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is the method to create simple login wrong

I am a newbie in Java GUI development and I am stuck in the following code.
I am open to suggestions. I am actually trying to create a simple login that gives OK if the password is matched to the number 3124, and otherwise shows the error message. Please help me.
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTextField;
public class testing {
private JFrame frame;
private JTextField username;
private JTextField password;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
testing window = new testing();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public testing() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 450, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
JButton btnNewButton_1 = new JButton("cancel");
btnNewButton_1.setBounds(266, 181, 109, 56);
frame.getContentPane().add(btnNewButton_1);
username = new JTextField();
username.setBounds(227, 11, 128, 39);
frame.getContentPane().add(username);
username.setColumns(10);
password = new JTextField();
password.setBounds(227, 76, 128, 39);
frame.getContentPane().add(password);
final int num;
num=Integer.parseInt(password);
password.setColumns(10);
JButton btnNewButton = new JButton("login");
btnNewButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(num==3124)
{JOptionPane.showMessageDialog(null, "correct");}
else
{JOptionPane.showMessageDialog(null, "wrong");}
}
});
btnNewButton.setBounds(62, 181, 123, 56);
frame.getContentPane().add(btnNewButton);
}
}

You were checking the password even before the user has had the chance to enter anything into the text box. You need to get and check the value of num in the event listener code i.e. in actionPerformed. Also, don't convert the password to int (someone may enter some non-numeric string).
This code below works better.
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import javax.swing.JTextField;
public class Testing {
private JFrame frame;
private JTextField username;
private JTextField password;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Testing window = new Testing();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public Testing() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 450, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
JButton btnNewButton_1 = new JButton("cancel");
btnNewButton_1.setBounds(266, 181, 109, 56);
frame.getContentPane().add(btnNewButton_1);
username = new JTextField();
username.setBounds(227, 11, 128, 39);
frame.getContentPane().add(username);
username.setColumns(10);
password = new JTextField();
password.setBounds(227, 76, 128, 39);
frame.getContentPane().add(password);
password.setColumns(10);
JButton btnNewButton = new JButton("login");
btnNewButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
final String num;
num = (password.getText());
if (num.equalsIgnoreCase("3124")) {
JOptionPane.showMessageDialog(null, "correct");
} else {
JOptionPane.showMessageDialog(null, "wrong");
}
}
});
btnNewButton.setBounds(62, 181, 123, 56);
frame.getContentPane().add(btnNewButton);
}
}

random number generator jframe

Working on a side project for a professor that wants a random number generator.
The program in its current state leaves a lot to be desired but I think I'm on the right track. However, I am stuck when it comes to using the text field, passing that data to my random number equation, and displaying it. Basically, the program isn't waiting for the user input to the text field.
We never made it past OOP in school so I need to pull out the big guns (you guys).
Here is what I am working with currently. The last bit at the end is the part that I am having issue with.
package RandomButton;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.util.Random;
import java.util.Scanner;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JButton;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.JLabel;
public class GUI extends JFrame {
private JPanel contentPane;
private JTextField textField;
private JTextField ClassSize;
private JLabel label;
private JTextField textField_1;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
GUI frame = new GUI();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public GUI() {
int x;
int max;
String strMax;
String strX;
Scanner kb = new Scanner(System.in);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
//Text field code
textField = new JTextField();
textField.setText("1");
textField.setHorizontalAlignment(SwingConstants.CENTER);
textField.setBounds(10, 143, 414, 35);
contentPane.add(textField);
textField.setColumns(10);
//Randomize button code
JButton btnNewButton = new JButton("Randomize!");
btnNewButton.setFont(new Font("Tahoma", Font.BOLD, 40));
btnNewButton.setBounds(10, 196, 414, 54);
contentPane.add(btnNewButton);
//Label code
label = new JLabel();
label.setFont(new Font("Tahoma", Font.PLAIN, 70));
label.setHorizontalAlignment(SwingConstants.CENTER);
label.setBounds(10, 11, 414, 103);
contentPane.add(label);
//math code
Random num = new Random();
strMax = textField.getText();
max = Integer.parseInt(strMax);
x = num.nextInt(max) + 1;
strX = String.valueOf(x);
label.setText(strX);
}
}

What you need is to add an ActionListener, see javadoc here
Simple modification of the code, without bigger discussion, is to move up the code that simulate random numbers...
//Randomize button code
JButton btnNewButton = new JButton("Randomize!");
btnNewButton.setFont(new Font("Tahoma", Font.BOLD, 40));
btnNewButton.setBounds(10, 196, 414, 54);
contentPane.add(btnNewButton);
// the listener
btnNewButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Random num = new Random();
String strMax = textField.getText();
int max = Integer.parseInt(strMax);
int x = num.nextInt(max) + 1;
String strX = String.valueOf(x);
label.setText(strX);
}
} );

How can activate another gui class with JButton

I have two GUI classes named Menu and convert. I want to run the convert class when I click the "open" button. It looks so simple, but I couldn't figure it out.
Menu class
package com.ui;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Menu {
private JFrame frame;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Menu window = new Menu();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public Menu() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 450, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton btnConvert = new JButton("open");
btnConvert.setBounds(44, 52, 89, 23);
btnConvert.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
//???
}
});
frame.getContentPane().setLayout(null);
frame.getContentPane().add(btnConvert);
}
}
convert class
package com.ui;
import java.awt.EventQueue;
import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.border.TitledBorder;
import java.awt.Color;
import javax.swing.JComboBox;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class convert {
private JFrame frmTitle;
private JTextField textField;
private double value;
private ButtonGroup group;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
convert window = new convert();
window.frmTitle.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public convert() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frmTitle = new JFrame();
frmTitle.setTitle("TITLE");
frmTitle.setBounds(100, 100, 450, 300);
frmTitle.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frmTitle.getContentPane().setLayout(null);
JLabel lblInputValue = new JLabel("Input value:");
lblInputValue.setBounds(29, 22, 79, 14);
frmTitle.getContentPane().add(lblInputValue);
textField = new JTextField();
textField.setBounds(22, 47, 86, 20);
frmTitle.getContentPane().add(textField);
textField.setColumns(10);
JPanel panel = new JPanel();
panel.setBorder(new TitledBorder(null, "Convert", TitledBorder.LEADING, TitledBorder.TOP, null, Color.RED));
panel.setBounds(29, 118, 264, 133);
frmTitle.getContentPane().add(panel);
panel.setLayout(null);
final JRadioButton rdbtnKelvin = new JRadioButton("Kelvin");
rdbtnKelvin.setBounds(6, 30, 67, 23);
panel.add(rdbtnKelvin);
final JRadioButton rdbtnFahrenheit = new JRadioButton("Fahrenheit");
rdbtnFahrenheit.setBounds(71, 30, 77, 23);
panel.add(rdbtnFahrenheit);
final JRadioButton rdbtnCelcius = new JRadioButton("Celcius");
rdbtnCelcius.setBounds(174, 30, 67, 23);
panel.add(rdbtnCelcius);
group = new ButtonGroup();
group.add(rdbtnCelcius);
group.add(rdbtnFahrenheit);
group.add(rdbtnKelvin);
final JComboBox comboBox = new JComboBox();
comboBox.setModel(new DefaultComboBoxModel(new String[] {"Celcius", "Fahrenheit", "Kelvin"}));
comboBox.setBounds(177, 47, 116, 20);
frmTitle.getContentPane().add(comboBox);
JButton btnConvert = new JButton("CONVERT");
btnConvert.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
value = Double.parseDouble(textField.getText().toString());
if(comboBox.getSelectedItem().toString().equals("Celcius")){
if(rdbtnCelcius.isSelected()==true){
value = value;
}
else if (rdbtnFahrenheit.isSelected()==true){
value= 1.8*value +32;
}
else{
value =value+273;
}
}
else if (comboBox.getSelectedItem().toString().equals("Fahrenheit")){
if(rdbtnFahrenheit.isSelected()==true){
value = value;
}
else if (rdbtnCelcius.isSelected()==true){
value= (value-32)*1.8;
}
else{
value =(value-32)/1.8+273;
}
}
else{
if(rdbtnCelcius.isSelected()==true){
value = value-273;
}
else if (rdbtnFahrenheit.isSelected()==true){
value= value -273*1.8+32;
}
else{
value =value;
}
}
textField.setText(value +"");
textField.setEnabled(false);
}
});
btnConvert.setBounds(303, 114, 89, 23);
frmTitle.getContentPane().add(btnConvert);
JButton btnClear = new JButton("CLEAR");
btnClear.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText("");
textField.setEnabled(true);
comboBox.setSelectedIndex(0);
rdbtnKelvin.setSelected(true);
}
});
btnClear.setBounds(303, 170, 89, 23);
frmTitle.getContentPane().add(btnClear);
}
}

First of all, class names and constructors should start with an upper case letter, like you did it for class Menu, but not for class convert.
A Java programm should have just one and only one main method for all classes. So, delete complete your main method from Convert class, put new Convert(); in the actionPerformed() method of btnConvert in Menu class:
btnConvert.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
new Convert();
}
});
and add frmTitle.setVisible(true); to the end of the initialize() method of Convert class.

First, your class names should begin with a capital letter, so instead of "convert" it should be "Convert.
Create a public method in Convert:
public JFrame getFrame() {
return frmTitle;
}
Then in your button's actionPerformed() method, just:
Convert w = new Convert();
w.getFrame().setVisible(true);

AWT-EventQueue-0" StackOverflowError

Afternoon all, i have a problem with some JFrame code, this JFrame is started when the user presses "New User", and whenever they do so, i get:
Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
at frontend.Registration.<init>(Registration.java:36)
at frontend.Registration.<init>(Registration.java:25)
at frontend.Registration.<init>(Registration.java:25)
at frontend.Registration.<init>(Registration.java:25)
With this code:
package frontend;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.SQLException;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;
public class Registration extends JFrame {
/**
*
*/
private static final long serialVersionUID = 1L;
private static boolean ranOnce = false;
private JPanel contentPane;
private Registration reg = new Registration();
private JTextField userTF;
private JTextField passTF;
private JTextField emailTF;
private LoginProcess lp = new LoginProcess();
private JLabel error;
/**
* Create the frame.
*/
public Registration() {
if (!ranOnce) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
ranOnce = true;
reg = new Registration();
reg.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 245, 195);
setLocationRelativeTo(null);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JLabel lblUsername = new JLabel("Username:");
lblUsername.setBounds(10, 11, 75, 14);
contentPane.add(lblUsername);
JLabel lblPassword = new JLabel("Password:");
lblPassword.setBounds(10, 36, 75, 14);
contentPane.add(lblPassword);
JLabel lblEmail = new JLabel("Email:");
lblEmail.setBounds(10, 61, 75, 14);
contentPane.add(lblEmail);
userTF = new JTextField();
userTF.setBounds(95, 8, 130, 20);
contentPane.add(userTF);
userTF.setColumns(10);
passTF = new JTextField();
passTF.setColumns(10);
passTF.setBounds(95, 33, 130, 20);
contentPane.add(passTF);
emailTF = new JTextField();
emailTF.setColumns(10);
emailTF.setBounds(95, 58, 130, 20);
contentPane.add(emailTF);
error = new JLabel("Error: Username already in use");
error.setBounds(10, 120, 215, 14);
contentPane.add(error);
JButton regBtn = new JButton("Register");
regBtn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
try {
if (lp.newUser(userTF.getText(), passTF.getText(), emailTF.getText())) {
reg.setVisible(false);
Main.mainFrame.setVisible(true);
} else {
if (lp.duplicateAccount) {
error.setText("lol");
}
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
regBtn.setBounds(10, 86, 215, 23);
contentPane.add(regBtn);
}
}
I know this error is caused by an infinite loop, or something. but i have a boolean in place to stop it from infinitely running. This code was working about 20mins ago, and i haven't changed the first part of the constructor since i created the code.
Any ideas? Thanks..

You create a new Object in the line private Registration reg = new Registration();.
You should create this object in the consturctor.

The problem at that line:
private Registration reg = new Registration();
You get in a infinite loop and then stack overflow.

NullPointException error when setting attributes

I'm getting a NullPointerException error at line 77 lblNewLabel.setVisible(false);
which is called from line 65 runTest(); in the following code. (This is a dummy project I wrote to simulate a problem I'm having in a larger project). What I'm trying to do is change the attribute of several fields, buttons, etc based on user action at various places in the project. I would like to group all the changes in a separate method that can be called from various other methods. I'm still a Java novice, having come from some Visual Basic and Pascal experience. Seems like what I'm trying to do should be straight forward, but for now, I'm at a loss. Thanks in advance for your suggestions.
package woodruff;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.SwingConstants;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTextField;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
public class MyTest extends JFrame {
private JPanel contentPane;
private JTextField txtHasFocus;
private JLabel lblNewLabel;
/**
* Create the frame.
*/
public MyTest() {
initialize();
}
private void initialize() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 237, 161);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
final JLabel lblNewLabel = new JLabel("This is a label.");
lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
lblNewLabel.setHorizontalTextPosition(SwingConstants.CENTER);
lblNewLabel.setBounds(10, 25, 202, 14);
contentPane.add(lblNewLabel);
JButton btnShow = new JButton("Show");
btnShow.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
lblNewLabel.setVisible(true);
}
});
btnShow.setBounds(10, 50, 89, 23);
contentPane.add(btnShow);
JButton btnHide = new JButton("Hide");
btnHide.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
lblNewLabel.setVisible(false);
}
});
btnHide.setBounds(123, 50, 89, 23);
contentPane.add(btnHide);
txtHasFocus = new JTextField();
txtHasFocus.addFocusListener(new FocusAdapter() {
#Override
public void focusGained(FocusEvent arg0) {
// Following results in NullPointerException error
// at woodruff.MyTest.runTest(MyTest.java:77)
runTest();
}
});
txtHasFocus.setHorizontalAlignment(SwingConstants.CENTER);
txtHasFocus.setText("Has Focus?");
txtHasFocus.setBounds(67, 92, 86, 20);
contentPane.add(txtHasFocus);
txtHasFocus.setColumns(10);
}
private void runTest() {
lblNewLabel.setVisible(false);
}
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
MyTest frame = new MyTest();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
}

In the initialize() method, you have created a local variable for JLabel, and hence are not initializing the instance field, as a reason it remains initialized to null, and hence NPE.
final JLabel lblNewLabel = new JLabel("This is a label.");
change the above line to: -
lblNewLabel = new JLabel("This is a label.");