import java.awt.BorderLayout;
import javax.swing.JButton;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.JOptionPane;
public class Main {
public static void main(String[] args) {
JDesktopPane dp = new JDesktopPane();
JInternalFrame inf = new JInternalFrame("Help", true, true, true,
true);
inf.setSize(200, 200);
inf.setVisible(true);
dp.add(inf);
JButton btn = new JButton("Click");
btn.addActionListener(e->JOptionPane.showInternalInputDialog(inf, "Hit me"));
inf.add(btn);
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setLayout(new BorderLayout());
f.add(dp);
f.setSize(400, 400);
f.setVisible(true);
}
}