Java JFrame set default close operation to do-nothing-on-exit

import java.awt.FlowLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;

public class Main extends JFrame {
  public Main() {
    super("JButton");

    setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);
    setLayout(new FlowLayout());

    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.out.println("about to close");
      }/* w  ww.j a  va  2 s .  c  om*/
    });
  }

  public static void main(String[] args) {
    Main frame = new Main();
    frame.pack();
    frame.setVisible(true);
  }
}