public class checkUsernames extends JFrame {
private static JTextArea textArea1;
private static JButton button1;
private static JScrollPane scrollPane1;
private static JTextField textField1;
private static JPasswordField passwordField1;
private static JLabel label3;
private static JButton button2;
private static JLabel label1;
private static JLabel label2;
public checkUsernames() {
initComponents();
}
public static void main(String[] args) throws IOException {
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
} catch (Exception e) {
JOptionPane.showMessageDialog(null, "Nimbus isn't available");
}
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
checkUsernames GUI = new checkUsernames();
GUI.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
GUI.setVisible(true);
}
});
String username = textField1.toString();
String password = passwordField1.toString();
Exception in thread "main" java.lang.NullPointerException
checkUsernames is the only class. When I try to run the application the program executes further (proceeding without String username & String password) without waiting for input. How can I fix this?
If you want the code execution to stop while waiting for input, make the JFrame a modal JDialog or JOptionPane instead.
Well invokeLater will invoke the code later. It dosent gurantee textfield1.toString() to execute after checkUserNames()
None of your private static members appear to be initialized at all. You won't get past the NullPointerException until you initialize each and every object you create before you use it.
I have no idea what you're talking about. You have to do something like this for all those objects:
private static JTextArea textArea1 = new JTextArea();
You aren't entering a username or password; you're creating a text area UI element that can accept them when you do enter them.
Why dont you use SwingUtilities.invokeAndWait() instead? This seems to solve your problem immediately.
Here is the simple example:
import javax.swing.SwingUtilities;
public class InvokeAndWaitExample {
public static void main (String[] args) {
try {
SwingUtilities.invokeAndWait(new Runnable () {
public void run () {
System.out.println("Hello World on " + Thread.currentThread());
}
});
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("Finished on " + Thread.currentThread());
}
}
Related
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 7 years ago.
I'm relatively new to Java and I am trying to make a login page for my desktop application. I have a thread called "listen" that should be called when the application first opens, its job is to check weather the username and password fields are not blank.
public class Login extends JFrame implements Runnable {
private JPanel contentPane;
private JTextField txtUsername;
private JPasswordField pwdPassword;
private JLabel lblUsername;
private JButton btnLogin;
private JLabel lblPassword;
private JCheckBox cboxRemember;
private Thread run, listen;
private boolean running = true;
public Login() {
createWindow();
run = new Thread(this, "Running");
running = true;
run.start();
}
private void createWindow() {
//application layout and actionListener for login button
}
public void run() {
listen();
}
public void listen() {
listen = new Thread("Listen") {
public void run() {
while (running) {
if (txtUsername.getText().equals("") || pwdPassword.getText().equals("")) btnLogin.setEnabled(false);
else btnLogin.setEnabled(true);
}
}
};
listen.start();
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Login frame = new Login();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
}
Whenever i try to execute my code the 'listen' thread throws a NullPointerException on this line if (txtUsername.getText().equals("") || pwdPassword.getText().equals("")) btnLogin.setEnabled(false); I'm not sure what am I doing wrong, any help will be appreciated, thanks.
Initialize your txtUserName and pwdPassword:
txtUsername = new JTextField();
pwdPassword = new JPasswordField();
Hope this helps.
I think you're if{} block gets executed before any initialization. Add
if (txtUsername.getText()!=null &&( txtUsername.getText().equals("") || pwdPassword.getText().equals("")))
Since txtUsername and pwdPassword have not been initialized, you will get a NPE in your IF{} statement.
package test2;
public class NewJFrame extends javax.swing.JFrame {
private static void valueGen(javax.swing.JTextField jTextField1) {
String x = jTextField1.getText();
System.out.println(x);
}
public NewJFrame() {
initComponents();
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt){
jTextField1.setText("Hello");
}
private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {
}
public javax.swing.JTextField getTextField() {
jTextField1.getText();
return this.jTextField1;
}
public static void main(String args[]) {
NewJFrame myFrame = new NewJFrame();
valueGen(myFrame.getTextField());
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new NewJFrame().setVisible(true);
}
});
}
private javax.swing.JButton jButton1;
private javax.swing.JTextField jTextField1;
}
I have a program as shown above. I need to set the text "hello" in a text field when the submit button is clicked. It works. But then i need to use that text in a function called valueGen where it is printed. But the text doesn't get printed by executing the above code. What is wrong with this code?
It's unorganized. Always put class variables at the top.
Like Cool Guy said, put myFrame instead of new NewJTest()
valueGen is actually being called before you can click the button. Put it in the jTextField1ActionPerformed; that might fix it.
In netbeans out put of the System.out.println(); will be displayed in the output window as shown in the bellow picture.
If you want to display it as a message replace the following method with your valueGen() method.
private static void valueGen(javax.swing.JTextField jTextField1) {
String x = jTextField1.getText();
System.out.println(x);
JOptionPane.showMessageDialog(null, x);
}
And use myFrame.setVisible(true); to make visible your JFrame.
public void run() {
NewJFrame myFrame = new NewJFrame();
myFrame.setVisible(true);
valueGen(myFrame.getTextField());
}
I have a function graphics() that creates my JFrame and two JRadioButtons and adds ActionListeners to them. This graphics is called from main() and graphics itself calls game().
public void game() throws Exception
{
jTextArea1.setLineWrap(true);
jTextArea1.setWrapStyleWord(true);
jTextArea1.setText("This is private information.");
jRadioButton1.setVisible(true);
jRadioButton2.setVisible(true);
try {
t.sleep(40000);
repaint();
} catch (InterruptedException e) {
// We've been interrupted: no more messages.
return;
}
After displaying "This is private information." in the text Area, I want the program execution to pause for 40 seconds, or until the user presses the JRadioButton, whichever is earlier. So I added an ActionListener and called t.interrupt() inside it.
private void jRadioButton1ActionPerformed(java.awt.event.ActionEvent evt) {
t.interrupt();
jRadioButton1.setVisible(false);
jRadioButton2.setVisible(false);
//System.out.println(t.interrupted());
jTextArea1.setText("Please wait...");
}
However, even after choosing the JRadioButton which should trigger the interrupt, that does not happen and t.interrupted returns false.
Any help would be appreciated.
Never, ever call Thread.sleep(...) on the Swing event thread as you will freeze the thread and effectively freeze your program. The solution is to consider use of a Swing Timer for the time-dependent portion of your requirement and using a SelectionListener for the JCheckBox or JRadioButton requirement.
For example:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.*;
public class PausingExecution extends JPanel {
private static final String SELECTED_TEXT = "Snafus are Better!!!";
private static final String UNSELECTED_TEXT = "Fubars Rule!!";
private static final String TIMES_UP = "Time's Up!!!!";
private static final int TIMER_DELAY = 10 * 1000;
private JTextField messageField = new JTextField(UNSELECTED_TEXT, 10);
private JCheckBox checkBox = new JCheckBox("Click Me");
public PausingExecution() {
add(messageField);
add(checkBox);
checkBox.addItemListener(new ItemListener() {
#Override
public void itemStateChanged(ItemEvent iEvt) {
if (iEvt.getStateChange() == ItemEvent.SELECTED) {
messageField.setText(SELECTED_TEXT);
} else {
messageField.setText(UNSELECTED_TEXT);
}
}
});
Timer mySwingTimer = new Timer(TIMER_DELAY, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
messageField.setText(TIMES_UP);
checkBox.setEnabled(false);
}
});
mySwingTimer.setRepeats(false);
mySwingTimer.start();
}
private static void createAndShowGui() {
PausingExecution mainPanel = new PausingExecution();
JFrame frame = new JFrame("PausingExecution");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
I have two classes in same package. i have declared a static variable in one class and want to access that variable in another class.
Here is my code in which i have declared the static variable
public class wampusGUI extends javax.swing.JFrame {
static String userCommand;
public wampusGUI() {
initComponents();
}
public void setTextArea(String text) {
displayTextArea.append(text);
}
private void enterButtonActionPerformed(java.awt.event.ActionEvent evt) {
userCommand = commandText.getText();
}
public static void main(String args[]) {
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
wampusGUI w = new wampusGUI();
w.setVisible(true);
Game g = new Game(w);
g.play();
}
});
}
}
Here is the code in which i want to access variable
public class Game {
private wampusGUI gui;
public Game(wampusGUI w) {
world = new World();
world.start();
gui = w;
}
public void play() {
gui.setTextArea(welcome());
gui.setTextArea(describe());
for (;;) {
String s = userCommand; // here value should come should
System.out.println(userCommand);
Command c = Command.create(s);
String r = c.perform(world);
// is game over?
if (r == null) {
break;
}
System.out.println(r);
}
System.out.println("Game over");
}
}
However, i can pass the variable from first class as a argument. but the problem is that, when i will run program the value is going null first time, which i dont want. i want when i enter value in textfield then it should go to another class.
Thank you.
Looking at your code, it seems you want to show dialogs to your user with a certain text
gui.setTextArea(welcome());
gui.setTextArea(describe());
and sometimes, that dialog should capture user input which is handled afterwards.
Those setTextArea calls are not what you want to use. The user will never see the welcome message as it will immediately be replaced by the describe message.
Make sure you do not block the Event Dispatch Thread (EDT) or nothing will be shown at all. I do not know what your Command class will do, but I see an infinite loop on the Event Dispatch Thread which is never a good thing. Take a look at the Concurrency in Swing tutorial for more information
Thanks to that for loop, the user will simply not be capable to input any command as the EDT is busy handling your loop. What you need is a blocking call allowing the user to provide input (not blocking the EDT, but just blocking the execution of your code). The static methods in the JOptionPane class are perfectly suited for this (e.g. the JOptionPane#showInputDialog). These methods also have a mechanism to pass the user input back to the calling code without any static variables, which solves your problem.
I suggest that you use a listener of one sort or another to allow the Game object to listen for and respond to changes in the state of the GUI object. There are several ways to do this, but one of the most elegant and useful I've found is to use Swing's own innate PropertyChangeSupport to allow you to use PropertyChangeListeners. All Swing components will allow you to add a PropertyChangeListener to it. And so I suggest that you do this, that you have Game add one to your WampusGUI class (which should be capitalized) object like so:
public Game(WampusGUI w) {
gui = w;
gui.addPropertyChangeListener(new PropertyChangeListener() {
// ....
}
This will allow Game to listen for changes in the gui's state.
You'll then want to make the gui's userCommand String a "bound property" which means giving it a setter method that will fire the property change support notifying all listeners of change. I would do this like so:
public class WampusGUI extends JFrame {
public static final String USER_COMMAND = "user command";
// ....
private void setUserCommand(String userCommand) {
String oldValue = this.userCommand;
String newValue = userCommand;
this.userCommand = userCommand;
firePropertyChange(USER_COMMAND, oldValue, newValue);
}
Then you would only change this String's value via this setter method:
private void enterButtonActionPerformed(java.awt.event.ActionEvent evt) {
setUserCommand(commandText.getText());
}
The Game's property change listener would then respond like so:
gui.addPropertyChangeListener(new PropertyChangeListener() {
#Override
public void propertyChange(PropertyChangeEvent pcEvt) {
// is the property being changed the one we're interested in?
if (WampusGUI.USER_COMMAND.equals(pcEvt.getPropertyName())) {
// get user command:
String userCommand = pcEvt.getNewValue().toString();
// then we can do with it what we want
play(userCommand);
}
}
});
One of the beauties of this technique is that the observed class, the GUI, doesn't have to have any knowledge about the observer class (the Game). A small runnable example of this is like so:
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.*;
public class WampusGUI extends JFrame {
public static final String USER_COMMAND = "user command";
private String userCommand;
private JTextArea displayTextArea = new JTextArea(10, 30);
private JTextField commandText = new JTextField(10);
public WampusGUI() {
initComponents();
}
private void setUserCommand(String userCommand) {
String oldValue = this.userCommand;
String newValue = userCommand;
this.userCommand = userCommand;
firePropertyChange(USER_COMMAND, oldValue, newValue);
}
private void initComponents() {
displayTextArea.setEditable(false);
displayTextArea.setFocusable(false);
JButton enterButton = new JButton("Enter Command");
enterButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent evt) {
enterButtonActionPerformed(evt);
}
});
JPanel commandPanel = new JPanel();
commandPanel.add(commandText);
commandPanel.add(Box.createHorizontalStrut(15));
commandPanel.add(enterButton);
JPanel mainPanel = new JPanel();
mainPanel.setLayout(new BorderLayout());
mainPanel.add(new JScrollPane(displayTextArea));
mainPanel.add(commandPanel, BorderLayout.SOUTH);
add(mainPanel);
}
public void setTextArea(String text) {
displayTextArea.append(text);
}
private void enterButtonActionPerformed(java.awt.event.ActionEvent evt) {
setUserCommand(commandText.getText());
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
WampusGUI w = new WampusGUI();
w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
w.pack();
w.setLocationRelativeTo(null);
w.setVisible(true);
Game g = new Game(w);
g.play();
}
});
}
}
class Game {
private WampusGUI gui;
public Game(WampusGUI w) {
gui = w;
gui.addPropertyChangeListener(new PropertyChangeListener() {
#Override
public void propertyChange(PropertyChangeEvent pcEvt) {
// is the property being changed the one we're interested in?
if (WampusGUI.USER_COMMAND.equals(pcEvt.getPropertyName())) {
// get user command:
String userCommand = pcEvt.getNewValue().toString();
// then we can do with it what we want
play(userCommand);
}
}
});
}
public void play() {
gui.setTextArea("Welcome!\n");
gui.setTextArea("Please enjoy the game!\n");
}
public void play(String userCommand) {
// here we can do what we want with the String. For instance we can display it in the gui:
gui.setTextArea("User entered: " + userCommand + "\n");
}
}
I agree with Jon Skeet that this is not a good solution...
But in case u want an dirty solution to ur problem then u can try this:
public class wampusGUI extends javax.swing.JFrame
{
private static wampusGUI myInstance;
public wampusGUI( )
{
myInstance = this;
initComponents();
}
public static void getUserCommand()
{
if(myInstance!=null)
{
return myInstance.commandText.getText();
}
else
{
return null;
}
}
......
......
}
in the other class use:
public void play()
{
.....
//String s = userCommand; // here value should come should
String s = wampusGUI.getUserCommand();
.....
}
This kind of code is there in some of our legacy projects... and I hate this.
I am working on an assignment, and I need to enter an SQL Query in a textfield. The user can either press the custom 'execute query' button, or they can press the enter key. When either of these are used, it is to trigger an ActionListener (no other listener is allowed). Is it as simple as writing:
if (e.getSource()=='querybutton' || e.getSource=='enter')
Or is there more to it than this?
As I said, it is a simple question (I know).
edit:
I would write this bit in my ActionPerformed as:
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==gui.executeQueryButton || e.getSource()==gui.enter)
{
String query = gui.queryText.getText();
//more code to follow
}
}
e.getSource() actually returns the object responsible for firing the event (not the name of the variable you used when creating the control). In this case, your button. You could in principle compare e.getSource() with the actual button instances. However, are you actually adding this action listener to buttons other than those two? Presumably you'd only have to add this listener to the two buttons for which you want this behavior -- in which case you wouldn't have to have this if check.
" Is it as simple as writing:
if (e.getSource()=='querybutton' || e.getSource=='enter')"
It's not simple to write this, but rather it is wrong to write it.
For one you don't want to compare Strings with ==, for another, you don't declare Strings with single quotes, and for a third, the enter key is not obtained in this way, but rather by adding the appropriate ActionListener object to the JTextField itself, and finally there should be in a single ActionListener class that handles this action, so the if block is completely unnecessary. This can probably be best done with a small inner private ActionListener class. You'd then create one object of this class and add it as an ActionListener for the querybutton and for the JTextField.
edit 1:
A more complete example of what I mean is shown below, a demo class that has a private inner handler class:
import java.awt.event.*;
import javax.swing.*;
public class ActionListenerEg extends JPanel {
private JButton queryButton = new JButton("Query");
private JTextField textField = new JTextField("hello", 20);
public ActionListenerEg() {
QueryListener qListener = new QueryListener();
queryButton.addActionListener(qListener);
textField.addActionListener(qListener);
add(queryButton);
add(textField);
}
private class QueryListener implements ActionListener {
public void actionPerformed(ActionEvent arg0) {
String textInField = textField.getText();
System.out.println("Use text in field, \"" + textInField + "\" to call SQL query in a background SwingWorker thread.");
}
}
private static void createAndShowUI() {
JFrame frame = new JFrame("ActionListenerEg");
frame.getContentPane().add(new ActionListenerEg());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}
The ActionListener is fired either by pressing the button or by pressing enter from within the JTextField. I'd then have in my control class, code that is called inside of the actinoPerformed method.
edit 2: Having most handler or "control" code in its own Handler or Control class can be a good idea, but it doesn't have to implement ActionListener interface itself, but rather just have the code that will be called from within the ActionListener codes. For example, here I try to put all the handler code in its own class. It will have different methods that are called for various situations. e.g.,
import java.awt.Component;
import java.awt.event.*;
import javax.swing.*;
public class ActionListenerEg extends JPanel {
private ActionListenerHandler handler;
private JButton queryButton = new JButton("Query");
private JButton displayButton = new JButton("Display");
private JTextField textField = new JTextField("hello", 20);
// pass in handler or handler
public ActionListenerEg(final ActionListenerHandler handler) {
this.handler = handler;
QueryListener qListener = new QueryListener();
queryButton.addActionListener(qListener);
textField.addActionListener(qListener);
displayButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (handler != null) {
handler.displayActionPerformed(e);
}
}
});
add(queryButton);
add(textField);
add(displayButton);
}
private class QueryListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (handler != null) {
String textInField = textField.getText();
handler.doQueryAction(e, textInField);
}
}
}
private static void createAndShowUI() {
ActionListenerHandler handler = new ActionListenerHandler();
JFrame frame = new JFrame("ActionListenerEg");
frame.getContentPane().add(new ActionListenerEg(handler));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}
class ActionListenerHandler {
public void displayActionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog((Component) e.getSource(), "Display things!");
}
public void doQueryAction(ActionEvent e, String textInField) {
String text = "We will use \"" + textInField + "\" to help create and run the SQL Query";
JOptionPane.showMessageDialog((Component) e.getSource(), text);
}
}
Please ask questions if it's clear as mudd, or if anything is wrong.