Java CardLayout .preferredLayoutSize (Container parent)

public Dimension preferredLayoutSize(Container parent)

//from   w w w.  j  a va2  s. c o  m
import java.awt.CardLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {

  public static void main(String[] args) {
    JFrame aWindow = new JFrame();
    aWindow.setSize(400, 400);
    aWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    aWindow.add(new CardLayoutPanel());
    aWindow.setVisible(true);
  }
}

class CardLayoutPanel extends JPanel implements ActionListener {
  CardLayout card = new CardLayout(50, 50);

  public CardLayoutPanel() {
    setLayout(card);
    JButton button;
    for (int i = 1; i <= 6; i++) {
      add(button = new JButton("Press " + i), "Card" + i);
      button.addActionListener(this);
    }
    System.out.println(card.preferredLayoutSize(this));
  }
  public void actionPerformed(ActionEvent e) {
    card.next(this);
  }
}