Program to demonstrate working of JProgressBar in Java using Swing API
package com.hubberspot.swing.code;
import javax.swing.*;
public class ProgressBarDemo extends JPanel {
// 1. Create a instance variable of JProgressBar
JProgressBar progressBar;
// 2. Constructor call to ProgressBarDemo will
// create a object of JProgressBar and set
// minimum and maximum value of progress bar
// to 0 and 100
public ProgressBarDemo() {
progressBar = new JProgressBar();
progressBar.setMinimum(0);
progressBar.setMaximum(100);
// 3. Add Progress bar to Panel
add(progressBar);
}
// 4. progress method will update the value of
// progress bar every 100 ms after executing
// sleep method
public void progress(int value) {
progressBar.setValue(value);
}
public static void main(String args[]) {
// 5. Create a object of customized JPanel
final ProgressBarDemo progressBarDemo = new ProgressBarDemo();
// 6. Create a Object of JFrame and setting title as
// "Progress Bar Demo"
JFrame frame = new JFrame("Progress Bar Demo");
// Give frame a size in pixels as say 300,300
frame.setSize(200, 100);
// 7. set a operation when a user close the frame, here it
// closes the frame and exits the application
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// 8. Setting the Content Pane as ProgressBarDemo
frame.setContentPane(progressBarDemo);
// 9. Packing all the components together
frame.pack();
// 10. after setting contentPane, we make it
// visible on the frame by calling the method as
// setVisible and passing value as true.
frame.setVisible(true);
// 11. Having for loop which will loop from 0 to 100
// it will invoke a dedicated thread to Swing Component
// "JProgressBar" and on each loop will update the value
// of JProgressBar by 1. It will accomplish this by calling
// progressBarDemo.progress method and pass the updated or
// completed status to it.
for (int i = 0; i <= 100; i++) {
final int updateCompleted = i;
try {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
progressBarDemo.progress(updateCompleted);
}
});
// 12. Giving each loop a pause of 100 ms and
// updating JProgressBar meter by 1.
Thread.sleep(100);
} catch (InterruptedException e) {;}
}
}
}
Output of the program : 
