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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:

Issue when using Java Swing in a For-Loop

I have created a simple for-loop that changes the amount of JTextFields and JLabels based on the value of a JSpinner, as seen in the following code:
public static ArrayList<ArrayList<JTextField>> ChangeQuestionAnswerFields(int numberOfQuestions){
ArrayList<ArrayList<JTextField>> txtFieldArray = new ArrayList<ArrayList<JTextField>>();
JPanel scrollPanel = new JPanel(new GridBagLayout());
//JScrollPane scrollPane = new JScrollPane(scrollPanel);
frame.add(scrollPanel, BorderLayout.CENTER);
GridBagConstraints c = new GridBagConstraints();
c.gridx = 0;
c.gridy = 0;
for(int i = 0; i != numberOfQuestions; i++){
JTextField tempQuestion = new JTextField(10);
JTextField tempAnswer = new JTextField(10);
JLabel tempQuestionHeader = new JLabel("Question " + (i + 1)+ " ");
JLabel tempQuestionLbl = new JLabel("Question: ");
JLabel tempAnswerLbl = new JLabel("Answer: ");
ArrayList<JTextField> tempArrayList = new ArrayList<>();
tempArrayList.add(tempQuestion);
tempArrayList.add(tempAnswer);
txtFieldArray.add(tempArrayList);
c.gridy++;
c.gridx = 0;
scrollPanel.add(tempQuestionHeader, c);
c.gridy++;
c.gridx = 0;
scrollPanel.add(tempQuestionLbl, c);
c.gridx = 1;
c.gridwidth = 3;
scrollPanel.add(tempQuestion, c);
c.gridy++;
c.gridx = 0;
scrollPanel.add(tempAnswerLbl, c);
c.gridx = 1;
c.gridwidth = 3;
scrollPanel.add(tempAnswer, c);
}
return txtFieldArray;
}
}
The value of the Spinner is passed into the method, and the method is called using a change listener (where noQuestions is the value of the JSpinner):
noQuestions.addChangeListener(e -> {
ChangeQuestionAnswerFields((int) noQuestions.getValue());
frame.revalidate();
frame.repaint();
});
This method is first called in the code when the screen first appears, and works properly. However, whenever the value of the spinner changes the original labels and fields stay on the screen and more text fields simply appear, or disappear on top.
http://i.imgur.com/GBY8L3u.png - JSpinner has a value of 2
http://i.imgur.com/pSQsA3G.png - JSpinner has a value of 3
Is there any way to fix this? Any help is much appreciated.
Thanks,
Tom
Minimal Runnable Example:
import javax.swing.*;
import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
public class MainGUI {
static JFrame frame = new JFrame("Math Reviser");
public static void main(String[] args) {
frame.setSize(400, 600);
frame.setVisible(true);
createScreen();
frame.revalidate();
frame.repaint();
public static void createScreen(){
frame.getContentPane().removeAll();
JSpinner noQuestions = new JSpinner(new SpinnerNumberModel(1, 1, 10, 1));
frame.add(noQuestions, BorderLayout.NORTH);
);
changeQuestionAnswerFields(1);
frame.revalidate();
frame.repaint();
noQuestions.addChangeListener(e -> {
changeQuestionAnswerFields((int) noQuestions.getValue());
frame.revalidate();
frame.repaint();
});
}
public static ArrayList<ArrayList<JTextField>> changeQuestionAnswerFields(int numberOfQuestions){
ArrayList<ArrayList<JTextField>> txtFieldArray = new ArrayList<ArrayList<JTextField>>();
JPanel scrollPanel = new JPanel(new GridBagLayout());
frame.add(scrollPanel, BorderLayout.CENTER);
GridBagConstraints c = new GridBagConstraints();
c.gridx = 0;
c.gridy = 0;
for(int i = 0; i != numberOfQuestions; i++){
JTextField tempQuestion = new JTextField(10);
JTextField tempAnswer = new JTextField(10);
JLabel tempQuestionHeader = new JLabel("Question " + (i + 1)+ " ");
JLabel tempQuestionLbl = new JLabel("Question: ");
JLabel tempAnswerLbl = new JLabel("Answer: ");
ArrayList<JTextField> tempArrayList = new ArrayList<>();
tempArrayList.add(tempQuestion);
tempArrayList.add(tempAnswer);
txtFieldArray.add(tempArrayList);
c.gridy++;
c.gridx = 0;
scrollPanel.add(tempQuestionHeader, c);
c.gridy++;
c.gridx = 0;
scrollPanel.add(tempQuestionLbl, c);
c.gridx = 1;
c.gridwidth = 3;
scrollPanel.add(tempQuestion, c);
c.gridy++;
c.gridx = 0;
scrollPanel.add(tempAnswerLbl, c);
c.gridx = 1;
c.gridwidth = 3;
scrollPanel.add(tempAnswer, c);
}
return txtFieldArray;
}
}

Using static variables and methods is an indication of a poorly designed application. There is no need for the static variables or methods. I suggest you read the section from the Swing tutorial on How to Use Labels. The LabelDemo.java code will show you how to create a panel containing all the components. This panel will then be added to the frame. This panel will also contain all the instance variables you need for your program.
Not only that the example will show you how to create the GUI components on the EDT which is something you should always do to prevent random errors since Swing was designed to be single threaded.
However, the main problem with your existing code is that you continue to create and add new panels to the content pane of the frame. Try changing the spinner to 2 and then resize the frame. Then try changing the spinner to 3 and resize the frame. After the resizing the first panel is displayed. This is because Swing will paint the last component added first so the first panel added will be painted on top of the last panel you created.
You can change this in your existing code by removing the old panel before adding the new panel:
static JFrame frame = new JFrame("Math Reviser");
static JPanel scrollPanel = new JPanel();
...
frame.remove(scrollPanel);
//JPanel scrollPanel = new JPanel(new GridBagLayout());
scrollPanel = new JPanel(new GridBagLayout());
However, I do not recommend this approach. As I initially suggestion you need to redesign the entire class. When you do the redesign I would use a BorderLayout on your panel and then you can add your spinner to the PAGE_START and then add a JScrollPane to the CENTER of the panel.
Then when you want to create a new panel you add the panel to the scrollpane using code like:
scrollPane.setViewportView( scrollPanel );
The scrollpane will refresh itself and you don't need to worry about revalidate() or repaint() or anything else.

TextBox not displaying on frame until the frame is stretched manually

I am trying to create a login page. I wrote code for two textboxes and one button. One textbox next to Username and other one next to Password. One "Sign In" button below. But I am not sure why the textbox's and button are not shown on my output. I only get the Username and password label's on my ouput screen.
Strange thing is whenever I stretch my output frame, (I mean either pulling the screen horizontally or vertically) the two textboxes and the button shows up.
Please check my code and let me know what's wrong. I was trying to put pictures to make easier to understand but I do not have enough reputation. Please help.
import javax.swing.*;
import java.awt.*;
public class HomeScreen{
public static void main(String args[]){
JFrame frame = new JFrame("Medical Store");
frame.setVisible(true);
frame.setSize(600,400);
JPanel panel = new JPanel(new GridBagLayout());
frame.getContentPane().add(panel, BorderLayout.NORTH);
GridBagConstraints c = new GridBagConstraints();
JLabel label1 = new JLabel("Username");
c.gridx = 0;
c.gridy = 0;
c.insets = new Insets(10,10,10,10);
panel.add(label1,c);
JLabel label2 = new JLabel("Password");
c.gridx = 0;
c.gridy = 1;
panel.add(label2,c);
JTextField textbox1 = new JTextField(10);
c.gridx = 1;
c.gridy = 1;
panel.add(textbox1,c);
JTextField textbox2 = new JTextField(10);
c.gridx = 2;
c.gridy = 1;
panel.add(textbox2,c);
JButton button1 = new JButton("Sign In");
c.gridx = 1;
c.gridy = 2;
panel.add(button1,c);
}
}

You're calling setVisible(true) before adding all components, and so your GUI is doing just that, drawing itself before components are added.
JFrame frame = new JFrame("Medical Store");
frame.setVisible(true);
// all components added here
Solution: make the setVisible(true) call at the end after adding all components.
JFrame frame = new JFrame("Medical Store");
// all components added here
frame.setVisible(true);
Now all components should be visualized.
Other quibbles:
Avoid calling setSize(...) on anything. Instead let the layout managers and component preferred sizes do that for you.
Call pack() on the JFrame just prior to setting it visible so that the above will happen.

GridBagLayout - Height of one row causes the width of next row to change

The UI I am working on displays a panel which lets a user select a movie and play. There are controls to play, pause, etc.
The layout seems to look the way I want. The panel uses a GridBagLayout. Row 2 displays a text area for status messages and row 3 displays a panel with buttons and a progress bar.
The problem I am running into is that when I have too many lines of text in the text area, the buttons in row 3 wrap around. This is irrespective of the height of the outer frame.
The height in row 2 is affecting the width in row 3. I don't understand this behavior. I am wondering if someone can tell me what is it that I am doing wrong and how I can fix it? I have attached the code.
On a slightly different topic, if you are looking at the code, can you also suggest a way to leave a margin between the bottom-most component and the outermost panel?
Thank you in advance for your help.
Regards,
Peter
private static JButton CreateImageButton(String fileName) {
JButton retVal = new JButton("xxx");
return retVal;
}
public MoviePanel() {
this.setLayout(new GridBagLayout());
this.setBackground(Color.WHITE);
JButton btnRefresh = CreateImageButton("refresh.png");
GridBagConstraints c = new GridBagConstraints();
c.gridx=0;
c.gridy=0;
c.fill = GridBagConstraints.NORTH;
c.insets.left = 10; c.insets.right = 10; c.insets.top = 10;
this.add(btnRefresh, c);
JComboBox cbMovieList = new JComboBox();
c = new GridBagConstraints();
c.gridx = 1;
c.gridy = 0;
c.fill = GridBagConstraints.HORIZONTAL;
c.insets.right = 10; c.insets.top = 10;
c.weightx = 1.0;
this.add(cbMovieList, c);
JButton btnAuthorize = new JButton("Get Info");
c = new GridBagConstraints();
c.gridx = 1;
c.gridy = 1;
c.anchor = GridBagConstraints.WEST;
c.insets.top = 10;
this.add(btnAuthorize, c);
JTextArea txtInfo = new JTextArea();
txtInfo.setFont( new Font("SansSerif", Font.BOLD, 12));
txtInfo.setBackground(Color.cyan);
// txtInfo.setText("abc\ndef");
txtInfo.setText("abc\ndef\nghi\njkl\nmno\npqr\nstu\nvwx\nyz");
c = new GridBagConstraints();
c.gridx = 1;
c.gridy = 2;
c.anchor = GridBagConstraints.NORTHWEST;
c.weighty = 1.0;
c.insets.top = 10;
this.add(txtInfo, c);
JPanel controllerOuter = new JPanel();
controllerOuter.setLayout(new BoxLayout(controllerOuter, BoxLayout.Y_AXIS));
controllerOuter.setBorder(BorderFactory.createRaisedBevelBorder());
FlowLayout controllerLayout = new FlowLayout(FlowLayout.CENTER);
controllerLayout.setHgap(0);
JPanel controller = new JPanel(controllerLayout);
controller.setBorder(new EmptyBorder(10, 10, 10, 10));
Dimension dim = new Dimension(60, 40);
JButton btnPlay = CreateImageButton("play.png");
btnPlay.setPreferredSize(dim);
controller.add(btnPlay);
JButton btnPause = CreateImageButton("pause.png");
btnPause.setPreferredSize(dim);
controller.add(btnPause);
JButton btnStop = CreateImageButton("stop.png");
btnStop.setPreferredSize(dim);
controller.add(btnStop);
JButton btnForward = CreateImageButton("forward.png");
btnForward.setPreferredSize(dim);
controller.add(btnForward);
JComboBox cbAspectRatio = new JComboBox();
cbAspectRatio.setPreferredSize(new Dimension(100, 40));
cbAspectRatio.setBorder(new EmptyBorder(0, 10, 0, 0));
controller.add(cbAspectRatio);
controllerOuter.add(controller);
JProgressBar pbProgress = new JProgressBar(0, 100);
pbProgress.setPreferredSize(new Dimension(350, 40));
pbProgress.setBorder(new EmptyBorder(0, 10, 10, 10));
pbProgress.setValue(50);
pbProgress.setString("50/100");
pbProgress.setStringPainted(true);
pbProgress.setForeground(Color.BLUE);
pbProgress.setBorderPainted(true);
controllerOuter.add(pbProgress);
c = new GridBagConstraints();
c.gridx = 0;
c.gridy = 3;
c.gridwidth = 2;
c.weightx = 1.0;
this.add(controllerOuter, c);
}

I see several things in your code:
You force the preferredSize of the JButton's. If possible, I would remove that because this will often get you more problems than solutions. If you want to force the preferredSize, you should also pay attention to set the minimum and maximum sizes as well, otherwise you get weird behaviour like the one you are observing
You use a BoxLayout to display the controls. While this is perfectly acceptable, BoxLayout also relies on min/max size to perform the layout, which you did not set.
You use imbricated layouts. This is fine too, but why not use only the GridBagLayout of your MoviePanel?
Usually TextAreas are wrapped in JScrollPane, in case the text is too big. You can also setLineWrap(true) on the TextArea, so that it does not go too far on the right. By setting rows/columns on the TextArea, you will define its preferreSize (to prevent it from depending of the text it contains).
On your GridBagConstraints, the fill property can only be: NONE, VERTICAL, HORIZONTAL or BOTH (You used VERTICAL for one of them). Also, it is not needed to recreate a new instance, you can reuse the same GridBagConstraint over and over, it is automatically cloned by the LayoutManager when you set the constraint for the component.
Now for the solutions, I found several:
When you add the contollerOuter, also specify c.fill = GridBagConstraints.HORIZONTAL; (This is the easiest way to solve your issues)
When you set the preferredSize of the JButtons, also force their minimumSize to the same value.
Use only the GridBagLayout to layout all components. (This would be my favorite)
Replace the FlowLayout by a BoxLayout with a X_AXIS.
Rember that GridBagConstraints properties :
gridx, gridy: specifies the location
gridwidth, gridheight: specifies the colspan/rowspan
weightx, weighty: specifies who gets the extra horizontal/vertical space and in what proportion
anchor: specifies the alignement of the component withing its "cell", if the "cell" is bigger than the component
fill: specifies if the component should stretch to the cell width/height

Just adding one JPanel each for Center and Bottom will do the trick for you, so till your JTextArea your GridBagLayout will server the purpose and after that the BorderLayout of the MAIN JPanel will do. Moreover, adding JScrollPane also to the whole thing reduces the effort needed at other areas. Have a look at the code and output :
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class JTextPaneExample extends JPanel
{
private Icon info = UIManager.getIcon("OptionPane.informationIcon");
private Icon error = UIManager.getIcon("OptionPane.errorIcon");
private static JButton CreateImageButton(String fileName) {
JButton retVal = new JButton("xxx");
return retVal;
}
private void createAndDisplayGUI()
{
JFrame frame = new JFrame("JTextPane Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setLayout(new BorderLayout());
this.setBackground(Color.WHITE);
JPanel centerPanel = new JPanel();
centerPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
centerPanel.setLayout(new GridBagLayout());
centerPanel.setBackground(Color.WHITE);
JButton btnRefresh = CreateImageButton("refresh.png");
GridBagConstraints c = new GridBagConstraints();
c.gridx=0;
c.gridy=0;
c.fill = GridBagConstraints.NORTH;
c.insets.left = 10; c.insets.right = 10; c.insets.top = 10;
centerPanel.add(btnRefresh, c);
JComboBox cbMovieList = new JComboBox();
c = new GridBagConstraints();
c.gridx = 1;
c.gridy = 0;
c.fill = GridBagConstraints.HORIZONTAL;
c.insets.right = 10; c.insets.top = 10;
c.weightx = 1.0;
centerPanel.add(cbMovieList, c);
JButton btnAuthorize = new JButton("Get Info");
c = new GridBagConstraints();
c.gridx = 1;
c.gridy = 1;
c.anchor = GridBagConstraints.WEST;
c.insets.top = 10;
centerPanel.add(btnAuthorize, c);
JTextArea txtInfo = new JTextArea();
txtInfo.setFont( new Font("SansSerif", Font.BOLD, 12));
txtInfo.setBackground(Color.cyan);
// txtInfo.setText("abc\ndef");
txtInfo.setText("abc\ndef\nghi\njkl\nmno\npqr\nstu\nvwx\nyz");
JScrollPane scroller = new JScrollPane();
scroller.setViewportView(txtInfo);
c = new GridBagConstraints();
c.gridx = 1;
c.gridy = 2;
c.anchor = GridBagConstraints.NORTHWEST;
c.fill = GridBagConstraints.HORIZONTAL;
c.weighty = 1.0;
c.insets.top = 10;
centerPanel.add(scroller, c);
JPanel controllerOuter = new JPanel();
controllerOuter.setLayout(new BoxLayout(controllerOuter, BoxLayout.Y_AXIS));
controllerOuter.setBorder(BorderFactory.createRaisedBevelBorder());
FlowLayout controllerLayout = new FlowLayout(FlowLayout.CENTER);
controllerLayout.setHgap(0);
JPanel controller = new JPanel(controllerLayout);
controller.setBorder(new EmptyBorder(10, 10, 10, 10));
Dimension dim = new Dimension(60, 40);
JButton btnPlay = CreateImageButton("play.png");
btnPlay.setPreferredSize(dim);
controller.add(btnPlay);
JButton btnPause = CreateImageButton("pause.png");
btnPause.setPreferredSize(dim);
controller.add(btnPause);
JButton btnStop = CreateImageButton("stop.png");
btnStop.setPreferredSize(dim);
controller.add(btnStop);
JButton btnForward = CreateImageButton("forward.png");
btnForward.setPreferredSize(dim);
controller.add(btnForward);
JComboBox cbAspectRatio = new JComboBox();
cbAspectRatio.setPreferredSize(new Dimension(100, 40));
cbAspectRatio.setBorder(new EmptyBorder(0, 10, 0, 0));
controller.add(cbAspectRatio);
controllerOuter.add(controller);
JProgressBar pbProgress = new JProgressBar(0, 100);
pbProgress.setPreferredSize(new Dimension(350, 40));
pbProgress.setBorder(new EmptyBorder(0, 10, 10, 10));
pbProgress.setValue(50);
pbProgress.setString("50/100");
pbProgress.setStringPainted(true);
pbProgress.setForeground(Color.BLUE);
pbProgress.setBorderPainted(true);
controllerOuter.add(pbProgress);
add(centerPanel, BorderLayout.CENTER);
add(controllerOuter, BorderLayout.PAGE_END);
frame.getContentPane().add(this);
frame.pack();
frame.setVisible(true);
}
public static void main(String... args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new JTextPaneExample().createAndDisplayGUI();
}
});
}
}
Here is the output as you add more lines :

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.