Swing display time (click once to display once)

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

public class SwingDemo
{
    
    private static void createGUI()
    {
    
        MyFrame frame = new MyFrame("Swing Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);



        frame.setSize(400, 300);
        frame.setVisible(true);
    }

    public static void main(String[] args)
    {
    
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
    
            public void run()
            {
    
                createGUI();
            }
        });

    }
}

import javax.swing.*;
import javax.swing.plaf.multi.MultiButtonUI;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.SimpleTimeZone;

public class MyFrame extends JFrame {
    
    JLabel timetable = new JLabel("00:00:00");
    JButton button = new JButton(" Display time ");
    public MyFrame(String swing_demo) {
    
        super(swing_demo);
        // Content panel 
        Container contenePane = getContentPane();
        contenePane.setLayout(new FlowLayout());
        // Add components to the content panel 
        contenePane.add(button);
        contenePane.add(timetable);
        //contenePane.add(new JButton(" test 2"));
        // Create a listener object 
        MyButtonListener listener = new MyButtonListener();
        button.addActionListener(listener);
    }
    //ActionListener  It's a interface
    private class MyButtonListener implements ActionListener{
    
        public void actionPerformed(ActionEvent e){
    
            // When the button is clicked ,Swing The framework will automatically call the listener actionPerformed() Method 
            System.out.println(" Button clicked ...");
            MyFrame.this.showtime();
        }

    }
    public void showtime(){
    
        SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
        String timetr = sdf.format(new Date());
        timetable.setText(timetr);
    }
}