Java Box.createRigidArea(Dimension d)

public static Component createRigidArea(Dimension d)

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
//from   w  w w . j  av a  2s.  c om
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;

public class Main {
  public static void main(String args[]) {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Box rowOne = new Box(BoxLayout.Y_AXIS);
    rowOne.add(new JLabel("Username"));
    rowOne.add(Box.createRigidArea(new Dimension(20,20)));
    
    rowOne.add(new JTextField());
    Component rowTwo = Box.createVerticalStrut(2);
    
    f.add(rowOne, BorderLayout.NORTH);
    f.add(rowTwo, BorderLayout.SOUTH);
    f.setSize(300, 200);
    f.setVisible(true);
  }
}