UI

import java.awt.Button;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;

import javax.swing.*;

public class MainClass {
    public static void addComponentsToPane(Container pane) {
        pane.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS));

        addAButton("Single player", pane);
        addAButton("Multy player", pane);
        addAButton("Controls", pane);
        addAButton("About", pane);
        addAButton("Exit", pane);
    }

    private static void addAButton(String text, Container container) {
        JButton button = new JButton(text);
        button.setAlignmentX(Component.CENTER_ALIGNMENT);
        container.add(button);
    }

    /*
     * Create the GUI and show it.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("Game frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Set up the content pane.
        addComponentsToPane(frame.getContentPane());
        //Display the window.
        frame.setSize(800, 800);
        frame.getContentPane().setBackground(Color.GREEN);
        frame.setTitle("Pong");
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}