How to align vertically buttons of different sizes within a GridBagLayout?

Question

I'm starting with swing, I have some questions about how to align elements within a GridBagLayout, I'm not sure either whether this is the correct approach, please advice.

I have the below code

import javax.swing.*;
import java.awt.*;

public class App {
    public void start() {
        JPanel mainPanel = new JPanel(new FlowLayout());
        mainPanel.setBorder(BorderFactory.createLineBorder(Color.CYAN, 20));

        //buttons for initial options
        JButton button1 = new JButton("This is option A");
        JButton button2 = new JButton("option B");
        JButton button3 = new JButton("Another text");

        JPanel second = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.anchor = GridBagConstraints.CENTER;
        second.setBackground(Color.GREEN);
        second.add(button1, gbc);
        second.add(button2, gbc);
        second.add(button3, gbc);

        mainPanel.add(second, BorderLayout.CENTER);

        //frame configuration
        JFrame frame = new JFrame();
        frame.setContentPane(mainPanel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 600);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setResizable(false);
    }

    public static void main(String[] args) throws Exception {
        UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
        SwingUtilities.invokeLater(() -> new App().start());
    }
}

My goal is to produce the following output:

So far I have tried with BoxLayout with vertical alignment and it works but the problem is that it overwrites the preferred sized of the buttons and I want them all to be the same width.

Also, I tried with GridLayout and BorderLayout adding the elements to NORTH, CENTER, and SOUTH but the sizes of the buttons change.

What is the recommended way to center the elements but keeping their dimensions?

Answer 1

I would nest layouts:

1. A JPanel that holds the buttons and uses a new GridLayout(0, 1, 0, vGap) -- a grid that holds one column and variable number of rows, with a vGap gap between buttons.
2. Add that JPanel into another JPanel that uses GridBagLayout, and add it in a default way (no GridBagConstraints) which will center the first JPanel into the second. This would obviously have to somehow be the size desired. This can be achieved by either

• overriding getPreferredSize() in a sensible way
• Calling setPreferredSize(new Dimension(someWidth, someHeight)) -- this isn't quite as "clean"
• Giving this a border, specifically a BorderFactor.EmptyBorder(gap, gap, gap, gap) where gap is the size of the border around the JPanel...

Done.

Test code that uses the GridBagLayout:

import java.awt.Dimension;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import javax.swing.*;

public class ButtonLayout extends JPanel {
    public static final int MY_WIDTH = 750;
    public static final int MY_HEIGHT = 500;
    private static final float BTN_SIZE = 24f;
    
    private String[] buttonTexts = {"This is Option A", "Option B", 
            "Something Else Entirely"};
    
    public ButtonLayout() {
        int colGap = 20;
        JPanel buttonPanel = new JPanel(new GridLayout(0, 1, 0, colGap));
        for (String btnText : buttonTexts) {
            JButton button = new JButton(btnText);
            
            // set first letter of text as mnemonic (alt-char shortcut)
            int mnemonic = (int) btnText.charAt(0);
            button.setMnemonic(mnemonic);
            
            // make button bigger by increasing its font
            button.setFont(button.getFont().deriveFont(BTN_SIZE));
            
            // add to the GridLayout-using JPanel
            buttonPanel.add(button);
        }
        
        // set layout of main panel to GridBag
        setLayout(new GridBagLayout());
        
        // add the button panel in a "default" manner (no constraints)
        // which centers this panel
        add(buttonPanel);
    }
    
    @Override
    public Dimension getPreferredSize() {
        Dimension superSize = super.getPreferredSize();
        int width = Math.max(MY_WIDTH, superSize.width);
        int height = Math.max(MY_HEIGHT, superSize.height);
        
        return new Dimension(width, height);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

    private static void createAndShowGui() {
        ButtonLayout mainPanel = new ButtonLayout();
        JFrame frame = new JFrame("ButtonLayout");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

Example 2 that uses EmptyBorder:

import java.awt.GridLayout;
import javax.swing.*;

@SuppressWarnings("serial")
public class ButtonLayout extends JPanel {
    public static final int MY_WIDTH = 750;
    public static final int MY_HEIGHT = 500;
    private static final float BTN_SIZE = 24f;
    
    private String[] buttonTexts = {"This is Option A", "Option B", 
            "Something Else Entirely"};
    
    public ButtonLayout() {
        int colGap = 20;
        JPanel buttonPanel = new JPanel(new GridLayout(0, 1, 0, colGap));
        for (String btnText : buttonTexts) {
            JButton button = new JButton(btnText);
            
            // set first letter of text as mnemonic (alt-char shortcut)
            int mnemonic = (int) btnText.charAt(0);
            button.setMnemonic(mnemonic);
            
            // make button bigger by increasing its font
            button.setFont(button.getFont().deriveFont(BTN_SIZE));
            
            // add to the GridLayout-using JPanel
            buttonPanel.add(button);
        }
        
        add(buttonPanel);
        
        int top = 60;
        int left = top;
        int bottom = 2 * top;
        int right = left;
        setBorder(BorderFactory.createEmptyBorder(top, left, bottom, right));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

    private static void createAndShowGui() {
        ButtonLayout mainPanel = new ButtonLayout();
        JFrame frame = new JFrame("ButtonLayout");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}