How can I make a window popup here with swing?

Hi,

I am trying to make an app similar to the attached, where I have a menu bar.

When I click on an item in the menu bar, in this case Add Client,  how can I make the add client window will appear with the contents of that window? Can someone please just list list a little example?

Thanks!

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;

public class MenuExp extends JFrame {
   
    public MenuExp() {
       
        setTitle("Menu Example");
        setSize(1024, 768);
       
        // Creates a menubar for a JFrame
        JMenuBar menuBar = new JMenuBar();
       
        // Add the menubar to the frame
        setJMenuBar(menuBar);
       
        // Define and add two drop down menu to the menubar
        JMenu fileMenu = new JMenu("File");
       // JMenu editMenu = new JMenu("Edit");
        menuBar.add(fileMenu);
        //menuBar.add(editMenu);
       
        // Create and add simple menu item to one of the drop down menu
        JMenuItem addClientAction = new JMenuItem("Add Client");
        JMenuItem editClientAction = new JMenuItem("Edit Client");
        JMenuItem exitAction = new JMenuItem("Exit");
       


        fileMenu.add(addClientAction);
        fileMenu.add(editClientAction);
        fileMenu.addSeparator();
        fileMenu.add(exitAction);
        // Add a listener to the New menu item. actionPerformed() method will
        // invoked, if user triggred this menu item
        addClientAction.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                System.out.println("You have clicked on the add new client");
            }
        });
    }
    public static void main(String[] args) {
        MenuExp me = new MenuExp();
        me.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        me.setVisible(true);
    }
}