GUI Swing

package net.codejava.swing.jpanel;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.PopupMenu;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.border.EmptyBorder;


public class SwingJPanelDemo extends JFrame {

    private JLabel labelUsername = new JLabel("Vardas");
    private JLabel labelPassword = new JLabel("Pinigu kiekis");
    private JTextField textUsername = new JTextField(20);
    private JTextField fieldPassword = new JTextField(8);
    private JButton myButton = new JButton("Prisijungti");
    String Vardas = "";
    int Suma;

    public SwingJPanelDemo() {
        super("Zaidimas");

        // create a new panel with GridBagLayout manager
        JPanel newPanel = new JPanel(new GridBagLayout());
        JPanel newPanel1 = new JPanel();

        newPanel1.setBounds(100, 100, 150, 75);
        newPanel1.setVisible(true);


        GridBagConstraints constraints = new GridBagConstraints();
        constraints.anchor = GridBagConstraints.WEST;
        constraints.insets = new Insets(10, 10, 10, 10);

        // add components to the panel
        constraints.gridx = 0;
        constraints.gridy = 0;
        newPanel.add(labelUsername, constraints);

        constraints.gridx = 1;
        newPanel.add(textUsername, constraints);

        constraints.gridx = 0;
        constraints.gridy = 1;
        newPanel.add(labelPassword, constraints);

        constraints.gridx = 1;
        newPanel.add(fieldPassword, constraints);

        constraints.gridx = 0;
        constraints.gridy = 2;
        constraints.gridwidth = 2;
        constraints.anchor = GridBagConstraints.CENTER;
        newPanel.add(myButton, constraints);

        // set border for the panel
        newPanel.setBorder(BorderFactory.createTitledBorder(
                BorderFactory.createEtchedBorder(), "Sveiki atvyke"));

        // add the panel to this frame

        add(newPanel);



        pack();
        setLocationRelativeTo(null);


        myButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
        {

            try{
       Vardas =  textUsername.getText();
       Suma = Integer.parseInt(fieldPassword.getText());


       if(Suma<0){
           System.out.println("Skaicius yra neigiamas prašome pabandyti iš naujo ");
           JOptionPane.showMessageDialog(null,"Skaicius yra neigiamas prašome pabandyti iš naujo ");
           Suma = 0;
           Suma = Integer.parseInt(fieldPassword.getText());





       }
       if(Suma>0){

           System.out.println(Vardas+" " +Suma);
           JOptionPane.showMessageDialog(null, "Žaidejo vardas: " + Vardas +  " \n" + "Suma žaidejas žaidžia: " + Suma + "$");

           newPanel.setVisible(false);
           add(newPanel1);

       }
            }
             catch (Exception  ee) {

          JOptionPane.showMessageDialog(null,"Neteisingai įvestas skaičius prašome pabandyti iš naujo");
      }
        }
});



       }





    public static void main(String[] args) {
        // set look and feel to the system look and feel
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new SwingJPanelDemo().setVisible(true);
            }
        });
    }
}