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Box Layout Won't Align Left

I have a custom panel (APanel). Two questions:
I need the label ("Top Label") and sub panel (bPanel) to align on the left side of the panel. bPanel is aligning on the left side but Top Label is being place in the middle. How do I fix?
How do I set the label and bPanel so they don't change in vertical size and maintain the same vertical distance between each other when the entire frame is expanded? In other words, how do I prevent the below from happening?
Code for APanel and bPanel are below. In case it matters, APanel is loaded as the CENTER component in a JFrame set to BorderLayout (not including the frame code here).
public class APanel extends JPanel {
private JLabel jLabel1;
private BPanel bPanel;
public APanel () {
this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
jLabel1 = new JLabel("Top Label", JLabel.LEFT);
jLabel1.setHorizontalAlignment(SwingConstants.LEFT);
jLabel1.setBorder(BorderFactory.createLineBorder(Color.BLACK));
add(jLabel1);
bPanel = new BPanel();
bPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
add(bPanel);
this.setAlignmentX(LEFT_ALIGNMENT);
}
private class bPanel extends JPanel {
private JLabel sLabel;
private JLabel tLabel;
public bPanel() {
sLabel = new JLabel("Jeepers");
tLabel = new JLabel("Creepers");
setLayout(new GridBagLayout());
GridBagConstraints gc = new GridBagConstraints();
gc.gridx = 0;
gc.gridy = 0;
gc.weightx = 1;
gc.weighty = 1;
gc.fill = GridBagConstraints.HORIZONTAL;
add(sLabel, gc);
gc.gridx = 1;
add(tLabel, gc);
}
}
}

I need the label ("Top Label") and sub panel (bPanel) to align on the left side of the panel.
jLabel1.setHorizontalAlignment(SwingConstants.LEFT);
Wrong method to control alignment with respect to the container. Read the JLabel API. That method is used to align the text within the bounds of the JLabel, in case the size of the label is greater than the preferred size of the text.
this.setAlignmentX(LEFT_ALIGNMENT);
Close, but that is not needed because if refers to the alignment of this entire panel in its parent container.
Instead, you need to set the "alignment" of all the components you are adding the this panel using the vertical BoxLayout. Each component may have a different default value. Some will default to "left" and some to "center".
Read the section from the Swing tutorial on Fixing Alignment Problems for more information.
How do I set the label and bPanel so they don't change in vertical size and maintain the same vertical distance between each other when the entire frame is expanded?
The BoxLayout will allow components to grow (up to their maximum size) when extra space is available. For a JLabel the maximum size is the same as its preferred size. For a JPanel the maximum size is the value of Integer.MAX_VALUE.
So you can override the getMaximumSize() method of you panel with code something like:
#Override
public Dimension getMaximumSize()
{
Dimension preferred = getPreferredSize();
Dimension maximum = super.getMaximumSize();
maximum.height = preferred.height;
return maximum;
}
Or another option is to wrap the panel in another panel that will respect the height. For example.
JPanel wrapper = new JPanel( new BorderLayout() );
wrapper.add(bPanel, BorderLayout.PAGE_START);
add(wrapper);
//add(bPanel);

Please suggest me a basic layout to use, other than the GridBag layout

OK I have a panel, and I want to place two panels on to it, left and right, such that the right panel should be double the width of the left side panel.
I want to add a menu to the left side panel, and the details of the selected item will appear in the right side panel.
Secondly, the size of the panels and their components should increase proportionately when the window is expanded (If any methods can be used for the purpose, please suggest!)
I did try to use the GridBagLayout but I think I have not yet been able to grasp it well. So please suggest the simplest layout manager which can serve my purpose.
EDIT:- PROBLEMS WITH WHAT I HAD TRIED WITH THE GRIDBAG
//Set Layout
setLayout(new GridBagLayout());
GridBagConstraints c= new GridBagConstraints();
//Set Layout constraints of components and add them to the MainPanel
c.gridx=0;
c.gridy=0;
c.weightx=0.5;
c.insets= new Insets(5,5,5,5);
c.fill=GridBagConstraints.BOTH;
add(iListPanel);
iListPanel.setBorder(BorderFactory.createTitledBorder("Check") );
GridBagConstraints c1= new GridBagConstraints();
c.gridx=1;
c.gridy=0;
c.weightx=1;
c.insets= new Insets(5,5,5,5);
c.fill=GridBagConstraints.BOTH;
add(iDetailsPanel);
iDetailsPanel.setBorder(BorderFactory.createTitledBorder("Check"));

Of the layout managers that come with Java, I think GridBagLayout is the simplest one that will do that. It's worth the time to learn it, because it's about the only layout manager that's halfway-competent. This should do it:
JPanel panel = new JPanel();
panel.setLayout(new GridBagLayout());
GridBagConstraints c;
JPanel left = new JPanel();
left.setBorder(BorderFactory.createTitledBorder("Left"));
c = new GridBagConstraints();
c.weightx = 1;
c.weighty = 1;
c.fill = c.BOTH;
panel.add(left, c);
JPanel right = new JPanel();
right.setBorder(BorderFactory.createTitledBorder("Right"));
c = new GridBagConstraints();
c.weightx = 2;
c.weighty = 1;
c.fill = c.BOTH;
panel.add(right, c);
However, from the description of your problem, it sounds like JSplitPane will serve you better for this. It's a ready-made component to do more-or-less what you're asking, and has a user-resizeable separator as well. An example:
JSplitPane pane = new JSplitPane();
pane.setResizeWeight(1/3f); // right will be twice size of left
JPanel left = new JPanel();
left.setBorder(BorderFactory.createTitledBorder("Left"));
pane.setLeftComponent(left);
JPanel right = new JPanel();
right.setBorder(BorderFactory.createTitledBorder("Right"));
pane.setRightComponent(right);
Edit: The problem with your original code is that it does not use the constraints.
add(iListPanel);
should be:
add(iListPanel, c);
and likewise for iDetailsPanel.

You want to use a BorderLayout.
panel.add(panelLeft,"West");
panel.add(panelRight,"East");
North, South and Center is also available

GridBagLayout panel expands ignoring BoxLayout's vertical glue

In the example below I have a JPanel with BoxLayout which contains another JPanel with GridBagLayout.
By adding a vertical glue I expect the contents of the inner panel to be "glued" to the top of the outer panel.
But I see the label "A" in the center. If I remove GridBagLayout, A is shown at the top.
Why does this happen?
import javax.swing.*;
import java.awt.*;
public class Test {
public static void main(String[] args) {
JPanel contentPane = new JPanel();
JFrame frame = new JFrame();
frame.setContentPane(contentPane);
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
JPanel gridBagPanel = new JPanel();
gridBagPanel.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.fill = GridBagConstraints.NONE;
gridBagPanel.add(new JLabel("A"), gbc);
contentPane.add(gridBagPanel);
contentPane.add(Box.createVerticalGlue());
frame.setSize(800, 200);
frame.setVisible(true);
}
}

Because the default value of the anchor property of GridBagConstraints is CENTER. If there is more space in the inner panel than the preferred size of the JLabel, the JLabel would be centered with respect to the available space in the inner panel (since you set fill to NONE).
You can use the anchor value NORTHWEST to glue the label to the top of the panel:
GridBagConstraints gbc = new GridBagConstraints();
gbc.fill = GridBagConstraints.NONE;
gbc.anchor = GridBagConstraints.NORTHWEST;
gbc.weighty = 1;
gbc.weightx = 1;
You also need to set the weights per Java documentation: "Unless you specify at least one non-zero value for weightx or weighty, all the components clump together in the center of their container. This is because when the weight is 0.0 (the default), the GridBagLayout puts any extra space between its grid of cells and the edges of the container."

It's probably because GridBagLayout is a pain in the butt and you should consider using other layout managers. Or it could be that you need to set the horizontal and vertical alignment of your components. Take a look at setAlignmentX and setAlignmentY of JComponent. Whenever I've had misbehaved components it's because I didn't align everything the same.

Although Kavka s' Answer solves the requirement of having A on the top of the panel by using an anchor, I believe the declared vertical glue in the BoxLayout Panel doesn't actually do anything. So, I am going to expand on this to contribute what I figured out about using the weights and the vertical glue in GridBagLayouts.
Since GridBagLayout is a complex one, there may be more than one reason, but as Kavka already pointed out:
the weightx and weighty modification from default value 0.0 to a non-zero value is the key.
As pointed out in the Java Tutorial Documentation on GridBagConstraints , in the description section of the JavaDoc for GridBagLayout and the specific parameter description in the JavaDoc for GridBagConstraints.
If all the weights are zero, all the extra space appears between the grids of the cell and
for weightx the extra space appears additionally between the left and right edges.
for weighty the extra space appears additionally between the top and bottom edges.
So, if you wanted to use some vertical glue to fill empty cells you need to make sure you give a non-zero weight to the glue component in the direction you would like it to expand. I am going to solely use the GridBagLayout, so the gridy parameter is going to allow me to define the vertical distribution of the components.
Taking the original code as example base and extending it a bit to demonstrate the capabilities of vertical glue in combination with weights. This code will position A at 20% from the top of the panel, maintaining this ratio when resized:
import javax.swing.*;
import java.awt.*;
public class Test {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel gridBagPanel = new JPanel();
gridBagPanel.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridy = 0;
gbc.weighty = 0.2;
gridBagPanel.add(Box.createVerticalGlue(), gbc);
gbc.gridy = 1;
gbc.weighty = 0;
gridBagPanel.add(new JLabel("A"), gbc);
gbc.gridy = 2;
gbc.weighty = 0.8;
gridBagPanel.add(Box.createVerticalGlue(), gbc);
frame.setContentPane(gridBagPanel);
frame.setSize(800, 200);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
For specifics on how the glue works see Java Tutorial on How to Use BoxLayout, Filler section

Starting GridBagLayout from top left corner in Java Swing

I'm new to Java Swing and I have been struggling to start the GridBagLayout from top left corner so that c.gridx=0 c.gridy=0 will put my object on the top left corner.
I'd appreciate if you could help me by telling what I need to do after this point:
JPanel panel = new JPanel(new GridBagLayout());
frame.add(panel);
GridBagConstraints c = new GridBagConstraints();
I know that I have to use NORTHWEST or FIRST_LINE_START constants, but I don't know how. I tried to do it this way' but it did not realize the constants.
frame.getContentPane().add(panel, BorderLayout.NORTHWEST);
Thanks for your help.

Read the section from the Swing tutorial on How to Use GridBagLayout. The secton on "weightx,weighty" states:
Unless you specify at least one non-zero value for weightx or weighty, all the components clump together in the center of their container.

You need to use your GridBagConstraints' anchor property. This should do it for you:
frame.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.anchor = GridBagConstraints.NORTHWEST;
frame.add(panel, gbc);
I'm not guaranteeing that you won't have to set other properties of the constraints object to get the layout you desire. In particular, you may need to set weightx and weighty to be 1 so that the panel takes up all of the available space given to it.

For those, who use IDE (e.g. NetBeans), I finally found nice trick: if you want to add components to top and use their preferred sizes: add another empty panel with weighty = 1.0. Copied from auto-generated code (NetBeans):
gridBagConstraints = new java.awt.GridBagConstraints();
gridBagConstraints.gridx = 0;
gridBagConstraints.gridy = 2;
gridBagConstraints.weighty = 1.0;
jPanelOptions.add(jPanelFiller, gridBagConstraints);

a quick and simple way:
add a blank JLabel to end of page:
// your code goes here
gbc.weightx = 1;
gbc.weighty = 1;
bg.add(new JLabel(" "), gbc); // blank JLabel

There's a workaround. You can put the GridBagLayout panel in a BorderLayout panel with BorderLayout.NORTH. Then Component in GridBagLayout panel will start from top position.
static void test4(){
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(480, 360);
JPanel borderLayoutPanel=new JPanel(new BorderLayout());
JPanel gridBagLayoutPanel = new JPanel(new GridBagLayout());
borderLayoutPanel.add(gridBagLayoutPanel, BorderLayout.NORTH);
frame.add(borderLayoutPanel);
JButton testButton=new JButton("test button");
GridBagConstraints c = new GridBagConstraints();
c.gridx=0;
c.gridy=0;
gridBagLayoutPanel.add(testButton, c);
frame.setVisible(true);
}

if you want the grid to go all the way to the top, simply set all your weighty = 0 until the last item, set it to any number greater than 0, it will effectively push the rest of the buttons to the top.
Don't forget to also increment your button's gridy value.
Otherwise it will be centered.
(the same can be done using gridx and weightx value if you arent using the c.fill = GridBagConstraints.HORIZONTAL property.)

How to set the component size with GridLayout? Is there a better way?

I am working on a larger GUI with Java and I am becoming angry on Layout Managers.
I have a "Settings-Panel" with a variable number of JComponents in it (Labels, Buttons, JSpinners, JSliders,...). I just want the following:
JLabel <-> JComponent
JLabel <-> JComponent
JLabel <-> JComponent
...
My Panel has a size of 500px, so that there is enough space for a lot of components. Unfortunately the GridLayout always stretches the size of the Components to the whole Panel, even if I set a MaximumSize for every component. It looks stupid if there are only two buttons each with a height of 250px.
I tried FlowLayout, but I cannot figure out a way to make new lines properly. I tried BoxLayout.Y_AXIS, but the Components are always centered, and Label and Component are not in the same line.
Does anybody know a good and short way with LayoutManagers to handle this properly?

An alternative to other layouts, might be to put your panel with the GridLayout, inside another panel that is a FlowLayout. That way your spacing will be intact but will not expand across the entire available space.

Don't use GridLayout for something it wasn't meant to do. It sounds to me like GridBagLayout would be a better fit for you, either that or MigLayout (though you'll have to download that first since it's not part of standard Java). Either that or combine layout managers such as BoxLayout for the lines and GridLayout to hold all the rows.
For example, using GridBagLayout:
import java.awt.*;
import javax.swing.*;
public class LayoutEg1 extends JPanel{
private static final int ROWS = 10;
public LayoutEg1() {
setLayout(new GridBagLayout());
for (int i = 0; i < ROWS; i++) {
GridBagConstraints gbc = makeGbc(0, i);
JLabel label = new JLabel("Row Label " + (i + 1));
add(label, gbc);
JPanel panel = new JPanel();
panel.add(new JCheckBox("check box"));
panel.add(new JTextField(10));
panel.add(new JButton("Button"));
panel.setBorder(BorderFactory.createEtchedBorder());
gbc = makeGbc(1, i);
add(panel, gbc);
}
}
private GridBagConstraints makeGbc(int x, int y) {
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = 1;
gbc.gridheight = 1;
gbc.gridx = x;
gbc.gridy = y;
gbc.weightx = x;
gbc.weighty = 1.0;
gbc.insets = new Insets(5, 5, 5, 5);
gbc.anchor = (x == 0) ? GridBagConstraints.LINE_START : GridBagConstraints.LINE_END;
gbc.fill = GridBagConstraints.HORIZONTAL;
return gbc;
}
private static void createAndShowUI() {
JFrame frame = new JFrame("Layout Eg1");
frame.getContentPane().add(new LayoutEg1());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}

For more complex layouts I often used GridBagLayout, which is more complex, but that's the price. Today, I would probably check out MiGLayout.

In my project I managed to use GridLayout and results are very stable, with no flickering and with a perfectly working vertical scrollbar.
First I created a JPanel for the settings; in my case it is a grid with a row for each parameter and two columns: left column is for labels and right column is for components. I believe your case is similar.
JPanel yourSettingsPanel = new JPanel();
yourSettingsPanel.setLayout(new GridLayout(numberOfParams, 2));
I then populate this panel by iterating on my parameters and alternating between adding a JLabel and adding a component.
for (int i = 0; i < numberOfParams; ++i) {
yourSettingsPanel.add(labels[i]);
yourSettingsPanel.add(components[i]);
}
To prevent yourSettingsPanel from extending to the entire container I first wrap it in the north region of a dummy panel, that I called northOnlyPanel.
JPanel northOnlyPanel = new JPanel();
northOnlyPanel.setLayout(new BorderLayout());
northOnlyPanel.add(yourSettingsPanel, BorderLayout.NORTH);
Finally I wrap the northOnlyPanel in a JScrollPane, which should behave nicely pretty much anywhere.
JScrollPane scroll = new JScrollPane(northOnlyPanel,
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
Most likely you want to display this JScrollPane extended inside a JFrame; you can add it to a BorderLayout JFrame, in the CENTER region:
window.add(scroll, BorderLayout.CENTER);
In my case I put it on the left column of a GridLayout(1, 2) panel, and I use the right column to display contextual help for each parameter.
JTextArea help = new JTextArea();
help.setLineWrap(true);
help.setWrapStyleWord(true);
help.setEditable(false);
JPanel split = new JPanel();
split.setLayout(new GridLayout(1, 2));
split.add(scroll);
split.add(help);

You need to try one of the following:
GridBagLayout
MigLayout
SpringLayout
They offer many more features and will be easier to get what you are looking for.

I used WrapFlowLayout instead
JPanel yourPanel = new JPanel(new WrapFlowLayout(10, 10);