Java: Timer with ProgressBar

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

public class NewMain{
    final static int interval = 1000;
    int i;
    JLabel label;
    JProgressBar pb;
    Timer timer;
    JButton button;

public NewMain() {
    JFrame frame = new JFrame("Swing Progress Bar");

    button = new JButton("Start");
    button.addActionListener(new ButtonListener());

    pb = new JProgressBar(0, 20);
    pb.setValue(0);
    pb.setStringPainted(true);

    label = new JLabel("c");

    JPanel panel = new JPanel();
    panel.add(button);
    panel.add(pb);

    JPanel panel1 = new JPanel();
    panel1.setLayout(new BorderLayout());
    panel1.add(panel, BorderLayout.NORTH);
    panel1.add(label, BorderLayout.CENTER);
    panel1.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
    frame.setContentPane(panel1);
    frame.pack();
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create a timer. (Timer Stop with Action)
    timer = new Timer(interval, new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            if (i == 20){
                Toolkit.getDefaultToolkit().beep();
                timer.stop();
                button.setEnabled(true);
                pb.setValue(0);
                String str = "<html>" + "<font color=\"#FF0000\">" + "<b>" +
                "Downloading completed." + "</b>" + "</font>" + "</html>";
                label.setText(str);
            }

            i = i + 1;
            pb.setValue(i);

            }
        });
      }

  //Timer Event (Timer Start)
  class ButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent ae) {
        button.setEnabled(false);
        i = 0;
        String str = "<html>" + "<font color=\"#008000\">" + "<b>" +
        "Downloading is in process......." + "</b>" + "</font>" + "</html>";
        label.setText(str);
        timer.start();
        }
    }


  public static void main(String[] args) {
    NewMain spb = new NewMain();
    }
}