Выход из оконного приложения

package easybudda.examples.closebutton;
 
import java.awt.event.*;
import javax.swing.*;
 
public class CloseButtonExample {
    private JFrame frmMain;
    private JButton btnExit;
    
    CloseButtonExample() {
        frmMain = new JFrame("Close button example");
        frmMain.setSize(200, 100);
        frmMain.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        btnExit = new JButton("Exit");
        btnExit.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                frmMain.dispose();
            }
        });
        
        frmMain.add(btnExit);
        frmMain.setVisible(true);
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new CloseButtonExample();
            }
        });
 
    }
 
}

frmMain.dispose();

Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(new WindowEvent(frmMain, WindowEvent.WINDOW_CLOSING));

frmMain.dispatchEvent(new WindowEvent(frmMain, WindowEvent.WINDOW_CLOSING));

 System.exit()

frmMain.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frmMain.dispatchEvent(new WindowEvent(frmMain, WindowEvent.WINDOW_CLOSING));

Runtime.getRuntime().addShutdownHook(new Thread());

frmMain.dispatchEvent(new WindowEvent(frmMain, WindowEvent.WINDOW_CLOSING));