Java Swing BoxLayout add rigid area

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {

   public static void main(String[] args) {
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setTitle("BoxLayout frame");

      frame.getContentPane().setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.PAGE_AXIS));

      frame.getContentPane().add(Box.createRigidArea(new Dimension(50, 50)));
      frame.getContentPane().add(makePanel(Color.red, 10, Component.CENTER_ALIGNMENT));
      frame.getContentPane().add(Box.createVerticalGlue());
      frame.getContentPane().add(makePanel(Color.blue, 50, Component.LEFT_ALIGNMENT));
      frame.getContentPane().add(Box.createVerticalGlue());
      frame.getContentPane().add(makePanel(Color.yellow, 100, Component.RIGHT_ALIGNMENT));
      frame.getContentPane().add(Box.createVerticalGlue());
      frame.getContentPane().add(makePanel(Color.green, 200, Component.LEFT_ALIGNMENT));
      frame.getContentPane().add(Box.createVerticalGlue());
      frame.getContentPane().add(makePanel(Color.pink, 500, Component.CENTER_ALIGNMENT));

      frame.pack();//  ww  w .  j  ava2 s  .  c  om
      frame.setVisible(true);
   }

   private static JPanel makePanel(Color col, int w, float a) {
      JPanel panel = new JPanel();
      panel.setBackground(col);
      panel.setAlignmentX(a);
      panel.setPreferredSize(new Dimension(w, 50));
      panel.setMaximumSize(panel.getPreferredSize());
      panel.setMinimumSize(panel.getPreferredSize());
      return panel;
   }
}