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What is the importance of a SwingWorker class in Java?
A SwingWorker class enables us to perform an asynchronous task in a worker thread (such as a long-running task) then update Swing components from the Event Dispatch Thread (EDT) based on the task results. It was introduced in Java 1.6 Version.
SwingWorker class
- The java.swing.SwingWorker class is a task worker, which performs time-consuming tasks in the background.
- A SwingWorker instance interacts with 3 threads, Current thread, the Worker thread, and the Event Dispatch thread(EDT).
- The Current thread calls the execute() method to kick off the task to the background and returns immediately.
- The Worker thread executes our own version of the doInBackground() method continuously in the background.
- The Event Dispatch Thread (EDT) wakes up from time to time to notify us of what happened in the Worker thread.
- When doInBackground() is ended, the Event Dispatch Thread (EDT) notify us by call our version of the done() method.
- To publish intermediate values, we can call the publish(V) method in doInBackground(). The Event Dispatch Thread (EDT) notifies us by calling our version of the process(List) method.
- To update the progress property, we can call the setProgress(i) method in doInBackground(). The Event Dispatch Thread (EDT) notifies us by calling our version of a PropertyChangeListener class.
- The java.swing.JProgressbar class is a UI component designed to show the progress of a background task implemented as a SwingWorker instance.
Example
import java.awt.*;
import java.awt.event.*;;
import javax.swing.*;
public class SwingWorkerTest {
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
JButton button = new JButton();
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
new GUIWorker().execute();
}
});
button.setText("Click Me !!!");
frame.getContentPane().add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setSize(350, 300);
frame.setVisible(true);
}
});
}
}
class GUIWorker extends SwingWorker {
private JFrame frame = new JFrame();
private JDialog dialog = new JDialog(frame, "Swingworker Test", true);
private JProgressBar progressBar = new JProgressBar();
public GUIWorker() {
progressBar.setString("Waiting on time");
progressBar.setStringPainted(true);
progressBar.setIndeterminate(true);
dialog.getContentPane().add(progressBar);
dialog.setSize(350, 300);
dialog.setModal(false);
dialog.setLocationRelativeTo(null);
dialog.setVisible(true);
}
@Override
protected Integer doInBackground() throws Exception {
System.out.println( "GUIWorker doInBackground()" );
Thread.sleep(10000);
return 0;
}
@Override
protected void done() {
System.out.println("done");
JLabel label = new JLabel("Task Complete");
dialog.getContentPane().remove(progressBar);
dialog.getContentPane().add(label);
dialog.getContentPane().validate();
}
}Output
Updated on: 11-Feb-2020
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