Unable to update JDialog GUI inside a thread

Question

Please have a look at the following code

private class EmergencyAlertNotifier implements Runnable, ActionListener
    {
        JDialog dialog = new JDialog();
        int number=0;

        JLabel message;
        JButton yes,no;

        String messageStr;

        public EmergencyAlertNotifier()
        {
            dialog.setLayout(new BorderLayout());

            //The JLabel which will display the number of seconds left
            //before alerting emergency services
            message = new JLabel();


             messageStr="number";

            yes = new JButton("OK");
            yes.addActionListener(this);
            no = new JButton("Cancel");
            no.addActionListener(this);

            JPanel btnPanel = new JPanel();
            btnPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
            btnPanel.add(yes);
            btnPanel.add(no);

            dialog.add(message,"Center");
            dialog.add(btnPanel,"South");

            dialog.setTitle("Ready To Notify Emergency Fire Services");
            dialog.setVisible(true);
            dialog.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        }

        @Override
        public void run() 
        {
            for(int i=10;i>0;i--)
            {
                message.setText(messageStr+i+" Sec.");


                try
                {
                    Thread.sleep(1000);
                }
                catch(Exception e)
                {
                    e.printStackTrace();
                }
            }


        }

        @Override
        public void actionPerformed(ActionEvent e) 
        {
            if(e.getSource()==yes)
            {

            }
            else
            {
                dialog.dispose();
            }
        }

    }

Thread is started outside the above class

 new Thread(new EmergencyAlertNotifier()).start();

I am trying to update the JLabel with the changing numbers inside the thread. But instead, the JLabel is not coming to the GUI. Why is that? Please help!

First of all, never, ever create, modify or interact with any UI component from any thread other the the Event Dispatching Thread, check out [Concurrency in Swing](http://docs.oracle.com/javase/tutorial/uiswing/concurrency/index.html) for more details. Secondly, I don't see any where where you start a thread so you already be executing within the context of EDT, which means you are blocking it, preventing from updating the UI — MadProgrammer, Mar 23 '13 at 06:08
@MadProgrammer: Thanks for the reply. Please have a look at the edit — PeakGen, Mar 23 '13 at 06:14
OK, I managed to solve the issue. Thanks everyone for the replies :) — PeakGen, Mar 23 '13 at 06:18
I would suggest you use something like a SwingWorker. Can I ask how you got it working? — MadProgrammer, Mar 23 '13 at 07:14
@MadProgrammer: Yes sure, you are a very good helper so why not? :) Actually, inside my original JLabel, I have used html tags. Same text contained a part which do not have html. I removed the html! Thats all! :D — PeakGen, Mar 23 '13 at 08:17
That's what I was afraid of. Your thread is violating the sing thread rules of Swing. You should only ever create/modify/interact with the UI components from the Event Dispatching Thread — MadProgrammer, Mar 23 '13 at 08:22
@MadProgrammer: I think you are correct. My thread it not closing even the GUI is gone! ahhhhhhhhhhh! I am moving with Timer — PeakGen, Mar 23 '13 at 13:07

score 4 · Accepted Answer · answered Mar 23 '13 at 08:13

there are a few issue in your code, with Concurency in Swing,
please I can't comment that somehow,
untill SwingWorker will implemented in official API, Runnable#Thread was standard workaround for Workers Thread,
for production code to use Runnable#Thread instead of SwingWorker (my view, disagree with black hole implemented in API)
output from Runnable#Thread to the Swing GUI required usage of invokeLater, for thread_safe (setText, append... , especially there were chnages in Java7 in compare with Java6) methods too
use util.Timer for count_down, instead of Thread.sleep()

modified code, works as expected

import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class EmergencyAlertNotifier implements Runnable, ActionListener {

    private JDialog dialog = new JDialog();
    private int number = 0;
    private JLabel message;
    private JButton yes, no;
    private String messageStr;
    private boolean runProcess = true;

    public EmergencyAlertNotifier() {
        dialog.setLayout(new GridLayout());
        //The JLabel which will display the number of seconds left
        //before alerting emergency services
        message = new JLabel();
        messageStr = "number";
        yes = new JButton("OK");
        yes.addActionListener(this);
        no = new JButton("Cancel");
        no.addActionListener(this);
        JPanel btnPanel = new JPanel();
        btnPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
        btnPanel.add(yes);
        btnPanel.add(no);
        dialog.add(message, "Center");
        dialog.add(btnPanel, "South");
        dialog.setTitle("Ready To Notify Emergency Fire Services");
        dialog.pack();
        dialog.setVisible(true);
        dialog.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        new Thread(this).start();
    }

    @Override
    public void run() {
        while (runProcess) {
            for (int i = 10; i > 0; i--) {
                message.setText(messageStr + " " + i + " Sec.");
                try {
                    Thread.sleep(1000);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
            runProcess = false;
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == yes) {
        } else {
            dialog.dispose();
        }
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                EmergencyAlertNotifier ean = new EmergencyAlertNotifier();
            }
        });
    }
}

An alternative using `javax.swing.Timer` is shown [here](http://stackoverflow.com/a/12451673/230513). — trashgod, Mar 23 '13 at 10:29
Thanks for the reply :). I think you are correct. My thread it not closing even the GUI is gone! ahhhhhhhhhhh! I am moving with Timer — PeakGen, Mar 23 '13 at 13:07

Unable to update JDialog GUI inside a thread

1 Answers1