How to Continuously Update JLabel with Results of Long-Running Task?

Update JLabel with Results of Long-Running Task

Problem:

You aim to create a program that continuously pings a server and updates the ping results in a JLabel.

Initial Approach:

Your first attempt involved calling the setPing() method once within the formWindowOpened() event. While this worked, it only performed the task once.

Second Approach:

Subsequent efforts introduced an infinite loop within formWindowOpened(). However, this approach failed to execute the setPing() method even once.

Solution using Swing Timer and SwingWorker:

To address this issue, consider utilizing a Swing Timer to schedule the execution of a long-running task (in this case, the setPing() method) at predefined intervals. This approach leverages a SwingWorker to execute the setPing() method on a separate thread, enabling responsiveness and avoiding GUI freezing.

Here's a code snippet that implements this approach:

<code class="java">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);
    }
}</code>

In this code:

• Swing Timer repeatedly schedules the execution of the PingWorker.
• SwingWorker executes setPing() in the background, updating the GUI on completion.

This approach ensures that the long-running task does not block the GUI thread, maintaining responsiveness while updating the JLabel with ping results at regular intervals.

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