Java Swing GridBagLayout - adding buttons without space

Question

How can I remove spacing caused by gridBagLayout and make them stick together?
Here is my code simply adding 3 buttons. I read this question but there was no complete solution How to fix gap in GridBagLayout;
I just want to put all of my buttons on the top of the JFrame.

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

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

public class MyProblem {

    private JFrame frame = new JFrame();

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

    public MyProblem() {
        frame.setLayout(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();
        gc.weightx = 1;
        gc.weighty = 1;
        gc.gridx = 0;
        gc.gridy = 0;
        gc.fill = GridBagConstraints.HORIZONTAL;
        gc.anchor = GridBagConstraints.NORTH;
        for (int i = 0; i < 3; i++) {
            JPanel jPanel = new JPanel(new BorderLayout());
            jPanel.setSize(80, 80);
            jPanel.add(new JButton("Button " + i),BorderLayout.PAGE_START);
            frame.add(jPanel, gc);
            gc.gridy++;
        }

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 500);
        frame.setVisible(true);
    }

}

How my buttons look like:

How I want my buttons to look like:

Answer 1

This code will do the job:

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;

public class MyProblem {

    private JFrame frame = new JFrame();

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

    public MyProblem() {
        frame.setLayout(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();
        gc.weightx = 1;
        gc.weighty = 0;
        gc.gridx = 0;
        gc.gridy = 0;
        gc.ipadx = 0;
        gc.ipady = 0;
        gc.fill = GridBagConstraints.HORIZONTAL;
        gc.anchor = GridBagConstraints.NORTH;
        for (int i = 0; i < 3; i++) {
            JButton button = new JButton("Button " + i);
            frame.add(button, gc);
            gc.gridy++;
        }
        gc.weighty = 1;
        frame.add(Box.createGlue(), gc); //Adding a component to feel the area.
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 500);
        frame.setVisible(true);
    }

}

Answer 2

The layout makes a single column of buttons, so..

Change:

        gc.fill = GridBagConstraints.HORIZONTAL;

To:

        gc.fill = GridBagConstraints.BOTH;

Edit 1

I want to keep buttons to the same height as described in picture and just putting them at the top.

To constrain them to the top is fairly easy using a combined layout. In this case we might add the panel with the buttons into the PAGE_START of a panel with BorderLayout. That part of a border layout will stretch the width of the child component (our panel with GridLayout) to fill the available space, but it will respect the height of whatever is in it - giving the component only as much vertical space as it needs.

Edit 2

Here is an MCVE that implements the idea described above. The outer panel (with a cyan colored border) is used to constrain the height of the button panel (with orange border). See the comments in the source for more detail on how it works.

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

public class MyProblem {

    private JFrame frame = new JFrame();

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

    public MyProblem() {
        frame.setLayout(new BorderLayout()); // actually the default

        // we will use this panel to constrain the panel with buttons
        JPanel ui = new JPanel(new BorderLayout());
        frame.add(ui);
        ui.setBorder(new LineBorder(Color.CYAN, 3));

        // the panel (with GridLayout) for the buttons
        JPanel toolPanel = new JPanel(new GridLayout(0,1,0,4)); // added some gap
        toolPanel.setBorder(new LineBorder(Color.ORANGE, 3));
        // toolPanel will appear at the top of the ui panel
        ui.add(toolPanel, BorderLayout.PAGE_START); 
        for (int i = 0; i < 3; i++) {
            toolPanel.add(new JButton("Button " + i));
        }

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //frame.setSize(500, 500); // instead..
        frame.pack(); // pack will make it as small as it can be.
        frame.setMinimumSize(frame.getSize()); // nice tweak..
        frame.setVisible(true);
    }
}

Answer 3

Run this code I think you will get help from it

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

public class Think {

public static void addComponentsToPane(Container pane) {

    JButton jbnButton;
    pane.setLayout(new GridBagLayout());
    GridBagConstraints gBC = new GridBagConstraints();
    gBC.fill = GridBagConstraints.HORIZONTAL;

    jbnButton = new JButton("Button 1");
    gBC.weightx = 0.5;
    gBC.gridx = 0;
    gBC.gridy = 0;
    pane.add(jbnButton, gBC);

    jbnButton = new JButton("Button 3");
    gBC.gridx = 2;
    gBC.gridy = 0;
    pane.add(jbnButton, gBC);

    jbnButton = new JButton("Button 4");
    gBC.ipady = 40;     //This component has more breadth compared to other buttons
    gBC.weightx = 0.0;
    gBC.gridwidth = 3;
    gBC.gridx = 0;
    gBC.gridy = 1;
    pane.add(jbnButton, gBC);

}

private static void createAndShowGUI() {

    JFrame.setDefaultLookAndFeelDecorated(true);
    JFrame frame = new JFrame("GridBagLayout Source Demo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Set up the content pane.
    addComponentsToPane(frame.getContentPane());

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

public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
    });
 }
}