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowDeiconified(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowIconified(WindowEvent e) {
          // TODO Auto-generated method stub
     public void windowOpened(WindowEvent e) {
          // TODO Auto-generated method stub
//MainPanel.java
import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.JPanel;
public class MainPanel extends JPanel{
     public MainFrame frame;
     protected Color background;
     public MainPanel(MainFrame frame) {
          super();
          this.frame = frame;
          setLayout(new BorderLayout());
          setBackground(null);
//LoginPage.java
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.AbstractButton;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
public class LoginPage extends MainPanel implements ActionListener {
     private static final long serialVersionUID = 1L;
     JTextField username, serverurl, servername;
     JPasswordField password;
     static LoginPage singleton = null;
     LoginPage(MainFrame frame) {
          super(frame);
          setLayout(null);
          JLabel label;
          JPanel panel = new JPanel(new GridLayout(2,2));
        panel.setLayout(null);
        panel.setBounds(100,100,200,200);
        panel.setBorder(BorderFactory.createTitledBorder("Credentials "));
        panel.setSize(600,350);
        panel.setOpaque(false);
          label = new JLabel("User Name");
          label.setBounds(60, 60, 120, 20);
          panel.add(label);
          username = new JTextField();
          username.setBounds(200, 60, 120, 20);
        //username.setActionCommand(C.ACTION_LOGIN);
          panel.add(username);
          label = new JLabel("Password");
          label.setBounds(60, 90, 120, 20);
          panel.add(label);
          password = new JPasswordField();
          password.setBounds(200, 90, 120, 20);
        password.setActionCommand("login");
        password.addActionListener(this);
          panel.add(password);
          JButton button_login = new JButton("Log In");
          button_login.setBounds(150, 240, 120, 25);
          button_login.setBackground(background);
          button_login.setActionCommand("login");
          button_login.addActionListener(this);
          panel.add(button_login);
        add(panel);
     static LoginPage getPage(MainFrame frame) {
          if (singleton==null)
               singleton = new LoginPage(frame);
          return singleton;
     public void actionPerformed(ActionEvent e) {
         Object source = e.getSource();
         String cmd;
          if (source instanceof AbstractButton)
               cmd = ((AbstractButton)source).getActionCommand();
        else if (source instanceof JPasswordField)
            cmd = "login";  
          else return;
          if(cmd.equalsIgnoreCase("login")) {
               frame.setPage(NextPage.getPage(frame));
//NextPage.java
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.AbstractButton;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
public class NextPage extends MainPanel implements ActionListener{
     private static final long serialVersionUID = 1L;
     JTextField username, serverurl, servername;
     JPasswordField password;
     static NextPage singleton = null;
     NextPage(MainFrame frame) {
          super(frame);
          setLayout(null);
          JLabel label;
          JPanel panel = new JPanel(new GridLayout(2,2));
        panel.setLayout(null);
        panel.setBounds(100,100,200,200);
        panel.setBorder(BorderFactory.createTitledBorder("Credentials "));
        panel.setSize(600,350);
        panel.setOpaque(false);
          label = new JLabel(" Hurray Login Successfull ");
          label.setBounds(60, 60, 120, 20);
          panel.add(label);
          username = new JTextField();
          username.setBounds(200, 60, 120, 20);
        //username.setActionCommand(C.ACTION_LOGIN);
          panel.add(username);
          label = new JLabel("Now try Logout ");
          label.setBounds(60, 90, 120, 20);
          panel.add(label);
          JButton button_login = new JButton("Log Out");
          button_login.setBounds(150, 240, 120, 25);
          button_login.setBackground(background);
          button_login.setActionCommand("logout");
          button_login.addActionListener(this);
          panel.add(button_login);
        add(panel);
     static NextPage getPage(MainFrame frame) {
          if (singleton==null)
               singleton = new NextPage(frame);
          return singleton;
     public void actionPerformed(ActionEvent e) {
         Object source = e.getSource();
         String cmd ="";
          if (source instanceof AbstractButton)
               cmd = ((AbstractButton)source).getActionCommand();
          if(cmd.equalsIgnoreCase("logout")) {
               frame.logout();
}

Answer 1

solved it :)