Java JOptionPane ShowConfirmDialog

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import javax.swing.*;
import java.awt.event.*;

public class JavaJOptionPaneShowConfirmDialog extends WindowAdapter {

	JFrame f;

	JavaJOptionPaneShowConfirmDialog() {
		f = new JFrame();
		f.addWindowListener(this);
		f.setSize(300, 300);
		f.setLayout(null);
		f.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
		f.setVisible(true);
	}

	public void windowClosing(WindowEvent e) {
		int a = JOptionPane.showConfirmDialog(f, "Are you sure?");
		if (a == JOptionPane.YES_OPTION) {
			f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		}
	}

	public static void main(String[] args) {
		new JavaJOptionPaneShowConfirmDialog();
	}

}
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