javax display error message dialog

import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class JOptionPaneERROR_MESSAGE {

  public static void main(String[] args) {
    //create new Jpannel
    final JPanel panel = new JPanel();

    JOptionPane.showMessageDialog(panel, 
           "Could not open file", "Error", JOptionPane.ERROR_MESSAGE);
    

  }