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Swing - Thread.sleep() stop JTextField.setText() working [duplicate]

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Closed 10 years ago.
Possible Duplicate:
using sleep() for a single thread
I'm having issues with JTextField.setText() when using Thread.sleep(). This is for a basic calculator I'm making. When the input in the input field is not of the correct format I want "INPUT ERROR" to appear in the output field for 5 seconds and then for it to be cleared. The setText() method did work when I just set the text once to "INPUT ERROR" and by printing out the text in between I found it does work with both that and the setText("") one after the other. The problem arises when I put the Thread.sleep() between them.
Here's a SSCCE version of the code:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.regex.Pattern;
import javax.swing.*;
public class Calc {
static Calc calc = new Calc();
public static void main(String args[]) {
GUI gui = calc.new GUI();
}
public class GUI implements ActionListener {
private JButton equals;
private JTextField inputField, outputField;
public GUI() {
createFrame();
}
public void createFrame() {
JFrame baseFrame = new JFrame("Calculator");
baseFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel contentPane = new JPanel();
BoxLayout layout = new BoxLayout(contentPane, BoxLayout.Y_AXIS);
contentPane.setLayout(layout);
baseFrame.setContentPane(contentPane);
baseFrame.setSize(320, 100);
equals = new JButton("=");
equals.addActionListener(this);
inputField = new JTextField(16);
inputField.setHorizontalAlignment(JTextField.TRAILING);
outputField = new JTextField(16);
outputField.setHorizontalAlignment(JTextField.TRAILING);
outputField.setEditable(false);
contentPane.add(inputField);
contentPane.add(outputField);
contentPane.add(equals);
contentPane.getRootPane().setDefaultButton(equals);
baseFrame.setResizable(false);
baseFrame.setLocation(100, 100);
baseFrame.setVisible(true);
}
/**
* When an action event takes place, the source is identified and the
* appropriate action is taken.
*/
#Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == equals) {
inputField.setText(inputField.getText().replaceAll("\\s", ""));
String text = inputField.getText();
System.out.println(text);
Pattern equationPattern = Pattern.compile("[\\d(][\\d-+*/()]+[)\\d]");
boolean match = equationPattern.matcher(text).matches();
System.out.println(match);
if (match) {
// Another class calculates
} else {
try {
outputField.setText("INPUT ERROR"); // This doesn't appear
Thread.sleep(5000);
outputField.setText("");
} catch (InterruptedException e1) {
}
}
}
}
}
}
I'm not actually using a nested class but I wanted it to be able to be contained in one class for you. Sorry about how the GUI looks but again this was to cut down the code. The the important section (if (e.getSource() == equals)) remains unchanged from my code. The simplest way to give an incorrect input is to use letters.

When you use Thread.sleep() you're doing it on the main thread. This freezes the gui for five seconds then it updates the outputField. When that happens, it uses the last set text which is blank.
It's much better to use Swing Timers and here's an example that does what you're trying to accomplish:
if (match) {
// Another class calculates
} else {
outputField.setText("INPUT ERROR");
ActionListener listener = new ActionListener(){
public void actionPerformed(ActionEvent event){
outputField.setText("");
}
};
Timer timer = new Timer(5000, listener);
timer.setRepeats(false);
timer.start();
}

As Philip Whitehouse states in his answer, you are blocking the swing Event Dispatch Thread with the Thread.sleep(...) call.
Given that you've taken the time to set up an ActionListener already, it would probably be easiest to use a javax.swing.Timer to control clearing the text. To do this, you could add a field to your GUI class:
private Timer clearTimer = new Timer(5000, this);
In the constructor for GUI, turn off the repeats feature, as you really only need a one-shot:
public GUI() {
clearTimer.setRepeats(false);
createFrame();
}
Then, actionPerformed can be modified to use this to start the timer/clear the field:
public void actionPerformed(ActionEvent e) {
if (e.getSource() == equals) {
inputField.setText(inputField.getText().replaceAll("\\s", ""));
String text = inputField.getText();
System.out.println(text);
Pattern equationPattern = Pattern.compile("[\\d(][\\d-+*/()]+[)\\d]");
boolean match = equationPattern.matcher(text).matches();
System.out.println(match);
if (match) {
// Another class calculates
} else {
clearTimer.restart();
outputField.setText("INPUT ERROR"); // This doesn't appear
}
} else if (e.getSource() == clearTimer) {
outputField.setText("");
}
}

You're doing a Thread.sleep() in the Swing main thread. This is NOT good practice. You need to use a SwingWorker thread at best.
What's happening is that it's running the first line, hitting Thread.sleep().
This prevents the (main) EDT thread from doing any of the repaints (as well as preventing the next line executing).
You should use a javax.swing.Timer to setup the delayed reaction and not put sleep() calls in the main thread.

I have a issue with java threads and KeyEvents?

I need a bit of help with my program here. I have a blocking function waiting in my main thread for the user to click "Enter". Then, when the user hits enter, the keypressed event should fire, which will unblock the blocking function. However, when the program hits the blocking function, it simply freezes up and doesn't register the key pressed event.
So, my question is, is a event a runnable, which is added to a thread whenever the user clicks enter? If so, my code should have worked, right? If this is not the case, and each event is not a separate thread, could anyone enlighten me on how I should fix my problem here?
my blocking function:
public String getInput() {
synchronized(waitObject) {
try {
System.out.println("waiting");
waitObject.wait(); // throws exception, cba to add it here
} catch (Exception ex) {
ex.printStackTrace();
}
}
return(myString);
}
my keylistener code:
public void keyPressed(KeyEvent e) {
System.out.println("key pressed");
char c = e.getKeyChar();
if (c == e.VK_ENTER) {
System.out.println("Enter pressed");
synchronized(waitObject) {
waitObject.notifyAll();
}
}
}
and the function getting the input:
private String getCommand() {
System.out.println("getting command");
CommandField command = new CommandField((JFrame)(this));
command.setPreferredSize(new Dimension(getWidth(), 30));
m_panel.add(command, BorderLayout.NORTH);
validate();
command.requestFocus();
System.out.println(command.getInput());
return null;
}
And this function is called from another keylistener:
public class Listener implements KeyListener {
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_F2) {
System.out.println(getCommand());
}
}
public void keyReleased(KeyEvent e) {
}
public void keyTyped(KeyEvent e) {
}
}

OK, getCommand() is called on the event thread which then calls getInput() on the same thread, which then calls Object#wait() on the event thread, so yes you are tying up the event thread and effectively freezing your program.
None of this is needed, and a much easier fix is possible if you code using the concepts of event-driven programming. You don't want to call wait() in a Swing GUI and in your situation don't need to call it, but rather you want to change how your program responds to input based on its state. If you tell us more on the exact behavior you're trying to elicit, we can probably help you find a much better solution.
Edit
Consider using a JOptionPane or a modal JDialog for displaying a "blocking" window that stops the main program until the dialog has been dealt with.

Starting with ImageApp, I added the following key binding in the constructor. It will show() the popup menu when pressing the Enter key. You can change the arbitrary location to suit your usage.
this.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0), "showPopup");
this.getActionMap().put("showPopup", new AbstractAction("showPopup") {
#Override
public void actionPerformed(ActionEvent e) {
popup.show(ImageApp.this, 42, 42);
}
});
Addendum: To bring up a modal input dialog, so something like this:
this.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0), "dialog");
this.getActionMap().put("dialog", new AbstractAction("dialog") {
#Override
public void actionPerformed(ActionEvent e) {
String value = JOptionPane.showInputDialog("What?");
System.out.println(value);
}
});

Java Swing: Focus issue

I'm making a level editor for my game. I have a property panel where I can modify the selected object its properties. I also have a Save button to write the level xml.
A field-edit is submitted(*) when the editor component lost the focus or Enter is pressed. This is working great, but the only problem is that when I have this sequence of actions:
Edit a field
Press the save button
Because, what happens is this:
I edit the field
I press the save button
The level is saved
The field lost the focus
The edit is submitted
As you can see, this is the wrong order. Of course I want the field to lose its focus, which causes the submit and then save the level.
Is there a trick, hack or workaround to make the field first lose the focus and then perform the action listener of the save button?
Thanks in advance.
(* submit = the edit to the field is also made in the object property)
EDIT: For the field I'm using a FocusAdapter with focusLost:
FocusAdapter focusAdapter = new FocusAdapter()
{
#Override
public void focusLost(FocusEvent e)
{
compProperties.setProperty(i, getColor());
record(); // For undo-redo mechanism
}
};
And for the button a simple ActionListener with actionPerformed`.
btnSave.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
// Save the level
}
});

Hmm ... can't reproduce: in the snippet below the lost is always notified before the actionPerfomed, independent on whether I click the button or use the mnemonic:
final JTextField field = new JTextField("some text to change");
FocusAdapter focus = new FocusAdapter() {
#Override
public void focusLost(FocusEvent e) {
LOG.info("lost: " + field.getText());
}
};
field.addFocusListener(focus);
Action save = new AbstractAction("save") {
#Override
public void actionPerformed(ActionEvent e) {
LOG.info("save: " + field.getText());
}
};
save.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_S);
JButton button = new JButton(save);
JComponent box = Box.createHorizontalBox();
box.add(field);
box.add(button);
On the other hand, focus is a tricky property to rely on, the ordering might be system-dependent (mine is win vista). Check how the snippet behave on yours.
If you see the same sequence as I do, the problem is somewhere else
if you get the save before the lost, try to wrap the the save action into invokeLater (which puts it at the end of the EventQueue, so it's executed after all pending events)
Action save = new AbstractAction("save") {
#Override
public void actionPerformed(ActionEvent e) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
LOG.info("save: " + field.getText());
}
});
}
};

Normally, wrapping your save code into an SwingUtilities.invokeLater() should do the trick. As you already mentioned, this doesn't work? Try this:
private boolean editFocus = false;
FocusAdapter focusAdapter = new FocusAdapter()
{
#Override
public void focusGained(FocusEvent e){
editFocus = true;
}
#Override
public void focusLost(FocusEvent e){
compProperties.setProperty(i, getColor());
record(); // For undo-redo mechanism
editFocus = false;
if (saveRequested){
save();
}
}
};
and for your button:
private boolean saveRequested = false;
btnSave.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
if (editFocus){
saveRequested = true;
return;
} else {
save();
}
}
});
and then your save method:
private void save(){
// do your saving work
saveRequested = false;
}
This only works when your focusLost gets called after your button's action. If suddenly the order is correct, this code will get save() called twice.
But again, wrapping your save() code in your original approach should work, because the save code will execute after processing all events. That is after processing your button click and your focusLost events. Because your focusLost code executes immediately (it's not wrapped in an invokeLater()), the focusLost code should be executed always before your save code. This does not mean that the event order will be correct! But the code associated to the events will executed in the right order.

Programmatically Generating Actionevent in Java

I'm making an App. in java , in which there is a Button to which I have added an actionlistener. The ActionEvent it(the button) generates executes some code. Now I want this piece of code to run whenever the app. starts and without pressing the button. I mean, I want to generate the Actionevent (without pressing the button) so that the piece of code the ActionPerformed contains gets executed as the app. start. After that, it may run whenever I press the button.

You can create ActionEvents like any other Java Object by just using the constructor. And then you can send them directly to the component with Component.processEvent(..)
However, in this case I think you are better making your code into a separate function which is called both:
By the ActionListener when the button is pressed
Directly by your application startup code (possibility using SwingUtilities.invokeLater() or SwingUtilities.invokeAndWait() if you need it to happen on the event-handling thread)
This way you don't mix up presentation logic with the business logic of whatever the code does....

Yes it can be done, but it doesn't really make sense, since your goal isn't to press a button or to call an ActionListener's code, but rather to have a common behavior on button press and on program start up. To me the best way to achieve this is to have a method that is called by both the actionPerformed method of the ActionListener and by the class at start up.
Here's a simple example. In the code below, a method disables a button, turns the JPanel green, and starts a Timer that in 2 seconds enables the button and resets the JPanel's background color to its default. The method that causes this behavior is called both in the main class's constructor and in the JButton's ActionListener's actionPerformed method:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ActionOnStartUp extends JPanel {
private static final int PANEL_W = 400;
private static final int PANEL_H = 300;
private static final int TIMER_DELAY = 2000;
private JButton turnGreenBtn = new JButton("Turn Panel Green for 2 seconds");;
public ActionOnStartUp() {
turnPanelGreen();
turnGreenBtn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
turnPanelGreen();
}
});
add(turnGreenBtn);
}
public void turnPanelGreen() {
setBackground(Color.green);
turnGreenBtn.setEnabled(false);
new Timer(TIMER_DELAY, new ActionListener() {
public void actionPerformed(ActionEvent ae) {
setBackground(null);
turnGreenBtn.setEnabled(true);
((Timer) ae.getSource()).stop(); // stop the Timer
}
}).start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PANEL_W, PANEL_H);
}
public static void createAndShowGui() {
JFrame frame = new JFrame("Foo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ActionOnStartUp());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Usually, the button action event responds to an external event, to notify the application that the user (or rather something or someone) interacted with the application. If your button executes some code that you want to also execute at application start, why not just place everything at it's proper place?
Example:
public class SomeSharedObject {
public void executeSomeCode() { /*....*/ }
}
Set the button with something like
public void setButtonAction(final SOmeSharedObject obj) {
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
obj.executeSomeCode();
}
});
}
And run at application start with something like
public void initApplication(SomeSharedObject obj) {
obj.executeSomeCode();
}
And, if the code you need to execute takes a while to complete, you might want to use a separate thread inside your actionPerformed button event so your application UI does not freeze up.

Just Call JButton.doClick() it should fire the ActionEvent associated with the JButton.

Can't get keyboard focus on JTextField in JDialog

I have a Swing app that has a JDialog pop up and ask for a username and password. I thought it'd be good to have the keyboard focus already in the username field, but everything I've tried so far doesn't work (even though one solution I tried works for a different text field in the program), so....I need some help. Here's my code:
//JTextField usernameField = ...
JDialog dialog = pane.createDialog("Password:");
dialog.setVisible(true);
//Take 1
usernameField.requestFocusInWindow();
//Take 2
dialog.addWindowFocusListener(new WindowAdapter() {
public void windowGainedFocus(WindowEvent e) {
usernameField.requestFocusInWindow();
}
});
//Take 3 - This is what I used elsewhere quite successfully
dialog.addComponentListener(new ComponentAdapter() {
public void componentShown(ComponentEvent e ) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
usernameField.requestFocusInWindow();
}
});
}
});
For what it's worth, this is with Linux / X11 / Openbox. And when I use GTK, I have to press Tab once to select the appropriate field, but when I use Metal, I have to press it twice.
Thanks in advance.

See Dialog Focus for tips & strategies.