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Java - Why does my print statement not run

So this is my code:
System.out.println("System Exiting...");
long current = System.currentTimeMillis();
long disired = current + 4000;
boolean done = false;
while (!done)
{
current = System.currentTimeMillis();
if (current == disired)
{
done = true;
System.exit(0);
}
}
My problem is that the print statement doesn't run, well it does run, but it runs at the same time as the exit statement, so you don't see it
[EDIT] Ok, so i just ran this code in its own file(with nothing else), and it works as i want, it prints "system Exiting..." it waits 4 seconds, and the code exits.
so it has to be something to do with the fact that i have this code inside an event listener

Your if condition is much too restrictive since your code will almost never get the times to be exactly equal, but the change needed is very simple:
Change
// hitting this exactly is like finding the proverbial needle
// in the haystack -- almost impossible to do.
if (current == disired)
to
// this is guaranteed to work.
// note if this is in English, you'll want to change disired to desired
if (current >= disired)
Having said this, your while (true) loop is not a good thing to do as it will needlessly tie up the CPU with empty cycles. Instead use some type of event notification or call-back system like ChangeListener or a PropertyChangeListener or a Timer.
You state:
yes it is within a swing GUI
You're calling a long while (true) block of code on the Swing event thread, rendering this thread ineffective. Since the event thread is responsible for all Swing graphics and user interactions, this effectively freezes your GUI until the while loop completes. The solution is obvious: 1) use a Swing Timer for your delay, not a while true loop (this is the callback mechanism that I mentioned in my original answer), and 2) in the future, please give us this important relevant information with the original question since it changes the entire nature of the question.
e.g.
// caveat: code not tested
System.out.println("System Exiting...");
int delay = 4 * 1000;
new Timer(delay, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
System.out. println("Exited");
System.exit(0);
}
}).start();
e.g.,
import java.awt.Component;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.*;
#SuppressWarnings("serial")
public class TestDelayedExit extends JPanel {
private static final int GAP = 100;
public TestDelayedExit() {
add(new JButton(new DisposeAction("Exit", KeyEvent.VK_X)));
setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
}
private static void createAndShowGui() {
JFrame frame = new JFrame("TestDelayedExit");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new TestDelayedExit());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
private class DisposeAction extends AbstractAction {
private int count = 4;
private Timer timer;
public DisposeAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic); // for alt-key combo
}
#Override
public void actionPerformed(ActionEvent e) {
if (timer != null && timer.isRunning()) {
return;
}
final Component c = (Component) e.getSource();
int timerDelay = 1000;
putValue(NAME, String.valueOf(count));
timer = new Timer(timerDelay, new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (count == 0) {
((Timer) e.getSource()).stop();
// this will not work for JMenuItems, and for that
// you would need to get the pop up window's parent component
Window win = SwingUtilities.getWindowAncestor(c);
if (win != null) {
win.dispose();
}
} else {
count--;
putValue(NAME, String.valueOf(count));
}
}
});
timer.start();
}
}
}

How to disable a JButton for certain period of time?

I would like to disable a JButton for about 10 seconds. Is there way to do this?
Thank you

Use a Swing Timer, when triggered, it notifies the registered listener within the context of the Event Dispatching Thread, making it safe to update the UI from.
See How to use Swing Timers and Concurrency in Swing for more details

First read the answer from #MadProgrammer and go through the links provided there. If you still need a working example based on those suggestions, following is one.
why the solution is better than few solutions presented
It's because it uses a javax.swing.Timer to enable the button that enables GUI related tasks to be automatically executed on the event-dispatch thread (EDT). This saves the swing application from being intermixed with non EDT operations.
Please try the following example:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class SwingDemo extends JPanel {
private final JButton button;
private final Timer stopwatch;
private final int SEC = 10;
public SwingDemo() {
button = new JButton("Click me to disable for " + SEC + " secs");
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
JButton toDisable = (JButton) e.getSource();
toDisable.setEnabled(false);
stopwatch.start();
}
});
add(button);
stopwatch = new Timer(SEC * 1000, new MyTimerListener(button));
stopwatch.setRepeats(false);
}
static class MyTimerListener implements ActionListener {
JComponent target;
public MyTimerListener(JComponent target) {
this.target = target;
}
#Override
public void actionPerformed(ActionEvent e) {
target.setEnabled(true);
}
}
public static void main(String[] args) {
final JFrame myApp = new JFrame();
myApp.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myApp.setContentPane(new SwingDemo());
myApp.pack();
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
myApp.setVisible(true);
}
});
}
}

You can use Thread, Task or the simpler Timer class.

you can use Thread.sleep(time in mil seconds)
ex:
Thread.sleep(10000); // sleep for 10 seconds
JButton button = new JButton("Test");
try {
button.setEnabled(false);
Thread.sleep(10000);
button.setEnabled(true);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
but it must be in a separate thread or it will make all the GUI hang for 10 seconds.
you can post more details about the code and i can help

Counting and printing time in java using swing

I'm trying to implement a timer using one thread and print it on a JButton using another thread.
my class for time is like this:
public class Time extends Thread
{
int counter = 0;
public String currentTime = new String();
public String printFormat(int second)
{
return String.format("%d:%d", second/60, second%60);
}
synchronized public void count(int minute) throws InterruptedException
{
minute *= 60;
while(minute >= 0)
{
wait(1000);
minute--;
currentTime = printFormat(minute);
System.out.println(currentTime);
}
}
and my main thread is like this:
button.setText(time.currentTime);
what is wrong with this piece of code?

"if you can explain it using java swing timer , I would appreciate that"
If you want to use a javax.swing.Timer do the following, it really simple.
The same way you set a ActionListener to a button, you do the same for the timer. Except instead of the button firing the event, it's fired by the timer, every duration period you set for it.
In the case of a clock like timer, you would set it to 1000,
indication do something every 1000 milliseconds.
In this particular
example, I just set the text of the button with a count value that I
increment by one every time the timer event is fired. Heres the Timer code
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
button.setText(String.valueOf(count));
count++;
}
});
timer.start();
As you can see it' pretty simple
You can run this example
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class ButtonTimer {
private JButton button = new JButton(" ");
private int count = 1;
public ButtonTimer() {
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
button.setText(String.valueOf(count));
count++;
}
});
timer.start();
JFrame frame = new JFrame();
frame.add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new ButtonTimer();
}
});
}
}
If you want help trying to figure out your current code, consider posting a runnable program we can test out. So we can see where you're going wrong.
Here's a tutorial on Concurrency With Swing

converting to ScheduledThreadPoolExecutor

I am still a beginner at Java so I have not learned much about threads and concurrency. However, I would like to be able to use the ScheduledThreadPoolExecutor as a timer because of the problems I am having with java.util.Timer and TimerTask. I am extremely interested in the creation of threads and know that I will be learning about them in a few weeks. However, if possible could someone give me a basic example on how to convert my current mini test program using util.timer to using a ScheduledThreadPoolExecutor?
I would like to complete this example ASAP so I don't have much time to learn about threads - no matter how much I would like to. Having said this please include anything you feel is important that a java beginner should know with regards to ScheduledThreadPoolExecutor.
Example program
I have made a quick small example to represent the problem I am having in a larger program. What this program should do is allow the user to press a button to start a counter. The user must then be able to stop and restart the counter when ever s/he wants. In the larger program it is vital that this counter remains equal so I have used the
scheduleAtFixRate()
method. It is also important that the initial delay is always the same (in this case 0).
The problem (as I am sure you will see) is that once the timer is cancelled it cannot be restarted - something that I hope the ScheduledThreadPoolExecutor will resolve.
code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.TimerTask;
import java.util.Timer;
public class Tester extends JFrame {
JButton push = new JButton("Push");
static JTextArea textOut = new JTextArea();
Timer timer = new Timer();
boolean pushed = false;
static int i = 1;
public Tester() {
super();
add(push, BorderLayout.NORTH);
add(textOut);
push.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!pushed) {
timer.scheduleAtFixedRate(new Task(), 0, 1000);
pushed = true;
} else {
timer.cancel();
pushed = false;
}
}
});
}
static class Task extends TimerTask {
public void run() {
textOut.setText("" + i++);
}
}
public static void main(String[] args) {
Tester a = new Tester();
a.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
a.pack();
a.setVisible(true);
}
}
I use this class a lot for testing so there may be extra code (I think I removed it all).

Replace
Timer timer = new Timer();
with
ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
and
class Task extends TimerTask
with
class Task implements Runnable
and
timer.scheduleAtFixedRate(new Task(), 0, 1000);
with
service.scheduleAtFixedRate(new Task(), 0, 1000, TimeUnit.MILLISECONDS);
BTW You should not be attempting to update the GUI on another thread. Instead you have to add a task to the Swing GUI Thread to perform the task
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
textOut.setText("" + i++);
}
});

how to close a java frame with threads

I have a java frame that I want to close it automatically after 3 or 4 seconds. I found out I must used threads. but I dont know how exactly to do it, this a dumy part of my code :
package intro;
import java.awt.*;
import java.io.IOException;
//import view.LangMenu;
public class IntroClass extends Frame {
private int _screenWidth = 0;
private int _screenHeight = 0;
private int _screenCenterx = 0;
private int _screenCentery = 0;
//private static final String SOUND_PATH="/sounds/introSound.midi";
public IntroClass() {
Toolkit thisScreen = Toolkit.getDefaultToolkit();
Dimension thisScrrensize = thisScreen.getScreenSize();
_screenWidth = thisScrrensize.width;
_screenHeight = thisScrrensize.height;
_screenCenterx = _screenWidth / 2;
_screenCentery = _screenHeight / 2;
setBackground(Color.pink);
Label lbl = new Label("Welcome To Dots Game. Samaneh Khaleghi", Label.CENTER);
add(lbl);
setUndecorated(true);
setLocation((_screenCenterx*50)/100,_screenCentery-(_screenCentery*50)/100);
setSize((_screenWidth * 50) / 100, (_screenHeight * 50) / 100);
WaitClass r = new WaitClass();
r.start();
view.DotsBoardFrame d=new view.DotsBoardFrame();
main.Main.showScreen(d);
}
class WaitClass extends Thread {
boolean running = true;
public void run() {
while (running) {
try {
Thread.sleep(50);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
}
}
}
}

Although AWT is supposed to be thread-safe, it isn't really. So I suggest, like Swing, do all the GUI manipulation on the AWT Event Dispatch Thread (EDT).
For this particular task, javax.swing.Timer should do the trick. (Although it is in the javax.swing package, there is nothing Swing-specific about it.)
Also I would strongly suggest not extending classes unless you really have to. There is very little reason ever to extend Thread or Frame (unfortunately there are lots of bad examples and old tutorials out there).

in your frame start a new thread and pass to it your frame instance, and after a specific period of time close it.
class MyThread extends Thread {
private JFrame frame;
//-- getters and setters for frame
public void run() {
Thread.sleep(1000); //close the frame after 1 second.
frame.close();
}
}
and in your JFrame class, in the constructor specifically put the following line of code:
MyThread th = new MyThread();
th.setFrame(this);
th.start();

You can use a Timer and let it take care of threads for you.