Java SpringLayout set constraint

import javax.swing.JFrame; 
import java.awt.Container; 
import javax.swing.SpringLayout; 
import javax.swing.JButton; 

public class Main { 
    public static void main(String[] args) { 
        JFrame frame = new JFrame("SpringLayout2"); 
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        Container contentPane = frame.getContentPane(); 

        // Set the content pane's layout to a SpringLayout 
        SpringLayout springLayout = new SpringLayout(); 
        contentPane.setLayout(springLayout); 

        // Create two JButtons 
        JButton b1 = new JButton("Button 1"); 
        JButton b2 = new JButton("Little Bigger Button 2"); 

        // Add two JButtons without using any constraints 
        contentPane.add(b1); /*  w w  w  .  j a  v  a  2s  .c  o  m*/
        contentPane.add(b2); 

        // Now add constraints to both JButtons 
        // Set x for b1 as 10 
        springLayout.putConstraint(SpringLayout.WEST, b1, 10, 
                                   SpringLayout.WEST, contentPane); 
        // Set y for b1 as 20 
        springLayout.putConstraint(SpringLayout.NORTH, b1, 20, 
                                   SpringLayout.NORTH, contentPane); 

        // Set x for b2 as 10 from the right edge of b1 
        springLayout.putConstraint(SpringLayout.WEST, b2, 10, 
                                   SpringLayout.EAST, b1); 
        // Set y for b1 as 20 
        springLayout.putConstraint(SpringLayout.NORTH, b2, 20, 
                                   SpringLayout.NORTH, contentPane); 

        /* set height and width for the content pane as the bottom 
           edge of b1 + 10 and right edge of b2 + 10. 
         */ 

        // Set the bottom edge of the content pane  
        springLayout.putConstraint(SpringLayout.SOUTH, contentPane, 10, 
                                   SpringLayout.SOUTH, b1); 

        // Set the right edge of the content pane 
        springLayout.putConstraint(SpringLayout.EAST, contentPane, 10, 
                                   SpringLayout.EAST, b2); 

        frame.pack(); 
        frame.setVisible(true); 
    } 
}