JOptionPane is a class in Java Swing that provides a simple way to create pop-up dialogs. It can be used to display information, prompt for input, or ask for confirmation from the user.

Here is an example of how to use JOptionPane to display a simple message dialog:

import javax.swing.JOptionPane;

public class JOptionPaneExample {

    public static void main(String[] args) {
        JOptionPane.showMessageDialog(null, "Hello, world!");
    }
}

This will display a dialog with the message "Hello, world!" and an OK button for the user to dismiss the dialog.

JOptionPane also provides methods for displaying input dialogs to get user input, confirm dialogs to ask for confirmation from the user, and option dialogs to present the user with a set of options to choose from.

Here is an example of how to use JOptionPane to display an input dialog and retrieve the user's input:

import javax.swing.JOptionPane;

public class JOptionPaneExample {

    public static void main(String[] args) {
        String name = JOptionPane.showInputDialog(null, "What is your name?");
        JOptionPane.showMessageDialog(null, "Hello, " + name + "!");
    }
}

This will display a dialog with a prompt for the user to enter their name, and then display a greeting with their name.