Components moving on setVisible

Question

I have a function that creates a JPanel with some Components (a few JLabels, JTextFields, and a JButton). When the button is clicked, it may or may not cause one of the JLabels that was previously set to be invisible to be visible using Component.setVisible( true or false ).
I found that whenever the JLabel was set to become visible, it caused all the other Components to move down about 20 pixels. Why did this happen, and what am I supposed to do about it?
Here is a code example that shows what I mean. On the system I'm coding it on (Windows with JDK 1.3.1) clicking the button causes everything in the JPanel to move down.
JPanel makeStartPane()
     JPanel panel = new JPanel() ;
     panel.setLayout( null ) ;
     panel.setSize( width, height ) ;
     panel.setLocation( 0, 0 ) ;
     JLabel label1 = new JLabel( "some text" ) ;
     label1.setSize( 75, 18 ) ;
     label1.setLocation( 5, 30 ) ;
     panel.add( label1 ) ;
     JLabel label2 = new JLabel( "some more text" ) ;
     label2.setSize( 100, 18 ) ;
     label2.setLocation( 5, 50 ) ;
     label2.setVisible( false ) ;       // this one starts off invisible
     panel.add( label2 ) ;
     JButton button = new JButton( "click me" ) ;
     button.setSize( 90, 25 ) ;
     button.setLocation( 5, 75 ) ;
     panel.add( button ) ;
     button.addActionListener( new ActionListener()
          public void actionPerformed( ActionEvent e )
               // set to visible here
               getContentPane().getComponent( 1 ).setVisible( true ) ;
     return panel ;
setContentPane( makeStartPane() ) ; // set the current pane to the start pane

Answer 1

I done this small test, and it look ok:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Tjf extends JFrame 
public Tjf()
     super();
     setBounds(6,6,400,300);     
     addWindowListener(new WindowAdapter()
    {     public void windowClosing(WindowEvent ev)
               dispose();     
               System.exit(0);
     setContentPane(makeStartPane());
     MenuBar mb   = new MenuBar();
          Menu mm      = new Menu("Option");
     MenuItem mi  = new MenuItem("New");
       mb.add(mm);
     mm.add(mi);
     setMenuBar(mb);
     setVisible(true);     
public JPanel makeStartPane()
     JPanel panel = new JPanel();
     panel.setLayout(null);
//     panel.setSize(200,200);
     panel.setLocation(0,0);
     JLabel label1 = new JLabel("some text");
     label1.setSize(75,18) ;
     label1.setLocation(5,30);
     panel.add(label1);     
     JLabel label2 = new JLabel("some more text") ;
     label2.setSize(100,18 ) ;
     label2.setLocation(5,50 ) ;
     label2.setVisible(false) ;
// this one starts off invisible
     panel.add(label2) ;     
     JButton button = new JButton("click me");     
     button.setSize(90,25);     
     button.setLocation(5,75);
     panel.add(button);
     button.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               getContentPane().getComponent(1).setVisible(true);     
     return(panel);
public static void main (String[] args)
     new Tjf();  
}       Noah
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Tjf extends JFrame
public Tjf()
     super();
     setBounds(6,6,400,300);     
     addWindowListener(new WindowAdapter()
{     public void windowClosing(WindowEvent ev)
               dispose();
               System.exit(0);
     setContentPane(makeStartPane());
     MenuBar mb = new MenuBar();
Menu mm = new Menu("Option");
     MenuItem mi = new MenuItem("New");
     mb.add(mm);
     mm.add(mi);
     setMenuBar(mb);
     setVisible(true);     
public JPanel makeStartPane()
     JPanel panel = new JPanel();
     panel.setLayout(null);
//     panel.setSize(200,200);
     panel.setLocation(0,0);
     JLabel label1 = new JLabel("some text");
     label1.setSize(75,18) ;
     label1.setLocation(5,30);
     panel.add(label1);     
     JLabel label2 = new JLabel("some more text") ;
     label2.setSize(100,18 ) ;
     label2.setLocation(5,50 ) ;
     label2.setVisible(false) ;
// this one starts off invisible
     panel.add(label2) ;     
     JButton button = new JButton("click me");     
     button.setSize(90,25);     
     button.setLocation(5,75);
     panel.add(button);
     button.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               getContentPane().getComponent(1).setVisible(true);     
     return(panel);
public static void main (String[] args)
     new Tjf();