How to Manage Multiple SwingWorker Threads and Their Associated Labels in a JApplet?-javaTutorial-php.cn

How to Manage Multiple SwingWorker Threads and Their Associated Labels in a JApplet?

Mary-Kate Olsen

Release： 2024-12-20 02:33:08

Original

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How to Manage Multiple SwingWorker Threads and Their Associated Labels in a JApplet?

Waiting for Multiple SwingWorkers

Problem

Consider the following code fragment:

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.lang.reflect.InvocationTargetException;
import javax.swing.*;

public class TestApplet extends JApplet
{
    @Override
    public void init()
    {
        try
        {
            SwingUtilities.invokeAndWait(new Runnable()
            {
                @Override
                public void run()
                {
                    createGUI();
                }
            });
        }
        catch(InterruptedException | InvocationTargetException ex)
        {
        }
    }

    private void createGUI()
    {
        getContentPane().setLayout(new FlowLayout());
        JButton startButton = new JButton("Do work");
        startButton.addActionListener(new ActionListener()
        {
            @Override
            public void actionPerformed(ActionEvent ae)
            {
                JLabel label = new JLabel();
                new Worker(label).execute();
            }
        });
        getContentPane().add(startButton);
    }

    private class Worker extends SwingWorker<Void, Void>
    {
        JLabel label;

        public Worker(JLabel label)
        {
            this.label = label;
        }

        @Override
        protected Void doInBackground() throws Exception
        {
            // do work
            return null;
        }

        @Override
        protected void done()
        {
            getContentPane().remove(label);
            getContentPane().revalidate();
        }
    }
}

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Here the goal is to add a label to the applet that displays some intermediate results of the Worker thread (using publish/process methods). At the end, the label is removed from the applet's pane. The question is, how could one create several labels, each with its own Worker thread, and remove them when they are all done?

Solution

A CountDownLatch works well in this context. In the example below, each worker invokes latch.countDown() on completion, and a Supervisor worker blocks on latch.await() until all tasks complete. For demonstration purposes, the Supervisor updates the labels. Wholesale removal, shown in comments, is technically possible but generally unappealing. Instead, consider a JList or JTable.

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import javax.swing.*;

/**
* @see https://stackoverflow.com/a/11372932/230513
* @see https://stackoverflow.com/a/3588523/230513
*/
public class WorkerLatchTest extends JApplet {

    private static final int N = 8;
    private static final Random rand = new Random();
    private Queue<JLabel> labels = new LinkedList<JLabel>();
    private JPanel panel = new JPanel(new GridLayout(0, 1));
    private JButton startButton = new JButton(new StartAction("Do work"));

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame();

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