Removing Undefined JProgressBar

Please try to go through this code, its working code for JProgressBar with SwingWorker, and then, as soon as you understand its work, do not hesitate to implement it on your way.

 import java.awt.*;

 import java.awt.event.*;

 import java.util.List;

 import javax.swing.*;


 public class ProgressBarTest
 {
    public static void main(String[] args)
    {
       EventQueue.invokeLater(new Runnable()
          {
             public void run()
             {
                JFrame frame = new ProgressBarFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
             }
         });
    }
 }

 /**
 * A frame that contains a button to launch a simulated activity, a progress bar, and a
  * text area for the activity output.
  */
 class ProgressBarFrame extends JFrame
 {
    public ProgressBarFrame()
    {
       setTitle("ProgressBarTest");
       setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

       // this text area holds the activity output
       textArea = new JTextArea();

       // set up panel with button and progress bar
       final int MAX = 1000;
       JPanel panel = new JPanel();
       startButton = new JButton("Start");
       progressBar = new JProgressBar(0, MAX);
       progressBar.setStringPainted(true);
       panel.add(startButton);
       panel.add(progressBar);

       checkBox = new JCheckBox("indeterminate");
       checkBox.addActionListener(new ActionListener()
          {
             public void actionPerformed(ActionEvent event)
             {
                progressBar.setIndeterminate(checkBox.isSelected());
                progressBar.setStringPainted(!progressBar.isIndeterminate());
             }
          });
       panel.add(checkBox);
       add(new JScrollPane(textArea), BorderLayout.CENTER);
       add(panel, BorderLayout.SOUTH);

       // set up the button action

       startButton.addActionListener(new ActionListener()
         {
             public void actionPerformed(ActionEvent event)
             {
                startButton.setEnabled(false);
                activity = new SimulatedActivity(MAX);
                activity.execute();
             }
          });
    }

    private JButton startButton;
    private JProgressBar progressBar;
    private JCheckBox checkBox;
    private JTextArea textArea;
    private SimulatedActivity activity;

    public static final int DEFAULT_WIDTH = 400;
    public static final int DEFAULT_HEIGHT = 200;

    class SimulatedActivity extends SwingWorker<Void, Integer>
    {
       /**
        * Constructs the simulated activity that increments a counter from 0 to a
        * given target.
        * @param t the target value of the counter.
        */
       public SimulatedActivity(int t)
       {
          current = 0;
          target = t;
       }
       protected Void doInBackground() throws Exception
       {
         try
          {
             while (current < target)
             {
                Thread.sleep(100);
                current++;
                publish(current);
             }
          }
          catch (InterruptedException e)
          {
          }
          return null;
       }

       protected void process(List<Integer> chunks)
       {
          for (Integer chunk : chunks)
          {
             textArea.append(chunk + "\n");
             progressBar.setValue(chunk);
          }
       }

       protected void done()
       {
         startButton.setEnabled(true);
      }

      private int current;
       private int target;
    }
 }