Jax's crappy menu

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

import java.awt.Font;

import javax.swing.SwingUtilities;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;


public class GameMainMenu extends JFrame implements ActionListener{


    JButton play, difficulty, credits;

    GameMainMenu(String title){

        super(title);
        this.setSize(2000,1000);
        this.init();
        this.setVisible(true);
        }

    void init(){

        JFrame f = new JFrame();

        JLabel lmainMenu = new JLabel("Attack of the Squares");
        lmainMenu.setFont(new Font("Undercover", Font.BOLD, 85));
        JPanel panel = new JPanel();
        panel.add(lmainMenu);
        JPanel game = new JPanel();
        game.setVisible(false);
        f.add(panel);
        f.add(game);
        play = new JButton("Play");
        difficulty = new JButton("Difficulty");
        credits = new JButton("Credits");

        play.setPreferredSize(new Dimension(100, 50));
        play.setBackground(Color.green);

        difficulty.setPreferredSize(new Dimension(100, 50));
        difficulty.setBackground(Color.green);

        credits.setPreferredSize(new Dimension(100, 50));
        credits.setBackground(Color.green);

        panel.add(play);
         panel.add(difficulty);
         panel.add(credits);
         play.addActionListener(this);
         difficulty.addActionListener(this);
         credits.addActionListener(this);
         panel.setBackground(new Color(204, 255, 51));
         this.add(panel);

    }


    public void actionPerformed(ActionEvent event) {

        if(event.getSource() == credits){
            JOptionPane.showMessageDialog(this, "Attack of the Squares was developed by Bryan, Jax, and Will");

        }
        if(event.getSource() == play){
            JOptionPane.showMessageDialog(this, "You thought ;)");
    }

        if(event.getSource() == difficulty){
            JOptionPane.showMessageDialog(this, "Just press 9");

        }



    }






}