IllegalArgumentException in a JTabbedPane

Question

Hi,
I am creating a pane that has several tabs. I receive an IllegalArgumentException which is telling me I cannot add a window to a container. Here is part of my code (not all of it, just the relevant parts, called "Preguard," which I am working on now) and I would appreciate any help in determining what I am doing wrong.
TIA,
Jeff
import javax.swing.JFrame;
public class MailGenBuilder
private String actions[] = { " ", "REMOVE", "STATUS", "SYNCH", "UPDATE" };
private JFrame preguardFrame = new JFrame();
public MailGenBuilder()
public MailGen construct()
// create the controls for preguardFrame
JLabel preguardActionLabel = new JLabel( "SELECT ACTION" );
preguardActionLabel.setHorizontalAlignment( JLabel.CENTER );
// I'm not including the dimensions in this post (similar for a few lines down, also)
preguardActionLabel.setPreferredSize( new Dimension( /*x, x*/ ) );
JComboBox preguardActionComboBox = new JComboBox( actions );
preguardActionComboBox.setBorder( BorderFactory.createLineBorder(
    Color.BLACK, 1 ) );
preguardActionComboBox.setPreferredSize( new Dimension( /*x, x*/ ) );
// create the SEND and CANCEL buttons
JButton preguardSendButton = new JButton( "SEND STATUS" );
preguardSendButton.setBackground( Color.white );
preguardSendButton.setBorder( raisedBevel );
JButton preguardCancelButton = new JButton( "CANCEL" );
preguardCancelButton.setBackground( Color.white );
preguardCancelButton.setBorder( raisedBevel );
preguardFrame.getContentPane().setLayout( null );
preguardFrame.getContentPane().add( preguardActionLabel );
preguardFrame.getContentPane().add( preguardActionComboBox );
preguardFrame.getContentPane().add( preguardSendButton );
preguardFrame.getContentPane().add( preguardCancelButton );
// add the various panels to the tabbed pane
JTabbedPane pane = new JTabbedPane();
// the exception is thrown on the next line
pane.add( "PREGUARD", preguardFrame );
pane.add( /*second pane*/ );
pane.add( /*third pane*/ );
pane.add( /*fourth pane*/ );

Answer 1

You define preguardFrame as a JFrame which is a top level container, when you try to add it to a JTabbedFrame the above Exception is throw. Try making preguardFrame a JPanel.
Also setting preguardFrame layout to null and then adding several components will probably not give you the result you want.
Cheers
DB