In Java, JProgressBar is a Swing component that provides visual feedback to the user about the progress of a long-running operation. It can be used to display the progress of a file download, an installation process, or any other long-running task.

Here is an example of how to use JProgressBar:

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

public class ProgressBarExample extends JFrame implements ActionListener {
    private JProgressBar progressBar;
    private JButton startButton;
    private Timer timer;
    private int progress;

    public ProgressBarExample() {
        progressBar = new JProgressBar(0, 100);
        progressBar.setValue(0);
        progressBar.setStringPainted(true);

        startButton = new JButton("Start");
        startButton.addActionListener(this);

        JPanel panel = new JPanel(new BorderLayout());
        panel.add(progressBar, BorderLayout.CENTER);
        panel.add(startButton, BorderLayout.SOUTH);

        setContentPane(panel);
        setSize(300, 100);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);

        timer = new Timer(100, this);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == startButton) {
            startButton.setEnabled(false);
            timer.start();
        } else if (e.getSource() == timer) {
            progress += 5;
            if (progress > 100) {
                progress = 0;
                startButton.setEnabled(true);
                timer.stop();
            }
            progressBar.setValue(progress);
        }
    }

    public static void main(String[] args) {
        new ProgressBarExample();
    }
}

In this example, a JProgressBar is created with a minimum value of 0 and a maximum value of 100. The StringPainted property is set to true to display the progress percentage as text on the progress bar. A JButton is also created to start the progress.

When the user clicks the "Start" button, the button is disabled and a Timer is started with an interval of 100 milliseconds. The timer increments the progress value by 5 every 100 milliseconds until it reaches 100, at which point the progress bar is reset to 0 and the "Start" button is re-enabled.

This is just a basic example, but JProgressBar can be used in many different ways to provide visual feedback to the user about the progress of long-running tasks.