Java Swing Boxlayout: having panels of different sizes (ratio to each other)

Question

I'm trying to create a boxlayout panel with 2 other panels inside it, one of which is only half the size of the other (so a ratio of 1/3 to 2/3). Setting preferred size doesn't seem to work and I've been unable to figure out any other way (the following code was mainly generated with Windowbuilder, so apologies if it's a bit of a mess):

public class GUIControls extends JFrame implements IGUIControls {
    private JTextField textField;

    private int posX=0,posY=0;

    public GUIControls() {

        getContentPane().setBackground(Color.WHITE);
        getContentPane().setLayout(new CardLayout(0, 0));

        JPanel rootPanel = new JPanel();
        rootPanel.setBorder(new LineBorder(new Color(0, 0, 255), 1, true));
        rootPanel.setBackground(Color.WHITE);
        getContentPane().add(rootPanel, "name_25253210045969");
        rootPanel.setLayout(new BoxLayout(rootPanel, BoxLayout.X_AXIS));
        rootPanel.setPreferredSize(new Dimension(600, 400));

        JPanel menuLeft = new JPanel();
        rootPanel.add(menuLeft);
        menuLeft.setBackground(Color.WHITE);
        menuLeft.setLayout(null);
        menuLeft.setPreferredSize(new Dimension((1/3)*rootPanel.getWidth(), rootPanel.getHeight()));

        JPanel contentRight = new JPanel();
        rootPanel.add(contentRight);
        contentRight.setBackground(Color.WHITE);
        contentRight.setPreferredSize(new Dimension((2/3)*rootPanel.getWidth(), rootPanel.getHeight()));
        contentRight.addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent arg0) {
                CardLayout cardLayout = (CardLayout) getContentPane().getLayout();
                cardLayout.show(getContentPane(), "name_36737116256884");
            }
        });
        contentRight.setLayout(null);

        setUndecorated(true);   

        addMouseListener(new MouseAdapter()
        {
           public void mousePressed(MouseEvent e)
           {
              posX=e.getX();
              posY=e.getY();
           }
        });

        addMouseMotionListener(new MouseAdapter()
        {
             public void mouseDragged(MouseEvent evt)
             {
                //sets frame position when mouse dragged            
                setLocation (evt.getXOnScreen()-posX,evt.getYOnScreen()-posY);

             }
        });

    }

    public void runGUI(){
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                GUIControls guiControls = new GUIControls();
                guiControls.pack();
                guiControls.setLocationRelativeTo(null);
                guiControls.setSize(600, 400);
                guiControls.setVisible(true);
            }
        });
    }
}

Does anyone know how I'd go about doing this?

Thanks.

Answer 1

You could try using the GridBagLayout. Read the section from the Swing tutorial on How to Use GridBagLayout for more information. I would guess you would need to play with the weightx property.

Or you could use the Relative Layout which was specifically designed to do this.

Edit:

Did you do any debugging? What happens when you add:

System.out.println(menuLeft.getPreferredSize());
System.out.println(contentRight.getPreferredSize());

You have two problems:

1. What is the value of 1/3? You need to fix your size calculation.
2. What is the size of your rootPanel? A component doesn't have a size until the component is displayed on the visible GUI. You set the preferred size of the component.