Make bottom panel in Borderlayout to expand like center panel

Question

So it's a pretty simple problem, but I can't find a simple way to implement it. I basically have 3 instances of JPanel: north, south and center. Normally, if you play with window height, the center panel will be variable. What I would like, is to have the south panel height being variable instead of the center one.

Here is the code:

public class TestCode {

public static void main(String[] args) {

    JFrame window = new JFrame("Test");
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setSize(300, 300);

    JPanel panelUp = new JPanel();
    JPanel panelCenter = new JPanel();
    JPanel panelDown = new JPanel();

    window.add(panelUp, BorderLayout.NORTH);
    window.add(panelCenter, BorderLayout.CENTER);
    window.add(panelDown, BorderLayout.SOUTH);

    panelUp.setBackground(new Color(200, 240, 200));
    panelCenter.setBackground(new Color(240, 200, 200));
    panelDown.setBackground(new Color(200, 200, 240));

    panelUp.setPreferredSize(new Dimension(panelUp.getWidth(), 50));
    panelCenter.setPreferredSize(new Dimension(panelCenter.getWidth(), 100));
    panelDown.setPreferredSize(new Dimension(panelDown.getWidth(), window.getHeight() - 150));

    window.setVisible(true);
}

}

Answer 1

Simply add the top and center into a panel that is itself a border layout :

public static void main(String[] args) {

    JFrame window = new JFrame("Test");
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setSize(300, 300);


    JPanel innerPanel = new JPanel(new BorderLayout());


    JPanel panelUp = new JPanel();
    JPanel panelCenter = new JPanel();
    JPanel panelDown = new JPanel();

    window.add(innerPanel, BorderLayout.NORTH);
    window.add(panelDown, BorderLayout.CENTER);

    innerPanel.add(panelUp, BorderLayout.NORTH);
    innerPanel.add(panelCenter, BorderLayout.SOUTH);

    panelUp.setBackground(new Color(200, 240, 200));
    panelCenter.setBackground(new Color(240, 200, 200));
    panelDown.setBackground(new Color(200, 200, 240));

    panelUp.setPreferredSize(new Dimension(panelUp.getWidth(), 50));
    panelCenter.setPreferredSize(new Dimension(panelCenter.getWidth(), 100));
    panelDown.setPreferredSize(new Dimension(panelDown.getWidth(), window.getHeight() - 150));

    window.setVisible(true);
}

This code should do exactly what you want while hardly altering the code

Answer 2

***************BorderLayout************************
*  ********BorderLayout*in*PAGE_START************ *
*  *                                            * *
*  *   Component in PAGE_START                  * *
*  *                                            * *
*  *   Component in PAGE_END                    * *
*  *                                            * *
*  ********************************************** *
*                                                 *
*      Component in CENTER                        *
*                                                 *
***************************************************

See the Nested Layout Example for more ideas about how to combine layouts to create the required layout.

Answer 3

What I would like, is to have the south panel height being variable instead of the center one.

• not possible with BorderLayout, without listening for JFrame from ComponentListener, recalculating for PreferredSize and then to call JFrame.revalidate() and JFrame.repaint(),

• use proper LayoutManager

  1. GridBagLayout

  2. SpingLayout by @aterai

  3. custom MigLayout, TableLayout

Answer 4

Have you tried setting the maximum size (setMaximumSize) for the north and center panel? Or perhaps setSize directly.