Java Swing GridBagLayout not as expected

Question

Some how I can't get gridwidth to work in GridBagLayout in my simple SwingApp.

I have this code in Java Swing:

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.Border;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;

class GridBagLayt extends JFrame {
 
    GridBagLayt()
    {
        JButton jb1 = new JButton("1");
        JButton jb2 = new JButton("2");
        JButton jb3 = new JButton("3");
        JButton jb4 = new JButton("4");
        JButton jb5 = new JButton("5");
        
        GridBagLayout lay = new GridBagLayout();
        GridBagConstraints cons = new GridBagConstraints();
        
        setLayout(lay);
        cons.fill = GridBagConstraints.BOTH;
        cons.gridheight = 1;
        cons.weightx = 1;
        cons.weighty = 1;


        cons.gridx = 0; cons.gridy = 0; 
        cons.gridwidth = 2;
        lay.setConstraints(jb1, cons);
        add(jb1);
        
        cons.gridx = 2; 
        lay.setConstraints(jb2, cons);
        add(jb2);
         
        cons.gridx = 0; cons.gridy = 1; 
        cons.gridwidth = 1;
        lay.setConstraints(jb3, cons);
        add(jb3);
        
        cons.gridx = 1;
        cons.gridwidth = 2;
        lay.setConstraints(jb4, cons);
        add(jb4);
        
        cons.gridx = 3;
        cons.gridwidth = 1;
        lay.setConstraints(jb5, cons);
        add(jb5);
        
        
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(700,200);
        setVisible(true);
    }
  }

    public class SwingApp {
 
        public static void main(String[] args) {
     
            new GridBagLayt();
        }
    }

This is what I want to get:

But instead I get this:

I really don't know what the problem is, the coordinate and gridwidth seems ok to me, and I expected this to work, but it's not. And if I add four more buttons between this two rows, then the third row seems OK, but I don't want that:

Example: If I add this code

cons.gridx = 0; cons.gridy = 0; 
        cons.gridwidth = 2;
        lay.setConstraints(jb1, cons);
        add(jb1);
        
        cons.gridx = 2; 
        lay.setConstraints(jb2, cons);
        add(jb2);
        
        
        cons.gridx = 0; cons.gridy = 1; 
        cons.gridwidth = 1;
        lay.setConstraints(jb3, cons);
        add(jb3);
        
        cons.gridx = 1;
        lay.setConstraints(jb4, cons);
        add(jb4);
        
        cons.gridx = 2;
        lay.setConstraints(jb5, cons);
        add(jb5);
      
        cons.gridx = 3;
        lay.setConstraints(jb6, cons);
        add(jb6);
        
        cons.gridx = 0; cons.gridy = 2; 
        lay.setConstraints(jb7, cons);
        add(jb7);
        
        
        cons.gridx = 1; cons.gridy = 2; 
        cons.gridwidth = 2;
        lay.setConstraints(jb8, cons);
        add(jb8);
        
        cons.gridx = 3; cons.gridy = 2; 
        cons.gridwidth = 1;
        lay.setConstraints(jb9, cons);
        add(jb9);

Then I got this:

But I don't want this second row

Answer 1

Any suitable complex UI/layout should be split into multiple components. This is commonly known as "compound layouts".

This allows you to better focus on the individual needs of each "area" of the layout independently.

Sometimes, you just need to fake it.

Please note, I've used labels instead of button as a demonstration only, as MacOs buttons have a lot of space around them and this better illustrates the use of the GridBagConstraints#insets

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class Main {
    public static void main(String[] args) {
        new Main();
    }

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.weightx = 1;
            gbc.fill = gbc.HORIZONTAL;
            gbc.insets = new Insets(4, 0, 4, 0);
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            add(makeFirstRow(), gbc);
            add(makeSecondRow(), gbc);
            add(makeThirdRow(), gbc);
        }

        protected JLabel makeLabel(String text) {
            JLabel label = new JLabel(text);
            label.setHorizontalAlignment(JLabel.CENTER);
            label.setOpaque(true);
            label.setBackground(Color.RED);
            label.setBorder(new EmptyBorder(8, 32, 8, 32));
            return label;
        }

        protected JPanel makeFirstRow() {
            JPanel rowPane = new JPanel(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.weightx = 1;
            gbc.fill = gbc.HORIZONTAL;
            gbc.insets = new Insets(0, 4, 0, 4);

            rowPane.add(makeLabel("1"), gbc);
            rowPane.add(makeLabel("2"), gbc);

            return rowPane;
        }

        protected JPanel makeSecondRow() {
            JPanel rowPane = new JPanel(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.weightx = 1;
            gbc.fill = gbc.HORIZONTAL;
            gbc.insets = new Insets(0, 4, 0, 4);

            rowPane.add(makeLabel("3"), gbc);
            rowPane.add(makeLabel("4"), gbc);
            rowPane.add(makeLabel("5"), gbc);

            return rowPane;
        }

        protected JPanel makeThirdRow() {
            JPanel rowPane = new JPanel(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.weightx = 1;
            gbc.fill = gbc.HORIZONTAL;
            gbc.insets = new Insets(0, 4, 0, 4);

            rowPane.add(makeLabel("6"), gbc);
            rowPane.add(makeLabel("7"), gbc);
            rowPane.add(makeLabel("8"), gbc);

            return rowPane;
        }
    }

}

Now, I don't know about you, but I was tempted to create some kind of factory method which would create each row, based on the number of elements I needed in each row ... but that's me

but with a little bit different layout. button 4 (and 7 in your layout) should be same size as buttons 1 and 2, but in your case they are 2/3 of the size of 1 and 2, and buttons 3 and 5 should be 1/2 of 1 and 2, and here they are 2/3

Then change the columns weightx property accordingly, for example...

protected JPanel makeSecondRow() {
    JPanel rowPane = new JPanel(new GridBagLayout());
    GridBagConstraints gbc = new GridBagConstraints();
    gbc.fill = gbc.HORIZONTAL;
    gbc.insets = new Insets(0, 4, 0, 4);

    gbc.weightx = 0.25;
    rowPane.add(makeLabel("3"), gbc);
    gbc.weightx = 0.5;
    // This is simply adding an addition padding to the
    // labels preferred size, otherwise all three buttons
    // can be layed out at there preferred size with the
    // avaliable space
    gbc.ipadx = 64;
    rowPane.add(makeLabel("4"), gbc);
    gbc.weightx = 0.25;
    gbc.ipadx = 0;
    rowPane.add(makeLabel("5"), gbc);

    return rowPane;
}

Now, remember, the components own preferred size plays into this. Without the additional ipadx, all three elements can be layed out their preferred size with in the available container area.

And, no, you don't "need" to specify the weightx for each column, this is just a demonstration, but sometimes, you might find it more useful to be absolute in your desires.

Answer 2

I finally got this GUI to work, but I had to use two hacks that I don't recommend using.

Oracle has a helpful tutorial, Creating a GUI With Swing. Skip the Learning Swing with the NetBeans IDE section.

The reason this GUI is difficult to achieve is that the GridBagLayout has nothing to use to size the four columns. So, borrowing from the OP, I created a row of empty JLabels before creating the rows of JButtons. I sized the JLabels based on the size of a JButton.

I wasn't sure until I tried it, but a gridheight of zero keeps the JLabels in the same physical location as the first row of JButtons.

Here's the complete, ugly, runnable code.

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;

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

public class GridBagLayoutTest2 implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new GridBagLayoutTest2());
    }

    @Override
    public void run() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(createPanels(), BorderLayout.CENTER);

        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private JPanel createPanels() {
        JPanel panel = new JPanel(new GridBagLayout());

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.anchor = GridBagConstraints.LINE_START;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.insets = new Insets(5, 5, 5, 5);
        gbc.weightx = 0.0;
        
        JButton button1 = new JButton("Button 1");
        Dimension d = button1.getPreferredSize();
        
        gbc.gridheight = 0;
        gbc.gridwidth = 1;
        gbc.gridx = 0;
        gbc.gridy = 0;
        for (int index = 0; index < 4; index++) {
            JLabel label = new JLabel();
            label.setPreferredSize(d);
            panel.add(label, gbc);
            gbc.gridx++;
        }

        gbc.gridheight = 1;
        gbc.gridwidth = 2;
        gbc.gridx = 0;
        gbc.gridy++;
        gbc.weightx = 1.0;
        panel.add(button1, gbc);
        
        gbc.gridx += 2;
        JButton button2 = new JButton("Button 2");
        panel.add(button2, gbc);
        
        gbc.gridwidth = 1;
        gbc.gridx = 0;
        gbc.gridy++;
        JButton button3 = new JButton("Button 3");
        panel.add(button3, gbc);
        
        gbc.gridwidth = 2;
        gbc.gridx += 1;
        JButton button4 = new JButton("Button 4");
        panel.add(button4, gbc);
        
        gbc.gridwidth = 1;
        gbc.gridx += 2;
        JButton button5 = new JButton("Button 5");
        panel.add(button5, gbc);

        return panel;
    }

}

Answer 3

I would use one additional JPanel for each line, and would not extend JFrame (unless needed, that is, adding functionality to it)):

public class SwingApp2 {
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(SwingApp2::new);
    }

    private SwingApp2()
    {
        var jb1 = new JButton("1");
        var jb2 = new JButton("2");
        var jb3 = new JButton("3");
        var jb4 = new JButton("4");
        var jb5 = new JButton("5");

        var line1 = new JPanel(new GridBagLayout());
        var gbc = new GridBagConstraints(RELATIVE, 0, 1, 1, 1.0, 1.0, CENTER, BOTH, new Insets(0, 0, 0, 0), 0, 0);
        line1.add(jb1, gbc);
        line1.add(jb2, gbc);

        var line2 = new JPanel(new GridBagLayout());
        line2.add(jb3, gbc);
        gbc.weightx *= 2;
        line2.add(jb4, gbc);
        gbc.weightx /= 2;
        line2.add(jb5, gbc);

        var frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        // using GridLayout so the lines are same height
        frame.setLayout(new GridLayout(0, 1));
        frame.add(line1);
        frame.add(line2);
        frame.setSize(700,200);
        frame.setVisible(true);
    }
}

Result:

_{Just one way to do it, very dependent of how the components should be resized if the GUI size is changed
Also be aware that sizes will change according to preferred size, that is, labels content}

Answer 4

GridBagLayout is concerned with alignment, not proportions. Occasionally it can be used to lay out components with equal sizes, but it’s not good at that.

SpringLayout, however, is quite good at that, and has methods specifically for doing that. The trade-off is that SpringLayout is hard to use and easy to use incorrectly. It works like the “form layouts” of the 1990s. For each component in the layout, you have to state where at least one horizontal edge and one vertical edge should be located, relative to the edges of the container or relative to the edges of other child components.

First, it’s better to create your container, rather than extending JFrame. It doesn’t make sense to subclass JFrame, since you’re merely using JFrame, not changing its behavior:

SpringLayout layout = new SpringLayout();
JPanel panel = new JPanel(layout);

Next, let’s compute a consistent size for the small buttons:

JButton[] buttons = { jb1, jb2, jb3, jb4, jb5 };

Spring width = Spring.constant(0);
Spring height = Spring.constant(0);
for (JButton button : buttons) {
    width = Spring.max(width, Spring.width(button));
    height = Spring.max(height, Spring.height(button));
}

Next, let’s make buttons 1, 2, and 4 twice as wide:

Spring largeButtonWidth = Spring.scale(width, 2);

Now we can use those Springs to create constraints for each button:

Spring zero = Spring.constant(0);

panel.add(jb1, new SpringLayout.Constraints(
    zero, zero, largeButtonWidth, height));

panel.add(jb2, new SpringLayout.Constraints(
    largeButtonWidth, zero, largeButtonWidth, height));

panel.add(jb3, new SpringLayout.Constraints(
    zero, height, width, height));

panel.add(jb4, new SpringLayout.Constraints(
    width, height, largeButtonWidth, height));

panel.add(jb5, new SpringLayout.Constraints(
    Spring.sum(width, largeButtonWidth), height, width, height));

Finally, we need to tell the layout how big the container itself should be. It needs to be wide enough to accommodate jb2 and jb5, and tall enough to accommodate jb3, jb4, and jb5. We could use any of those to specify the container’s preferred size, but jb5 is probably the easiest choice:

layout.putConstraint(
    SpringLayout.EAST, panel, 0, SpringLayout.EAST, jb5);
layout.putConstraint(
    SpringLayout.SOUTH, panel, 0, SpringLayout.SOUTH, jb5);

Putting it all together looks like this:

import java.awt.EventQueue;

import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JFrame;
import javax.swing.Spring;
import javax.swing.SpringLayout;

public class RelativeButtonSizesDemo {
    private final JFrame frame;

    public RelativeButtonSizesDemo() {
        JButton jb1 = new JButton("1");
        JButton jb2 = new JButton("2");
        JButton jb3 = new JButton("3");
        JButton jb4 = new JButton("4");
        JButton jb5 = new JButton("5");

        JButton[] buttons = { jb1, jb2, jb3, jb4, jb5 };

        Spring width = Spring.constant(0);
        Spring height = Spring.constant(0);
        for (JButton button : buttons) {
            width = Spring.max(width, Spring.width(button));
            height = Spring.max(height, Spring.height(button));
        }

        // jb1, jb2, and jb4 will be twice as wide as the other buttons.
        Spring largeButtonWidth = Spring.scale(width, 2);

        SpringLayout layout = new SpringLayout();
        JPanel panel = new JPanel(layout);

        Spring zero = Spring.constant(0);

        panel.add(jb1, new SpringLayout.Constraints(
            zero, zero, largeButtonWidth, height));

        panel.add(jb2, new SpringLayout.Constraints(
            largeButtonWidth, zero, largeButtonWidth, height));

        panel.add(jb3, new SpringLayout.Constraints(
            zero, height, width, height));

        panel.add(jb4, new SpringLayout.Constraints(
            width, height, largeButtonWidth, height));

        panel.add(jb5, new SpringLayout.Constraints(
            Spring.sum(width, largeButtonWidth), height, width, height));

        // Set preferred size of panel itself to accommodate buttons.
        layout.putConstraint(
            SpringLayout.EAST, panel, 0, SpringLayout.EAST, jb5);
        layout.putConstraint(
            SpringLayout.SOUTH, panel, 0, SpringLayout.SOUTH, jb5);

        frame = new JFrame("Relative Button Sizes Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setLocationByPlatform(true);
    }

    public void show() {
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new RelativeButtonSizesDemo().show());
    }
}

Answer 5

The reason this GUI is difficult to achieve is that the GridBagLayout has nothing to use to size the four columns

GridBagLayout does have properties that allow you to define default values for columns that don't have components as is demonstrated below:

import java.util.*;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;

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

public class GridBagLayoutTest3 implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new GridBagLayoutTest3());
    }

    @Override
    public void run() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(createPanels(), BorderLayout.CENTER);

        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private JPanel createPanels() {

        //  Create the GridBagLayout and GridBagConstraints to be used by the panel

        GridBagLayout gbl = new GridBagLayout();
        JPanel panel = new JPanel(gbl);

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.anchor = GridBagConstraints.LINE_START;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.insets = new Insets(5, 5, 5, 5);

        //  Create and add components to the panel

        JButton button1 = new JButton("Button 1");
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 2;
        panel.add(button1, gbc);

        gbc.gridx += 2;
        JButton button2 = new JButton("Button 2");
        panel.add(button2, gbc);

        gbc.gridwidth = 1;
        gbc.gridx = 0;
        gbc.gridy++;
        JButton button3 = new JButton("Button 3");
        panel.add(button3, gbc);

        gbc.gridwidth = 2;
        gbc.gridx += 1;
        JButton button4 = new JButton("Button 4");
        panel.add(button4, gbc);

        gbc.gridwidth = 1;
        gbc.gridx += 2;
        JButton button5 = new JButton("Button 5");
        panel.add(button5, gbc);

        //  Set properties of the GridBagLayout for columns without components in a single column

        int[] columns = new int[4];
        Arrays.fill(columns, button1.getPreferredSize().width);
        gbl.columnWidths = columns;
        double[] weights = new double[4];
        Arrays.fill(weights, 1.0);
        gbl.columnWeights = weights;

        return panel;
    }

}

Note: you can also check out: https://stackoverflow.com/a/57463596/131872 which has a more involved example showing how to use this approach for a "keyboard" layout of buttons.