Develop Reference

GridLayout doesn't fill up the entire window

Whats the reason that a JInteralFrame with a GridLayout(x, y) doesn't fill up the entire window although I'm adding x*y buttons to it? Why is there white space around it like in the first picture below?
If i resize it a bit, I'm able to remove all the white space around the grid layout, like in the second picture below, but I do not understand why that's not always the case.

Why is there white space around it like in the first picture below?
A GridLayout assigns exactly the same width or height to every component, but for a GUI 20 (for example) components wide, it is only possible to do that every 20 pixels that the GUI is stretched. It arranges any 'left over' pixels of space to the left and right most components.
To get around that, you might instead use a GridBagLayout and adjust the weights of rows and columns to allow some components to take over the remaining space in a way that is almost unnoticeable (the difference in component sizes) to the user.

Why is there white space around it like in the first picture below?
Andrew's answer explains the problem with the GridLayout.
However I don't know if this can be fixed with any of the other standard JDK layout managers.
Check out the Relative Layout. It is a layout manager that allows you to give components a size relative to one another, so it is easy to make all components the same size. When there are extra pixels you can set the "rounding policy" to allocate the pixels to different components.
The layout is a little more complex because it can't be done with a single layout manager. In the example below you need a panel that uses the RelativeLayout for vertical layout. Then you need to create a separate panel for each row and those panels will use a RelativeLayout with a horizontal layout.
import java.awt.*;
import javax.swing.*;
public class SSCCE extends JPanel
{
SSCCE()
{
int size = 10;
setBackground( Color.RED );
Float constraint = new Float(1.0f);
RelativeLayout vertical = new RelativeLayout(RelativeLayout.Y_AXIS);
vertical.setRoundingPolicy( RelativeLayout.EQUAL );
vertical.setFill(true);
setLayout( vertical );
for (int i = 0; i < size; i++)
{
RelativeLayout horizontal = new RelativeLayout(RelativeLayout.X_AXIS);
horizontal.setRoundingPolicy( RelativeLayout.EQUAL );
horizontal.setFill(true);
JPanel row = new JPanel( horizontal );
for (int j = 0; j < size; j++)
{
row.add(new JButton(), constraint);
}
add(row, constraint);
}
}
private static void createAndShowGUI()
{
JFrame frame = new JFrame("SSCCE");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new SSCCE());
frame.pack();
frame.setLocationByPlatform( true );
frame.setVisible( true );
}
public static void main(String[] args) throws Exception
{
EventQueue.invokeLater( () -> createAndShowGUI() );
/*
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowGUI();
}
});
*/
}
}

How do I limit the width of components of a JScrollPane

I have a JScrollPane with a number of JLabel objects in a panel using a GridBagLayout. Each of the labels is displaying HTML text with rich elements which varies at run time.
I would like all labels to have the same width (driven by the width of the scroll pane) but vary in height depending on their content with the text wrapping (as is handled automatically by JLabel). If the labels exceed the scroll pane's height then a vertical scroll bar should appear.
Here is some sample code to demonstrate the problem:
public class ScrollLabels extends JFrame {
private final JPanel labelPanel = new JPanel(new GridBagLayout());
private final GridBagConstraints c = new GridBagConstraints();
public ScrollLabels() throws HeadlessException {
super("Scroll Labels");
}
public void createUI() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JScrollPane scroller = new JScrollPane(labelPanel);
add(scroller);
c.gridx = 0;
c.gridy = GridBagConstraints.RELATIVE;
c.fill = GridBagConstraints.HORIZONTAL;
addLabel("Here is <em>Rich Text</em>");
addLabel("Here is <ul><li>A</li><li>List</li></ul>");
addLabel("Here is <table><tr><th>A</th><th>Table></th></tr></table");
addLabel("Here is more <em>Rich Text</em>");
addLabel("Here is even more <b>Rich Text</b>");
addLabel("Here is a long sentence that should wrap when the panel "
+ "is too small for the text.");
pack();
}
private void addLabel(String text) {
JLabel label = new JLabel("<html>" + text + "</html>");
label.setBorder(BorderFactory.createEtchedBorder());
labelPanel.add(label, c);
}
public static void main(String[] args) {
ScrollLabels frame = new ScrollLabels();
frame.createUI();
frame.setVisible(true);
}
}
It correctly resizes the labels horizontally and shows scroll bars where appropriate. What it doesn't do is resize labels vertically to fit them within the scroll pane.
Here are the various things I have tried:
Changing the GridBagConstraint values. There are good controls for how to expand and contract components but I can't see any way to set a min or max width.
Setting the JScrollPane scroll bar policy to never show horizontal scroll bars. This just cuts off the label text rather than wrapping the text.
Manually setting the label size - i.e. setting the width from the scroll pane and the height depending on the text. I can't see an easy way to get the correct height of rich HTML text given a fixed width. In any case I'd prefer to have a layout manager that can do the job rather than manually coding preferred sizes.
The one thing I haven't tried yet is creating a custom layout manager. I suspect this might be the right answer but would like to see if any of you have an easier solution that I'm not seeing.

I would like all labels to have the same width (driven by the width of the scroll pane) but vary in height depending on their content
You need to implement the Scrollable interface on your panel and override the getScrollableTracksViewportWidth() method to return true. You will also need to provide default implementations for the other methods of the interface.
Or you can use the Scrollable Panel which provides method that allow you to set the scrolling properties.

How to create a JButton with text on the button left and the icon separated from it on the button right

Basically, I'm trying to make a button that has the text aligned to the left (so I'm using setHorizontalAlignment(SwingConstants.LEFT)) and the image on the right border of the button, far from the text.
I already tried setHorizontalTextAlignment(SwingConstants.LEFT), but that just makes the text go relativity to the left of the icon, which is not exactly what I want, since I needed the icon to be secluded from it.
Also, I can't make any fixed spacing because it's a series of buttons with different texts with different sizes.

I can't make any fixed spacing because it's a series of buttons with different texts with different sizes.
You can dynamically change the spacing with code like:
JButton button = new JButton("Text on left:")
{
#Override
public void doLayout()
{
super.doLayout();
int preferredWidth = getPreferredSize().width;
int actualWidth = getSize().width;
if (actualWidth != preferredWidth)
{
int gap = getIconTextGap() + actualWidth - preferredWidth;
gap = Math.max(gap, UIManager.getInt("Button.iconTextGap"));
setIconTextGap(gap);
}
}
};
button.setIcon( new ImageIcon("copy16.gif") );
button.setHorizontalTextPosition(SwingConstants.LEADING);

This is a derivative of camickr's answer to allow editing in a GUI builder as well as placing it in a dynamic layout. I also removed the UIManager.getInt("Button.iconTextGap") so the gap will shrink to 0 if necessary.
I called it a 'Justified' button in analogy with justified text alignment (stretches a paragraph to left & right by growing width of space characters).
public class JustifiedButton extends JButton {
#Override
public void doLayout() {
super.doLayout();
setIconTextGap(0);
if (getHorizontalTextPosition() != CENTER) {
int newGap = getSize().width - getMinimumSize().width;
if (newGap > 0)
setIconTextGap(newGap);
}
}
#Override
public Dimension getMinimumSize() {
Dimension minimumSize = super.getMinimumSize();
if (getHorizontalTextPosition() != CENTER)
minimumSize.width -= getIconTextGap();
return minimumSize;
}
#Override
public Dimension getPreferredSize() {
Dimension preferredSize = super.getPreferredSize();
if (getHorizontalTextPosition() != CENTER)
preferredSize.width -= getIconTextGap();
return preferredSize;
}
}
This is not exactly production-ready and needs some field-testing. If I find anything, I'll edit the code.
[edit] Now works for vertical text alignments. Also simplified a bit.
[edit2] Also manipulate getPreferredSize to play nice with scroll pane (otherwise it keeps growing and never shrinks again)

You can add a layout manager to your button.
JButton btn = new JButton();
btn.add(new JLabel(text));
btn.add(new JLabel(img));
btn.setLayout(/*best layout choice here*/);
btn.setPreferredSize(new Dimension(x,y));
btn.setMaximumSize(new Dimension(maxX, minY));
btn.setMinimumSize(new Dimension(minX, minY)); //this one is most important when it comes to layoutmanagers
Sorry I can't be much help when it comes to picking out a good layout - But this will eventually get you what you want. Maybe someone else can comment on which one to use.

How to change string length (calculating its width in pixel) when changing window size and strange behaviour of JLabel

I have JLabel which I would like to change its size while I resize the window. When JLabel contains String which is too big, the String should be shortened, with right part visible and adds dots on the left hand side of the String.
My JLabel is inside innerPanel which is a header in middlePanel which is added to outerPanel. So when I resize window I use listener on outerPanel in that way:
outerPanel.addComponentListener(new ComponentListener() {
#Override
public void componentResized(ComponentEvent evt) {
int width = ((JPanel) evt.getSource()).getWidth();
windowSize = width;
refresh();
}
// [...] other not used override methods
});
refresh() repaints view and creates new middlePanel where is called class which creates innerPanel where is located my JLabel:
Public class InnerPanel extends JPanel {
private int maxSize;
String string = "<VERY_LONG_STRING>";
private static final int DEFAULT_INDEND_PIXEL = 70;
public InnerPanel(int windowSize) {
maxSize = windowSize - DEFAULT_INDENT_PIXEL;
createPanel();
}
private createPanel() {
// [...] gridbag and GridBagConstraints implementation
String shortString = countString();
JLabel label = new JLabel(shortString);
add(label,gc);
}
private String countString() {
int index = 0;
boolean toBig = true;
StringBuilder sb = new StringBuilder(string);
while(toBig) {
Rectangle2d rect = // [...] code which creates rectangle around text from sb.toString()
// I have no access to repo at home but if it's important I can paste it tomorrow
if(rect.getWidth() > maxSize)
sb.deleteCharAt(0);
else
toBig = false;
}
return sb.toString();
}
}
That's works fine in general, bacause it do resize JLabel in one step when I enlarge window in width. But the problem is appear when I try to reduce the window in width. In this case componentResized() calculate width step by step (and it's called multiple times), gradually decreases width by some amount of pixels till it reach real window size. It's behave in that way even thow I change window size in one step from maximum size to 800. Whole process is so slow, that it takes around a second to fit string to window size. So it looks bit like an animation.
The problem is very rare to me, bacause width in componentResized() method is calculeted step by step only when I assign windowSize variable.
When I give windowSize fixed size like for example 500 - componentResized() is called only onces - with correct width indicated real window size (!!) - and there's no its step by step decrease!
It's look like width variable which is assigned by ((JPanel) evt.getSource()).getWidth() knows that windowSize is used to dynamically change size of JLabel component even before first call of refresh() method.
If anyone have an idea what is going on here - I will be very appreciate for help.

You may be able to adapt one of the approaches shown here to better effect. As shown here, the ellipsis is supplied by the label's UI delegate via a call to SwingUtilities2.clipString(), which appends the clipString. Rather than re-invent the label UI, use TextLayout to determine the required geometry, prepend the ellipsis, and handle the alignment in a table or list renderer, as shown here.

JLabels to be resized in a GridLayout

I have a very simple Java program (see below). The GridLayout has 20 rows and 4 columns. As you know the elements are supposed to be added horizontally by (GridLayout) definition. However, I get the two elements (labels) placed one above the other, vertically.
I colored them and realised the labels take up the whole row, hence the vertical effect. But then I also used setSize(5,5) with each to make them smaller, however they still take up the whole row. Any advice as to why this happens and how to fix/set smaller size/etc?
public class Sam extends JFrame {
public JButton btn_arr;
public Container c;
public JLabel[] lbl = new JLabel[20];
public Sam()
{
c = getContentPane();
c.setLayout(new GridLayout(20,4));
lbl[1] = new JLabel("Column1");
c.add(lbl[1]);
lbl[2] = new JLabel("Column2");
c.add(lbl[2]);
show();
}
public static void main(String[] args)
{
Sam x = new Sam();
x.setVisible(true);
x.setSize(7500,4500);
}
}

You're only adding two components to the grid so they will fill it up. You need to add more components to the grid as placeholders so that it can place the original JLabels in their proper place, perhaps empty JLabels or JPanels.
As an aside, you should avoid setting the size of any Swing component. Your current size of 7500, 4500 is a bit on the large size.
As a second aside, perhaps you want to use a JTable instead here.
Edit: if you want a GridLayout with 4 columns and variable number of rows, use 0 for your GridLayout row constant:
c.setLayout(new GridLayout(0, 4));
e.g.,
import java.awt.*;
import javax.swing.*;
public class Sam extends JFrame {
public static final int COLUMN_COUNT = 4;
public JButton btn_arr;
public Container c;
public JLabel[] lbl = new JLabel[COLUMN_COUNT];
public Sam() {
c = getContentPane();
c.setLayout(new GridLayout(0, COLUMN_COUNT));
for (int i = 0; i < lbl.length; i++) {
lbl[i] = new JLabel("Column " + (i + 1));
c.add(lbl[i]);
}
}
public static void main(String[] args) {
Sam x = new Sam();
x.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
x.pack();
x.setLocationRelativeTo(null);
x.setVisible(true);
// x.setSize(7500,4500);
}
}
But still I wonder if a JTable wouldn't work better here.

One thing to keep in mind with the GridLayout is it that it is designed to cover the entire containing panel sizing the cells as equally as possible, and elements added to the cells will be expanded to fill the entire cell. So as the cell sizes change, the labels will also change in size. Effectively grid cells force an expansion/contraction in both X and Y direction of all contained elements.
One way to prevent that from happening if you must use the GridLayout is to not add the labels directly to the container that uses the GridLayout, but instead put each label inside a JPanel that uses a FlowLayout (the default) that you can set alignment of either Left, Middle or Right, then add that JPanel to the Grid container. The JPanel will be resized but it will not change the size of the Label.
Or use the GridBagLayout manager. More complex, but once you understand it, it makes life easier. But as Hovercraft mentioned, if what you are trying to do is create a grid with column headers, a JTable might be a better option.