У меня есть основной фрейм, где я хочу отобразить объект моего класса NewUser в центральном положении, используя макет карты. Вот мой основной класс

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



public class CardLayoutDemo implements ItemListener {
JPanel cards; //a panel that uses CardLayout
final static String BUTTONPANEL = "Card with JButtons";
final static String TEXTPANEL = "Card with JTextField";

public void addComponentToPane(Container pane) {
    //Put the JComboBox in a JPanel to get a nicer look.
    JPanel comboBoxPane = new JPanel(); //use FlowLayout
    String comboBoxItems[] = { BUTTONPANEL, TEXTPANEL };
    JComboBox cb = new JComboBox(comboBoxItems);
    cb.setEditable(false);
    cb.addItemListener(this);
    comboBoxPane.add(cb);

    //Create the "cards".
    NewUser newUser = new NewUser();

    JPanel card1 = new JPanel();
    card1.add(new JButton("Button 1"));
    card1.add(new JButton("Button 2"));
    card1.add(new JButton("Button 3"));

    JPanel card2 = new NewUser();


    //Create the panel that contains the "cards".
    cards = new JPanel(new CardLayout());
    cards.add(card1, BUTTONPANEL);
    cards.add(card2, TEXTPANEL);

    pane.add(comboBoxPane, BorderLayout.PAGE_START);
    pane.add(cards, BorderLayout.CENTER);
}

public void itemStateChanged(ItemEvent evt) {
    CardLayout cl = (CardLayout)(cards.getLayout());
    cl.show(cards, (String)evt.getItem());
}

/**
 * Create the GUI and show it.  For thread safety,
 * this method should be invoked from the
 * event dispatch thread.
 */
private static void createAndShowGUI() {
    //Create and set up the window.
    JFrame frame = new JFrame("CardLayoutDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    CardLayoutDemo demo = new CardLayoutDemo();
    demo.addComponentToPane(frame.getContentPane());

    //Display the window.
    frame.pack();
    frame.setVisible(true);
}

public static void main(String[] args) {
    /* Use an appropriate Look and Feel */
    try {
        //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
    } catch (UnsupportedLookAndFeelException ex) {
        ex.printStackTrace();
    } catch (IllegalAccessException ex) {
        ex.printStackTrace();
    } catch (InstantiationException ex) {
        ex.printStackTrace();
    } catch (ClassNotFoundException ex) {
        ex.printStackTrace();
    }
    /* Turn off metal's use of bold fonts */
    UIManager.put("swing.boldMetal", Boolean.FALSE);

    //Schedule a job for the event dispatch thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
    });
}
}

Вот мой класс NewUser

import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class NewUser extends JPanel {

private static final long serialVersionUID = 1L;
private JLabel lblUsername, lblPassword, lblConfirmMsg;
private JPasswordField txtPassword, txtCPassword;
private JTextField txtUsername, txtName;
private JButton btnSave, btnCancel;
JPanel panelNewUser;

Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();

public NewUser() {

    this.setSize(350, 270);
    this.setLocation((screen.width - 500) / 2, ((screen.height - 350) / 2));
    this.setLayout(null);
    panelNewUser= this;
    lblUsername = new JLabel("Username");
    lblPassword = new JLabel("Password");
    lblConfirmMsg = new JLabel("Re-enter Password");
    txtName = new JTextField();

    txtUsername = new JTextField();
    txtPassword = new JPasswordField();
    txtCPassword = new JPasswordField();
    btnSave = new JButton("Save");
    btnCancel = new JButton("Cancel");

    lblUsername.setBounds(30, 30, 100, 25);
    this.add(lblUsername);
    txtUsername.setBounds(150, 30, 150, 25);
    this.add(txtUsername);
    lblPassword.setBounds(30, 70, 100, 25);
    this.add(lblPassword);
    txtPassword.setBounds(150, 70, 150, 25);
    this.add(txtPassword);
    lblConfirmMsg.setBounds(30, 110, 110, 25);
    this.add(lblConfirmMsg);
    txtCPassword.setBounds(150, 110, 150, 25);
    this.add(txtCPassword);
    btnSave.setBounds(60, 155, 100, 25);
    this.add(btnSave);
    btnCancel.setBounds(180, 155, 100, 25);
    this.add(btnCancel);

    txtName.addKeyListener(new KeyAdapter() {

        public void keyTyped(KeyEvent e) {
            char c = e.getKeyChar();
            if (!(Character.isLetter(c) || (c == KeyEvent.VK_BACK_SPACE)
                    || (c == KeyEvent.VK_SPACE) || (c == KeyEvent.VK_DELETE))) {
                getToolkit().beep();
                JOptionPane.showMessageDialog(null, "Invalid Character",
                        "ERROR", JOptionPane.ERROR_MESSAGE);
                e.consume();
            }
        }
    });
    txtUsername.addKeyListener(new KeyAdapter() {

        public void keyTyped(KeyEvent e) {
            char c = e.getKeyChar();
            if (!(Character.isLetter(c) || (c == KeyEvent.VK_BACK_SPACE)
                    || (Character.isDigit(c)) || (c == KeyEvent.VK_DELETE))) {
                getToolkit().beep();
                JOptionPane.showMessageDialog(null, "Invalid Character",
                        "ERROR", JOptionPane.ERROR_MESSAGE);
                e.consume();
            }
        }
    });
    btnCancel.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(ActionEvent e) {
            resetField();
            panelNewUser.setVisible(false);
        System.out.println("hello");
        }
    });
    btnSave.addActionListener(new java.awt.event.ActionListener() {


        public void actionPerformed(ActionEvent e) {

            //DatabaseHelper databaseHelper = new DatabaseHelper();
            if (txtUsername.getText() == null
                    || txtUsername.getText().equals("")) {
                JOptionPane.showMessageDialog(null, "Enter Username",
                        "Missing fields", JOptionPane.DEFAULT_OPTION);
                txtUsername.requestFocus();
                return;
            }
            if (txtPassword.getPassword() == null
                    || txtPassword.getPassword().equals("")) {
                JOptionPane.showMessageDialog(null, "Enter Password",
                        "Missing fields", JOptionPane.DEFAULT_OPTION);
                txtPassword.requestFocus();
                return;
            }
            if (txtCPassword.getPassword() == null
                    || txtCPassword.getPassword().equals("")) {
                JOptionPane.showMessageDialog(null,
                        "Confirm your password", "Missing fields",
                        JOptionPane.DEFAULT_OPTION);
                txtCPassword.requestFocus();
                return;
            }
            if (!txtPassword.getText()
                    .equals(txtPassword.getText())) {
                JOptionPane.showMessageDialog(null,
                        "Passwords do not match.", "ERROR",
                        JOptionPane.DEFAULT_OPTION);
                txtCPassword.requestFocus();
                return;
            }


                if (true) {
                    JOptionPane.showMessageDialog(null,
                            "A new user is created", "SUCCESS",
                            JOptionPane.DEFAULT_OPTION);
                    resetField();
                }


        }
    });

    }// constructor closed

//action listener


public void resetField()
{

    txtUsername.setText("");
    txtCPassword.setText("");
    txtPassword.setText("");
}
}// class closed

Я хочу, чтобы объект NewUser отображался в центральной позиции основного класса