Re: Can you get this SwingWorker code to work more than once

Knute Johnson <>
Thu, 09 Aug 2012 09:18:22 -0700
On 8/9/2012 8:24 AM, wrote:

Here is a project that works perfectly only the first time. This is what it does on the first button press:

It starts-up with only a "Start" button.

(1) Pressing start displays "Hello World".
(2) The three "for" loops are executed in the code.
(3) "Hello World" disappears.

But, when you press the "Start" button a second time this happens:

(1) Displays "Hello World",

How do you modify the below code so that the second button press matches the first button press.

The code has a button and a label.

After answering the above question, another question that I have is: can you make this code better in any way imaginable.

Thank you,

package Test_SwingWorker;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.List;
import javax.swing.SwingWorker;

public class Test_SwingWorker extends javax.swing.JFrame
     public Test_SwingWorker()

         //The "Hello World" label that is not seen on Start-up
         jLabel1.setVisible (false);

         final Non_GUI_Stuff task = new Non_GUI_Stuff();

         jButton1.addActionListener(new ActionListener()
             public void actionPerformed(ActionEvent e)
                 //The "Hello World" label that appears when button is pressed
                 jLabel1.setVisible (true);


     private void initComponents() {

         jPanel1 = new javax.swing.JPanel();
         jButton1 = new javax.swing.JButton();
         jLabel1 = new javax.swing.JLabel();



         jLabel1.setText("Hello World");

         javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
                 .addGap(167, 167, 167)
                 .addGap(51, 51, 51)
                 .addContainerGap(55, Short.MAX_VALUE))
                 .addContainerGap(283, Short.MAX_VALUE))

         javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
             .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
             .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)


     public static void main(String args[])
         java.awt.EventQueue.invokeLater(new Runnable()
             public void run()
                 new Test_SwingWorker().setVisible(true);

class Non_GUI_Stuff extends SwingWorker<Integer, Integer>
   protected Integer doInBackground() throws Exception
       //"for" loops mentioned above
       for (int i = 0;i < 100000; i++)
           for (int i2 = 0;i2 < 100000; i2++);
       for (int i3 = 0;i3 < 100000; i3++);

     return 0;

   protected void done()
       //The "Hello World" label that disappears
       jLabel1.setVisible (false);

     private javax.swing.JButton jButton1;
     private javax.swing.JLabel jLabel1;
     private javax.swing.JPanel jPanel1;

Read the docs dude "SwingWorker is only designed to be executed once.
Executing a SwingWorker more than once will not result in invoking the
doInBackground method twice."

Just create a new SwingWorker Object and execute it again.

Your code is hard to follow and overly verbose. You could simplify it
by importing more classes. I would put the variable declarations at the
top somewhere, not because they don't work there but because it is where
one would expect to find it.

Below find some sample code for a very simple task, drawing in response
to a button press.

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

public class test extends JPanel implements ActionListener {
     private String state = "";

     public test() {
         setPreferredSize(new Dimension(400,300));

     public void actionPerformed(ActionEvent ae) {
         state = ae.getActionCommand();

     public void paintComponent(Graphics g) {
         if (state.equals("Line"))
         else if (state.equals("Oval"))
         else if (state.equals("Rect"))

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 test t = new test();
                 JFrame f = new JFrame("test");
                 JPanel p = new JPanel();
                 JButton b = new JButton("Line");
                 b = new JButton("Oval");
                 b = new JButton("Rect");

And a simplified example similar to what you were trying to do.

import java.awt.*;
import java.awt.event.*;
import java.util.concurrent.*;
import javax.swing.*;

public class test2 extends JPanel {
     private final JLabel label;

     private int count = 0;

     public test2() {
         super(new GridBagLayout());

         setPreferredSize(new Dimension(320,240));

         GridBagConstraints c = new GridBagConstraints();
         c.insets = new Insets(2,2,2,2);

         c.gridy = 0;
         c.anchor = GridBagConstraints.NORTH;
         JButton b = new JButton("Hello");
         b.addActionListener(new ActionListener() {
             public void actionPerformed(ActionEvent ae) {
                 (new DelayWorker()).execute();

         c.anchor = GridBagConstraints.CENTER;
         c.weightx = c.weighty = 1.0;
         label = new JLabel("");

     class DelayWorker extends SwingWorker<Integer,Object> {
         public Integer doInBackground() throws InterruptedException {
             return count;

         public void done() {
             try {
             } catch (InterruptedException ie) {
             } catch (ExecutionException ee) {

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame f = new JFrame("test2");
                 test2 t2 = new test2();


Knute Johnson

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