Probleme d'un JFrame.dispose();

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

JButton M1,M2,M3;

JFrame Menu;

class GestionClic implements ActionListener {
   public void actionPerformed(ActionEvent e) {
    if (e.getSource()==M1){
    Menu.dispose();
   }else if(e.getSource()==M2){
    Menu.dispose();
   }else if(e.getSource()==M3){
    Menu.dispose();
   }
   }
}

void main() {
   JFrame Menu = new JFrame("Menu");
   Menu.setVisible(true);
   Menu.setLocationRelativeTo(null);
   Menu.setSize(500, 500);
   Menu.setLocationRelativeTo(null);
   GestionClic GC = new GestionClic();
   M1 = new JButton("Solo");
   M2 = new JButton("Multi");
   M3 = new JButton("Quitter");
   Menu.add(M1);
   M1.addActionListener(GC);
   Menu.add(M2);
   M2.addActionListener(GC);
   Menu.add(M3);
   M3.addActionListener(GC);
   GridLayout GL = new GridLayout();
   GL.setColumns(0);
   GL.setRows(3);
   Menu.setLayout(GL);
}