Update Jlabel Repeatedly with Results of Long Running Task

Update JLabel repeatedly with results of long running task

Use a Swing Timer for repeating tasks & a SwingWorker for long running tasks. E.G. of both below - it uses a Timer to repeatedly perform a 'long running' task (a ping) in a SwingWorker.

See Concurrency in Swing for more details on the Event Dispatch Thread and doing long running or repeating tasks in a GUI.

This code combines a long running task ('pinging' a server) using SwingWorker invoked from a repeating task (updating the JLabel repeatedly with the times) using a Swing based Timer.

import java.awt.event.*;
import javax.swing.*;
import java.net.Socket;

public class LabelUpdateUsingTimer {

    static String hostnameOrIP = "stackoverflow.com";
    int delay = 5000;
    JLabel label = new JLabel("0000");

    LabelUpdateUsingTimer() {
        label.setFont(label.getFont().deriveFont(120f));

        ActionListener timerListener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                new PingWorker().execute();
            }
        };
        Timer timer = new Timer(delay, timerListener);

        timer.start();
        JOptionPane.showMessageDialog(
                null, label, hostnameOrIP, JOptionPane.INFORMATION_MESSAGE);
        timer.stop();
    }

    class PingWorker extends SwingWorker {

        int time;

        @Override
        protected Object doInBackground() throws Exception {
            time = pingTime();
            return new Integer(time);
        }

        @Override
        protected void done() {
            label.setText("" + time);
        }
    };

    public static int pingTime() {
        Socket socket = null;
        long start = System.currentTimeMillis();
        try {
            socket = new Socket(hostnameOrIP, 80);
        } catch (Exception weTried) {
        } finally {
            if (socket != null) {
                try {
                    socket.close();
                } catch (Exception weTried) {}
            }
        }
        long end = System.currentTimeMillis();
        return (int) (end - start);
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                new LabelUpdateUsingTimer();
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

How to force java to draw swing label?

Try this

int delay = 1000; //milliseconds
  ActionListener taskPerformer = new ActionListener() {
      public void actionPerformed(ActionEvent evt) {
          //...Perform a task...
      }
  };
  new Timer(delay, taskPerformer).start();

Using Swingworker to constantly update a GUI

Here is a complete example i really like Swing Worker Example

You have to use publish() and override process()

Example:

class Worker extends SwingWorker<Void, String> {

    @Override
    protected void doInBackground() throws Exception {
       //here you make heavy task this is running in another thread not in EDT
       //process after some time call publish() 

    }

    @Override
    protected void process(List<String> chunks) {
        //this is executed in the EDT
        //here you update your label
    }
}

Swing - revalidate of UI not happening

The thing is, that actions in public void actionPerformed(ActionEvent ae) method execute in Swing thread. The changes are not shown till all of actions are executed. You can, for example, perform your doStaff method in another thread.
For more details, see this topic. I had the same problem.

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