Java JFrame set appropriate size via pack()

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

public class Main { 
    public static void main(String[] args) { 
        JFrame frame = new JFrame("Adding Components to JFrame"); 
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        Container contentPane = frame.getContentPane(); 
        // Add a Close button 
        JButton closeButton = new JButton("Close"); 
        contentPane.add(closeButton); /*from   w  w w. jav  a  2 s.  c  o  m*/

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