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Java component positioning on GridBagLayout

I am trying to position components on JPanel using GridBagLayout but the output I am getting is completely off from what I expect. Hope to get some clarity with brilliant-minded ppl in stackoverflow:).
Below I have provided a piece of code and screentshot of the program. My questions are:
Why the JLabel Choose measure system to convert is not on Y-axis = 1? As to my knowledge, c.gridy=1 is one pixel downward, but the label is stuck on the top leaving no space from the Frame title. And also, why is it positioned so weird, i.e., not really in the center, nor in the start?
Why is there such a big space between ComboBoxes From... and To..., but there is no space between ComboBox To... and TextField Enter value here...?
Here is the code:
JPanel container = new JPanel();
container.setLayout(new GridBagLayout());
getContentPane().add(container, BorderLayout.NORTH);
TitledBorder outputCenter;
GridBagConstraints c = new GridBagConstraints();
label = new JLabel("Choose measure system to convert");
label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
c.gridx = 0;
c.gridy = 1;
container.add(label, c);
fromList = new JComboBox<String>(convertFrom);
c.gridx = 0;
c.gridy = 2;
container.add(fromList, c);
toList = new JComboBox<String>(convertTo);
c.gridx = 1;
c.gridy = 2;
container.add(toList, c);
//Field where user enters the value to be converted
input = new JTextField("Enter value here...");
input.setPreferredSize(new Dimension(150,30));;
input.setEditable(true);
input.setBackground(Color.WHITE);
input.setBorder(BorderFactory.createLineBorder(Color.BLACK));
input.addMouseListener(new MouseAdapter(){
public void mouseClicked(MouseEvent e){
input.setText("");}});
c.gridx = 2;
c.gridy = 2;
container.add(input, c);
And here is the screentshot:
EDIT: If I change the code from:
label = new JLabel("Choose measure system to convert");
label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
c.gridx = 0;
c.gridy = 1;
container.add(label, c);
label = new JLabel("Choose measure system to convert");
label.setFont(new Font("Times New Roman", Font.PLAIN, 20));
c.gridx = 1; // changed this line
c.gridy = 1;
container.add(label, c);
The outcome is like this:
This is very confusing me as why changing the position of one component effects everything?

GridBagConstraints sets up the frame into effectively a grid. The width and height of the cells in the grid are determined by the size of the data in the cell by default unless otherwise specified. So if you want to add some space in-between cells I suggest ipadx and ipady. You can also utilize anchor for adjusting your data in the cell. I also suggest weightx and weighty for adjusting the actual cell size.
So imagine something like this as your current set up:
EDIT: Example of what your new GBC looks like. The numbers are (gridx,gridy)

Why the JLabel Choose measure system to convert is not on Y-axis = 1? As to my knowledge, c.gridy=1 is one pixel downward
You're confusing yourself, c.gridy = 1 is not positioning it 1 pixel downward but rather on the next row, but as there's no previous row, then it takes the first row. For reference see: GridBagConstraints#gridy which says the following:
Specifies the cell at the top of the component's display area, where the topmost cell has gridy=0. The value RELATIVE specifies that the component be placed just below the component that was added to the container just before this component was added.
Next question:
And also, why is it positioned so weird, i.e., not really in the center, nor in the start?
It is centered in its own cell, if you want to center it on the JFrame, then you might need to create it on its own gridx = 1 and the rest of components on the other ones (0 and 2) or make it span 2 or more columns based on you want it to look like...
Why is there such a big space between ComboBoxes From... and To..., but there is no space between ComboBox To... and TextField Enter value here...?
It is because your program is giving it all the extra space because of the large text on the first cell...
You can have something like this:
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class GridBagLayoutExample {
private JFrame frame;
private JPanel pane;
private JLabel label;
private JTextField field;
private JComboBox<String> box1;
private JComboBox<String> box2;
private GridBagConstraints gbc;
public static void main(String[] args) {
SwingUtilities.invokeLater(new GridBagLayoutExample()::createAndShowGui);
}
private void createAndShowGui() {
frame = new JFrame(getClass().getSimpleName());
pane = new JPanel();
pane.setLayout(new GridBagLayout());
gbc = new GridBagConstraints();
label = new JLabel("Choose measure system to convert");
box1 = new JComboBox<>(new String[] {"From..."});
box2 = new JComboBox<>(new String[] {"To..."});
field = new JTextField(10);
gbc.insets = new Insets(5, 5, 5, 5); //We add extra space at top, left, bottom, right of each component
gbc.gridx = 0;
gbc.gridy = 0;
gbc.gridwidth = 3; //We make our text to span 3 cells
pane.add(label, gbc);
gbc.gridy = 1;
gbc.gridwidth = 1; //We return the spanning to 1 single cell
pane.add(box1, gbc);
gbc.gridx = 1;
pane.add(box2, gbc);
gbc.gridx = 2;
pane.add(field, gbc);
frame.add(pane);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
Which produces the following output:

GridBagLayout creating very small panels

I am trying to set the layout of a JFrame to be a grid bag layout. I want to to essentially look like 4 grids of equal size, but with the bottom 2 merged into one panel. I am adding JPanels to each. However, I get 3 small grids at the middle of the JFrame, not properly sized. It looks like this instead.
My code is as follows:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Hangman extends JPanel{
private String word;
private JPanel hA, gL, letters;
public void setupLayout(JFrame window){
window.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
hA = new JPanel();
hA.setBackground(Color.blue);
c.fill = GridBagConstraints.BOTH;
c.gridx = 0;
c.gridy = 0;
window.add(hA, c);
gL = new JPanel();
gL.setBackground(Color.green);
c.fill = GridBagConstraints.BOTH;
c.gridx = 1;
c.gridy = 0;
window.add(gL, c);
letters = new JPanel();
letters.setBackground(Color.black);
c.fill = GridBagConstraints.BOTH;
c.weightx = 1.0;
c.gridx = 0;
c.gridy = 1;
c.gridwidth = 2;
window.add(letters, c);
}
public void startWindow(){
JFrame window = new JFrame();
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
int screenHeight = (int) screenSize.getHeight();
int windowHeight = (int) ((screenHeight / 4) * 3);
window.setSize(windowHeight, windowHeight);
window.setLocationRelativeTo(null);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setupLayout(window);
window.setVisible(true);
}
public void startGame(){
Prep prepare = new Prep();
word = prepare.findWord(true);
startWindow();
}
public static void main(String[] args){
Hangman start = new Hangman();
start.startGame();
}
}
It's not very important what Prep does. It just takes a random word from a text file. I couldn't see how it would affect the layout. To recap, I need to make it so each of the 4 grid spaces span one fourth of the window, and then make the bottom 2 cells merged with a JPanel added to each of them. Any help is appreciated. Thank you in advance.
EDIT:
I needed to set the weight of all of them to be 1. It is solved.

GridBagLayout displays each component at its preferred size. Since you didn't add any components to the panels you just see a small panel.
If you want the panels to fill the space available then you need to play with the constraints.
Read the section from the Swing tutorial on How to Use GridBagLayout for more information and working examples. You will want to look at the "fill" and "weightx/weighty" constraints.
and then make the bottom 2 cells merged
you will also need to look at the "gridwidth/gridheight" constraints.

Setting GridBagLayout grid's size

I'm trying to create a console using Java Swing (GridBagLayout).
I don't know why, but as you can see at the left margin, grids don't have the correct size.
It's supposed to be shown this way:
Where light blue is the list, green the image, orange the text panel and yellow the text field.
I don't know how to make the list bigger and the image smaller. Too, the text field's grid is binded to the list one, even tough the list is on y 1 and the text field on y 2.
Here's some code.
// Command List
DefaultListModel<String> listInput = new DefaultListModel<String>();
JList<String> list = new JList<String>(listInput);
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
JScrollPane scrollPane = new JScrollPane(list);
list.setBackground(new Color(160, 160, 160));
list.setSelectionBackground(new Color(150, 150, 150));
scrollPane.setPreferredSize(new Dimension(20, 20));
manager.setCommandList(listInput);
c.insets = new Insets(2, 2, 2, 2);
c.ipady = 0;
c.ipadx = 100;
c.gridx = 0;
c.gridy = 1;
c.gridwidth = 1;
c.gridheight = 2;
c.weightx = 0.1;
c.weighty = 0.6;
c.fill = GridBagConstraints.BOTH;
console.add(scrollPane, c);
// Image Displayer
JLabel image = new JLabel(new ImageIcon());
manager.setImageField(image);
c.insets = new Insets(0, 0, 0, 0);
c.ipady = 0;
c.ipadx = 0;
c.gridx = 0;
c.gridy = 0;
c.gridwidth = 1;
c.gridheight = 1;
c.weightx = 0.1;
c.weighty = 0.3;
c.fill = GridBagConstraints.BOTH;
console.add(image, c);
where 'c' is a grid bag constraint and console the main JPanel.
As you can see, the list has a grid height of 2 and weight of 0.6, and the image a grid height of 1 and weight of 0.9, so not sure why the list is 4 times smaller than the image.
Another issue, I've added a listener to the JLabel holding the image (on resize), anyways, it isn't called. Should I add the listener to the main panel? as the image is only being resized by the layout manager.
Thanks ^^
EDIT:
SSCCE:
package co.relieved.jelly.application.display.swing;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.Insets;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.DefaultListModel;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTabbedPane;
import javax.swing.JTextField;
import javax.swing.JTextPane;
import javax.swing.ListSelectionModel;
#SuppressWarnings("serial")
public class Test extends JPanel {
static JLabel image;
public static void main(String[] args) {
display();
try {
BufferedImage buffer = ImageIO
.read(new File("/home/juanco/Pictures/Screenshot from 2016-02-08 22-43-22.png"));
image.setIcon(new ImageIcon(
buffer.getScaledInstance(image.getWidth(), image.getHeight(), BufferedImage.SCALE_SMOOTH)));
} catch (IOException ex) {
ex.printStackTrace();
}
}
public Test() {
super(new GridLayout(1, 1));
JTabbedPane tabs = new JTabbedPane();
/*** >>> Console Pane <<< ***/
JPanel console = new JPanel();
console.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.ipadx = 0;
c.ipady = 0;
c.gridwidth = 1;
c.anchor = GridBagConstraints.CENTER;
c.fill = GridBagConstraints.BOTH;
// Console Screen
JTextPane screen = new JTextPane();
screen.setEditable(false);
c.gridx = 1;
c.gridy = 0;
c.gridheight = 2;
c.weightx = 0.8;
c.weighty = 1;
console.add(screen, c);
// Console Input
JTextField input = new JTextField();
c.insets = new Insets(2, 0, 2, 0);
c.ipady = 3;
c.gridy = 2;
c.gridheight = 1;
c.weighty = 0;
c.fill = GridBagConstraints.HORIZONTAL;
console.add(input, c);
// Command List
DefaultListModel<String> listInput = new DefaultListModel<String>();
listInput.setSize(1);
JList<String> list = new JList<String>(listInput);
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
JScrollPane scrollPane = new JScrollPane(list);
c.insets = new Insets(2, 2, 2, 2);
c.ipady = 0;
c.ipadx = 100;
c.gridx = 0;
c.gridy = 1;
c.gridheight = 2;
c.weightx = 0.1;
c.weighty = 0.6;
c.fill = GridBagConstraints.BOTH;
console.add(scrollPane, c);
// Image Displayer
image = new JLabel(new ImageIcon());
c.insets = new Insets(0, 0, 0, 0);
c.ipadx = 0;
c.gridy = 0;
c.gridheight = 1;
c.weighty = 0.3;
console.add(image, c);
// General
tabs.addTab("Console", console);
/*** >>> Logs Pane <<< ***/
JPanel logs = new JPanel();
tabs.addTab("Logs", logs);
// Setup
tabs.setSelectedIndex(0);
add(tabs);
}
static void display() {
JFrame frame = new JFrame("Relieved Console");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setPreferredSize(new Dimension(800, 500));
frame.add(new Test(), BorderLayout.CENTER);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}

Here's some code.
Which doesn't help. The grid can only be completed with the entire code. That is we need to know the gridwidth and gridheight for all components in order to determine the allocation of space to each component in the grid.
the text field's grid is binded to the list one, even tough the list is on y 1 and the text field on y 2.
You can't just randomly assign a component to a grid. The component will only go to grid 2 if the component above it has a grid height of 2. So basically each of your columns needs to have components with a total grid height of 3.
I don't know how to make the list bigger
Setting a preferred size of (20, 20) doesn't help. Anyway you should not be using the setPreferredSize() method.
Instead you should be using:
list.setVisibleRowCount(...);
to specify the visible rows. Then the JList can determine its own preferred size.
Another layout option is to use nested panels which can simplify the layout.
So you could start with a "west" panel that uses a BorderLayout. Then you add the label to "PAGE_START" and the list to "CENTER".
Then you create a "center" panel. Add the main component to the "CENTER" and the text field to the "PAGE_START".
Then you add the two panels to the frame:
frame.add(westPanel, BorderLayout.LINE_START);
frame.add(centerPanel, BorderLayout.CENTER);
Edit:
Sorry, I take back my comment about making each column have a grid height of 3. You can't just specify a total grid height of 3 because you only have 2 components in each column, so each component can only have a height of 1.
Check out my answer in this posting: Why does this GridBagLayout not appear as planned? for a hack that allows you to manipulate gridHeight/Weight by using invisible components in a row/column.
However, I don't recommend that approach. it will be far easier to use my suggestion of nested panels using a BorderLayout (or some other layout manager on the nested panels).

It seems to me that you would need to also specify the gridwidth and/or gridheight for the text field as well.
GridBagLayout is like a glorified GridLayout. It will attempt to align all of the components with the nearest grid spaces around it. Oracle's Tutorials also describe this behavior.
Much of the time, issues with laying out components using GridBagLayout come from the other components being added to the layout instead of the apparent problem child.

I fixed it splitting the "console" JPanel in two, a border layout panel to the left and a grid bag layout panel to the right. As #camickr suggested

Java : gridbaglayout confusion

this is my first question on here, so please forgive me when i am breaking any rules, or not using the right format
I am creating a simple form in java swing which consists of 1 JLabel, 1 JTextField, and 1 Button
|---------------------------|
| |
| JLabel |
| |
|---------------------------|
| JTextField | Button |
|---------------------------|
The Button should be in the bottom-right corner, the JTextField left of it, the JLabel on the top, spanning both columns
I want the Button to be a fixed size, the JTextField a fixed height, but using the full width (except for what is in use by the Button), and the JLabel using all other space (with and height)
I am not even sure if i should use a GridBagLayout or another Layout ?
This is probably a very easy question, but got me puzzled for quite some time (too many options with the GridBarLayout i guess)

First, set the layout of your panel to GridBagLayout.
Then, create a GridBagConstraints object and set the fill to GridBagConstraints.BOTH.
For the JLabel, set the following properties on the constraints object: gridx = 0, gridy = 0, gridwidth = 2, gridheight = 2, weightx = 1, weighty = 1.
For the JTextField, set the following properties on the constraints object: gridx = 0, gridy = 1, gridwidth = 1, gridheight = 1, weightx = 1, weighty = 0.
For the JButton, set the following properties on the constraints object: gridx = 1, gridy = 1, gridwidth = 1, gridheight = 1, weightx = 0, weighty = 0.

Class BorderLayout is easy to use, less powerful than GridBagLayout.
But when thing are simple, solution have to be the same.
panel.add( label, BorderLayout.CENTER );
JPanel south = new JPanel();
south.add( textfield );
south.add( button );
button.setPreferredSize( x, y );
panel.add( south, BorderLayout.SOUTH );

OK here is a demo code that should get you going:
import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class TestGridBagLayout {
protected void initUI() {
JFrame frame = new JFrame(TestGridBagLayout.class.getSimpleName());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton button = new JButton("A button");
JTextField textField = new JTextField();
JLabel label = new JLabel("A cool long nice label that will stretch.");
label.setHorizontalAlignment(JLabel.CENTER);
label.setBorder(BorderFactory.createLineBorder(Color.GREEN));
JPanel panel = new JPanel(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.fill = GridBagConstraints.BOTH;// Fill the "cell" in both direction
gbc.weightx = 1.0;// Allocate extra-width to the label
gbc.weighty = 1.0;// Allocate extra-height to the label
gbc.gridwidth = GridBagConstraints.REMAINDER;// The label takes all the available width of the "row"
panel.add(label, gbc);
gbc.weighty = 0; // Don't stretch TF vertically
gbc.fill = GridBagConstraints.HORIZONTAL; // Fill horizontally
gbc.gridwidth = GridBagConstraints.RELATIVE;
panel.add(textField, gbc);
gbc.weightx = 0; // No extra horizontal space is given to the button
gbc.fill = GridBagConstraints.NONE; // No fill for the button
panel.add(button, gbc);
frame.add(panel);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TestGridBagLayout().initUI();
}
});
}
}

I don't know this is a common thing to do, but below is code which is working (mainly code from Dan and Guillaume)
//show stuff
setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
//show label
c.fill = GridBagConstraints.BOTH; // Fill the "cell" in both direction
c.weightx = 1.0; // Allocate extra-width to the label
c.weighty = 1.0; // Allocate extra-height to the label
c.gridwidth = GridBagConstraints.REMAINDER; // The label takes all the available width of the "row"
add(mlblShow,c);
//show cmd txt
c.weighty = 0; // Don't stretch TF vertically
c.fill = GridBagConstraints.BOTH; // Fill horizontally and vertically
c.gridwidth = GridBagConstraints.RELATIVE;
add(mtxtCmd,c);
//show send button
c.weightx = 0; // No extra horizontal space is given to the button
c.fill = GridBagConstraints.NONE; // No fill for the button
add(cmdSend,c);

Java-Swing: A problem using layout managers!

I'm working on a JDialog (by hand, no GUI builders) and I'm having a problem doing the layout.
I have this:
My problem is that I don't know what how to tell that JList (within a JScrollPane) to have a Maximum width, I used the setSize, setMaximumSize and nothing works! I need that JList's width to be the half of the picture's size.
Explain the layouts:
The "Gene Information" is a GridLayout 2x4, it's contained by a JPanel with BoxLayout, the +/- JButtons is a BoxLayout also, all what I said before is within a BoxLayout.
Now, the "Genes" JPanel is a GridBagLayout.
What can I do?
Thanks in advance!
PD: The other borders are just for seeign the boundaries of the components.
Source Code:
scpGenesList.setViewportView(lstGenesList);
pnlGeneInfo.setLayout(new GridLayout(4, 2, 10, 10));
pnlGeneInfo.setBorder(BorderFactory.createCompoundBorder(
BorderFactory.createTitledBorder("Gene Information"),
BorderFactory.createEmptyBorder(10, 10, 10, 10)));
lblGeneSymbol.setText("Symbol:");
lblGeneSymbol.setHorizontalAlignment(SwingConstants.RIGHT);
lblGeneChromosome.setText("Chromosome:");
lblGeneChromosome.setHorizontalAlignment(SwingConstants.RIGHT);
lblGeneStartPosition.setText("Start Position:");
lblGeneStartPosition.setHorizontalAlignment(SwingConstants.RIGHT);
lblGeneStopPosition.setText("Stop Position:");
lblGeneStopPosition.setHorizontalAlignment(SwingConstants.RIGHT);
pnlGeneInfo.add(lblGeneSymbol);
pnlGeneInfo.add(lblGeneSymbolValue);
pnlGeneInfo.add(lblGeneChromosome);
pnlGeneInfo.add(lblGeneChromosomeValue);
pnlGeneInfo.add(lblGeneStartPosition);
pnlGeneInfo.add(lblGeneStartPositionValue);
pnlGeneInfo.add(lblGeneStopPosition);
pnlGeneInfo.add(lblGeneStopPositionValue);
pnlGWASAddRemoveButtons.setLayout(new BoxLayout(pnlGWASAddRemoveButtons, BoxLayout.X_AXIS));
pnlGWASAddRemoveButtons.add(Box.createHorizontalGlue());
pnlGWASAddRemoveButtons.add(cmdGenesAdd);
pnlGWASAddRemoveButtons.add(Box.createHorizontalStrut(10));
pnlGWASAddRemoveButtons.add(cmdGenesRemove);
pnlGWASAddRemoveButtons.add(Box.createHorizontalGlue());
pnlGeneInfoButtons.setLayout(new BoxLayout(pnlGeneInfoButtons, BoxLayout.Y_AXIS));
pnlGeneInfoButtons.add(pnlGeneInfo);
pnlGeneInfoButtons.add(Box.createVerticalStrut(10));
pnlGeneInfoButtons.add(pnlGWASAddRemoveButtons);
pnlGenesPanel.setLayout(new GridBagLayout());
pnlGenesPanel.setBorder(BorderFactory.createCompoundBorder(
BorderFactory.createTitledBorder("Genes"),
BorderFactory.createEmptyBorder(10, 10, 10, 10)));
GridBagConstraints ctrGenes = new GridBagConstraints();
ctrGenes.fill = GridBagConstraints.BOTH;
ctrGenes.gridx = 0;
ctrGenes.gridy = 0;
ctrGenes.gridwidth = 1;
ctrGenes.gridheight = 1;
ctrGenes.weighty = 1.0;
ctrGenes.weightx = 1.0;
ctrGenes.insets = new Insets(0, 0, 0, 10);
pnlGenesPanel.add(scpGenesList, ctrGenes);
GridBagConstraints ctrGenesInfoButton = new GridBagConstraints();
ctrGenesInfoButton.fill = GridBagConstraints.BOTH;
ctrGenesInfoButton.gridx = 1;
ctrGenesInfoButton.gridy = 0;
ctrGenesInfoButton.gridwidth = 1;
ctrGenesInfoButton.gridheight = 1;
ctrGenesInfoButton.weighty = 1.0;
ctrGenesInfoButton.weightx = 1.0;
pnlGenesPanel.add(pnlGeneInfoButtons, ctrGenesInfoButton);
contentPane.add(pnlGenesPanel);
pack();

Why not give the "Genes" panel a 2x1 GridLayout? That should ensure that both sides have the same size.
But actually, it would make more sense to me to give the list all space not taken by the controls, since those require a fixed amount of space while the list may benefit from all additional space it can get, if there are wide entries.
To that end, I would give the "Genes" panel a BorderLayout, put the list in the CENTER slot and the controls in the EAST slot.

Following #Michael Borgwardt's suggestion to let the list grow, you can use setVisibleRowCount() to produce a convenient initial panel size. If necessary, you can also examine the Dimension returned by getPreferredScrollableViewportSize(), which "computes the size of viewport needed to display visibleRowCount rows."

Without seeing all the code here it may be impossible to tell you what is wrong. One thing I would suggest if you have time is to take a look at MigLayout. You can use it with Swing & SWT and once you learn it is a pretty powerful layout manager IMHO.
Hope this helps, good luck.

It doesn't answer your question - but I've found that the JGoodies FormLayout to be more intuitive than the GridBagLayout. The library, as well as some examples, can be found here:
http://jgoodies.com/freeware/forms/index.html

I think the earlier solutions are all valid, and it is more of a coding preference in terms of which layout managers to use. Based on your requirement, here is a working one with standard layout managers only (Grid, GridBag and Border). Have fun, - MS.
import java.awt.;
import javax.swing.;
import javax.swing.border.*;
public class GeneDialog extends JDialog {
private String[] plusMinus = {"+","-"}, tfNames = {
"Symbol", "Chromosome", "Start position", "Stop position"},
listData = {"Gene01", "Gene02", "Gene03", "Gene04", "Gene05", "Gene06",
"Gene07", "Gene08", "Gene09", "Gene10", "Gene11", "Gene12"};
private JTextField[] gtField= new JTextField[tfNames.length];
private JList list = new JList (new DefaultListModel());
public GeneDialog (Frame f, String title) {
super (f, title, true);
Container cp = getContentPane();
cp.setLayout (new GridLayout(1,2));
JScrollPane listScrollPane = new JScrollPane (list);
listScrollPane.setBorder(BorderFactory.createCompoundBorder(
BorderFactory.createTitledBorder("Genes"),
BorderFactory.createEmptyBorder(10, 10, 10, 10)));
DefaultListModel lm = (DefaultListModel) list.getModel();
for (int k = 0 ; k < listData.length ; k++)
lm.addElement (listData[k]);
cp.add (listScrollPane);
cp.add (controlPanel());
pack();
}
private GridBagConstraints makeGBC (int inset) {
GridBagConstraints gbc = new GridBagConstraints();
gbc.insets = new Insets (inset, inset, inset, inset);
gbc.fill = GridBagConstraints.HORIZONTAL;
gbc.gridx = 0;
gbc.gridy = GridBagConstraints.RELATIVE;
return gbc;
}
private JPanel controlPanel() {
JPanel cp = new JPanel (new BorderLayout()),
bp = new JPanel (new GridBagLayout()),
tp = new JPanel (new GridBagLayout());
GridBagConstraints gbc = makeGBC (10);
for (int i = 0 ; i < tfNames.length ; i++) {
JLabel label = new JLabel (tfNames[i], JLabel.TRAILING);
tp.add (label, gbc);
}
gbc.gridx++; gbc.weightx = 1.0f;
for (int i = 0 ; i < tfNames.length ; i++) {
gtField[i] = new JTextField(12);
tp.add (gtField[i], gbc);
}
gbc = makeGBC (10);
for (int i = 0 ; i < plusMinus.length ; i++) {
JButton b = new JButton (plusMinus[i]);
bp.add (b, gbc);
gbc.gridx++;
}
cp.add (tp, "Center");
cp.add (bp, "South");
return cp;
}
public static void main (String[] args) {
new GeneDialog (null, "Genes").setVisible (true);
}}

Try setting the maximum width for both the JScrollPane and the JList that is within it.

I just want to tell that I share the same opinion as javamonkey79. Take a look at MigLayout, you'll love it, and from Java 7 on it will be standart java-onboard layout.