Unexplained indentation after JComboBox

Question

Hey folks,
I've got a bit of an odd problem here, which is either because of my ignorance of JComboBox behaviour or simply an odd bug or feature in said JComboBox component.
Basically, I've got an Options window that, in my application, is opened using a JOptionPane. (So it's a Dialog instead of a Frame.) In this Options window, I've got a JPanel (holder) that holds another JPanel (copying). This JPanel holds another JPanel (bufferSize) and two JCheckBoxes. In the last JPanel (bufferSize) is a JLabel and a JComboBox.
The problem lies with the JComboBox; below the JComboBox come the two JCheckBoxes that now have, unexplicably, an indentation of about 100 pixels. Below I've added the simplified code of the problem. If you guys want to see it for yourself, create three Java files with the said class names and run the ComboExample.java file. (It's the one with the main method... ;))
So, essentially; any of you have a clue what's causing this indentation? More information available in the form of comments in the code. I've also got an email subscription to this thread, so feel free to ask any questions about the code and supply me with suggestions. I'll try to reply as soon as I get the email.. ;)
import javax.swing.JFrame;
public class ComboExample{
     public static void main(String args[]){
          GUI gui = new GUI();
          gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          gui.setSize(350, 75);
          gui.setTitle("Example app; opening the options menu");
          gui.setVisible(true);
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class GUI extends JFrame implements ActionListener{
     private JButton buttonOpenDialog;
     // Constructor; creates button, adds actionlistener and adds button to frame
     public GUI(){
          buttonOpenDialog = new JButton("Open the new dialog!");
          buttonOpenDialog.addActionListener(this);
          add(buttonOpenDialog);
     // Mandatory method that controls what happens when the button's pressed
     // (When pressed: new window opens called Options)
     public void actionPerformed(ActionEvent e) {
          if(e.getSource() == buttonOpenDialog){
               Options options = new Options();
               JOptionPane.showMessageDialog(null, options, "Options menu", JOptionPane.PLAIN_MESSAGE);
import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.*;
import javax.swing.border.TitledBorder;
public class Options extends JPanel{
     private JCheckBox showCopyOverview;
     private JCheckBox showCopyErrorMessages;
     private JComboBox bufferSize;
     // Constructor calls createInterface method
     public Options(){
          createInterface();
      * Creates the interface. First a holder panel is created that uses a BorderLayout.
      * This is done for future implementations. Then there's a copying panel with its own
      * border and text on border. This panel uses a Vertical (Y_AXIS) BoxLayout. To these
      * the various options are added. Lastly, the Combobox is on its own panel so that
      * the label can appear next to it. This panel also uses a BoxLayout, but then a horizontal
      * (X_AXIS) variant.
      * My question now is; why do the two checkboxes below the JComboBox and JLabel have
      * that indentation that they do? I never tell them to do that.
      * Solutions tried:
      * - Setting a maximum size (setMaximumSize())
      * - Removing the JComboBox (worked partially; the indentation became smaller)
      * - Removing the JLabel (worked partially, see above)
      * - Removing the bufferSizePanel but leaving the JLabel and JComboBox
      * - Removing the bufferSizePanel, JLabel and JComboBox (works, but evidently not desired)
      * - Putting the two JCheckBoxes on a different JPanel
      * - Suggestions... ?
     public void createInterface(){
          // First create all the required panels
          JPanel panelHolder = new JPanel();
          panelHolder.setLayout(new BorderLayout());
          JPanel panelCopying = new JPanel();
          panelCopying.setLayout(new BoxLayout(panelCopying, BoxLayout.Y_AXIS));
          TitledBorder borderCopying = BorderFactory.createTitledBorder("Copying options");
          panelCopying.setBorder(borderCopying);
          JPanel panelBufferSize = new JPanel();
          panelBufferSize.setLayout(new BoxLayout(panelBufferSize, BoxLayout.X_AXIS));
          // Create all the elements that will inhabit the panels
          showCopyOverview = new JCheckBox("Option 1");
          showCopyErrorMessages = new JCheckBox("Option 2");
          JLabel labelBufferSize = new JLabel("Option 3: ");
          bufferSize = new JComboBox();
          bufferSize.setMaximumSize(new Dimension(65, 25));
          // Add all the elements to their respective panels
          panelBufferSize.add(labelBufferSize);
          panelBufferSize.add(bufferSize);
          panelCopying.add(panelBufferSize);
          panelCopying.add(showCopyOverview);
          panelCopying.add(showCopyErrorMessages);
          panelHolder.add(panelCopying, BorderLayout.CENTER);
          add(panelHolder);
}Edited by: SEThorian on Dec 4, 2008 1:35 PM

Answer 1

You are looking for JComponent#setAlignmentX(float).
[How to Use BoxLayout (The Java™ Tutorials > Creating a GUI with JFC/Swing > Laying Out Components Within a Container)|http://java.sun.com/docs/books/tutorial/uiswing/layout/box.html]
import java.awt.*;
import javax.swing.*;
public class ComboExample{
    public static void main(String[] args) {
        JOptionPane.showMessageDialog(null, new Options(),
                      "Options menu", JOptionPane.PLAIN_MESSAGE);
class Options extends JPanel{
    private JCheckBox showCopyOverview;
    private JCheckBox showCopyErrorMessages;
    private JComboBox bufferSize;
    public Options(){
        super(new BorderLayout());
        createInterface();
    public void createInterface(){
        bufferSize             = new JComboBox();
        showCopyOverview       = new JCheckBox("Option 1");
        showCopyErrorMessages  = new JCheckBox("Option 2");
        JPanel panelBufferSize = new JPanel(new BorderLayout());
        panelBufferSize.add(new JLabel("Option 3: "), BorderLayout.WEST);
        panelBufferSize.add(bufferSize);
        Box panelCopying = Box.createVerticalBox();
        panelCopying.setBorder(
           BorderFactory.createTitledBorder("Copying options"));
        panelCopying.add(panelBufferSize);
        panelCopying.add(showCopyOverview);
        panelCopying.add(showCopyErrorMessages);
        panelBufferSize.setAlignmentX(Component.LEFT_ALIGNMENT);
        showCopyOverview.setAlignmentX(Component.LEFT_ALIGNMENT);
        showCopyErrorMessages.setAlignmentX(Component.LEFT_ALIGNMENT);
        add(panelCopying);
}