Positioning component inside card layout

I have a main frame where i want to display object of my NewUser class in center position using card layout.Here is my main class

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();
        }
    });
}
}

Here is my NewUser class

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

I want the object of NewUser to be displayed at center position in main class

Welcome to the wounderful world of Graphical User Interface Design, where the size of the font, the screen resolution and the DPI you develop your mind blowingly awesome UI on, won't ever match that of the end user...

Now, you have two choices. Spend the rest of your life trying to meet every weird edge case that comes up, in the process re-inventing the wheel, a wheel that has been made available for you in the guise of the layout managers (sorry if sound fictitious, but most people's problems in Swing could be solved by understanding layout managers :P).

You might like to have a read through Using Layout Managers and A Visual Guide to Layout Managers

public class TestLayout02 {

    public static void main(String[] args) {
        new TestLayout02();
    }

    public TestLayout02() {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                /* 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.
                createAndShowGUI();
            }
        });
    }

    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.
     */
    protected 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 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);

            setLayout(new GridBagLayout());

            panelNewUser = this;
            lblUsername = new JLabel("Username");
            lblPassword = new JLabel("Password");
            lblConfirmMsg = new JLabel("Re-enter Password");
            txtName = new JTextField();

            txtUsername = new JTextField(12);
            txtPassword = new JPasswordField(12);
            txtCPassword = new JPasswordField(12);
            btnSave = new JButton("Save");
            btnCancel = new JButton("Cancel");

            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.insets = new Insets(2, 2, 2, 2);
            gbc.anchor = GridBagConstraints.WEST;

//            lblUsername.setBounds(30, 30, 100, 25);
            this.add(lblUsername, gbc);
//            txtUsername.setBounds(150, 30, 150, 25);
            gbc.gridx++;
            this.add(txtUsername, gbc);
//            lblPassword.setBounds(30, 70, 100, 25);
            gbc.gridx = 0;
            gbc.gridy++;
            this.add(lblPassword, gbc);
//            txtPassword.setBounds(150, 70, 150, 25);
            gbc.gridx++;
            this.add(txtPassword, gbc);
//            lblConfirmMsg.setBounds(30, 110, 110, 25);
            gbc.gridx = 0;
            gbc.gridy++;
            this.add(lblConfirmMsg, gbc);
//            txtCPassword.setBounds(150, 110, 150, 25);
            gbc.gridx++;
            this.add(txtCPassword, gbc);
//            btnSave.setBounds(60, 155, 100, 25);
            gbc.gridx = 0;
            gbc.gridy++;
            gbc.anchor = GridBagConstraints.CENTER;
            this.add(btnSave, gbc);
//            btnCancel.setBounds(180, 155, 100, 25);
            gbc.gridx++;
            this.add(btnCancel, gbc);

            // This is a bad idea, use a DocumentFilter
            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();
                    }
                }
            });
            // This is a bad idea, use a DocumentFilter
            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
}

You may also like to have a read through DocumentFilter.

If you prefer to do it manually, you need to attach a ComponentListener and monitor the componentResized event and re-layout all your components again.

You'll also want to look at the FontMetrics so you can properly take into account the differences in the font size between systems...