Question

I’m trying to get get a vertical, top-aligned layout to work. This is what I have:

JPanel pane = new JPanel();
pane.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS));

MyImagePanel panelImage = new MyImagePanel();
panelImage.setSize(400, 400);

pane.add(new JComboBox());
pane.add(panelImage);
pane.add(new JButton("1"));
pane.add(new JButton("2"));
pane.add(new JButton("3"));

JFrame frame = new JFrame("Title");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(800, 600);
frame.add(pane);
frame.pack();
frame.setVisible(true);

All the controls appear, but it looks like padding is being applied at run time between their tops and bottoms so they’re somewhat vertically centered. This is what I’m going for:

-----------------------------------------------------
| ComboBox |                                        |
------------                                        |
|          |                                        |
| Image    |                                        |
|          |                                        |
------------                                        |
| Button 1 | Any additional space fills the right   |
------------                                        |
| Button 2 |                                        |
------------                                        |
| Button 3 |                                        |
------------                                        |
|                                                   |
|  Any additional space fills the bottom            |
|                                                   |
-----------------------------------------------------

How do I get BoxLayout to do that?

Thanks

————————- Update ————————-

Was able to use this:

Box vertical = Box.createVerticalBox();
frame.add(vertical, BorderLayout.NORTH);
vertical.add(new JComboBox());
vertical.add(new JButton("1"));  
...

to get what I wanted.

Answer 1

A more appropriate LayoutManager would be GridBagLayout, but there are other options:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test3 {

    protected static void initUI() {
        JPanel pane = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.anchor = GridBagConstraints.NORTHWEST;
        gbc.fill = GridBagConstraints.NONE;
        gbc.weightx = 0.0;
        gbc.weighty = 0.0;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        JPanel panelImage = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.RED);
                g.fillRect(0, 0, 400, 400);
            }
        };
        panelImage.setPreferredSize(new Dimension(400, 400));

        pane.add(new JComboBox(), gbc);
        pane.add(panelImage, gbc);
        pane.add(new JButton("1"), gbc);
        pane.add(new JButton("2"), gbc);
        // We give all the extra horizontal and vertical space to the last component
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        pane.add(new JButton("3"), gbc);

        JFrame frame = new JFrame("Title");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(pane);
        frame.pack();
        frame.setVisible(true);

    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                initUI();
            }
        });
    }
}