Java - Problemas en la optimización de mi código

public class BotonX extends JButton implements ActionListener {

	public BotonX(String num) {

		super(num);

		setPreferredSize(new Dimension(50, 30));

		addActionListener(this);

	}

	@Override

	public void actionPerformed(ActionEvent e) {

		setText("X");

	}

}

public class Prueba extends JFrame {

	private BotonX[] botonera;

	public Prueba() {

		botonera = new BotonX[9];

		JPanel pnBotones = new JPanel();

		pnBotones.setLayout(new GridLayout(1,9,5,5));

		for (int i = 0; i < 9; i++) {

			botonera[i] = new BotonX(Integer.toString(i+1));

			pnBotones.add(botonera[i]);

		}

		pnBotones.setBorder(new EmptyBorder(15,15,15,15));

		setContentPane(pnBotones);

		setTitle("Prueba Botones");

		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		pack();

		setLocationRelativeTo(null);

		setVisible(true);

	}

	public static void main(String[] args) {

		SwingUtilities.invokeLater(new Runnable() {

			@Override

			public void run() {

				new Prueba();

			}

		});

	}

}