Ajouter des éléments à un bouton java

import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 

import javax.swing.JButton; 
import javax.swing.JFrame; 
import javax.swing.JOptionPane; 

class MaFenetre extends JFrame  
{  
    private static final long serialVersionUID = 1; 
     
    private final JButton MonBouton ;  

    public MaFenetre ()  
    {  
        setLayout(null); 
        setTitle("Menu principal") ;  
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        setBounds(10,40,300,200) ; 
         
        MonBouton = new JButton("Addition") ;  
        MonBouton.setSize(100, 20); 
        MonBouton.addActionListener(new ActionListener () 
        { 
            @Override 
            public void actionPerformed(ActionEvent e) 
            { 
                JOptionPane.showMessageDialog(null,"Clic !!!"); 
            } 
        }); 
         
        add(MonBouton) ;  
    }  
}  

public class MonProg 
{  
    public static void main(String args[]) 
    {  
        new MaFenetre().setVisible(true) ;  
    }  
}