How do you stop a JLabel changing its size when its text changes?

Question

I'm generating some JComponents in code and using the GridBag layout to arrange them. My layout consists of 12 rows and 3 columns, with each row consisting of a JSlider, a JCheckBox and a JLabel. Here's the code I'm using to generate the UI:

final int NUM_MOTORS = 12;

// This is the panel I'm adding the components to.
pnlMotorSliders.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();

for (int i = 0; i < NUM_MOTORS; ++i) {
    c.gridy = i;

    // Create the slider
    JSlider slider = new JSlider(SwingConstants.HORIZONTAL, 10, 4085, 10);
    c.fill = GridBagConstraints.HORIZONTAL;
    c.gridx = 0;
    c.weightx = 0.9;
    pnlMotorSliders.add(slider, c);

    // Create the checkbox
    JCheckBox checkBox = new JCheckBox();
    checkBox.setOpaque(true);
    checkBox.setBackground(Color.blue);
    c.fill = GridBagConstraints.NONE;
    c.gridx = 1;
    c.weightx = 0.1;
    pnlMotorSliders.add(checkBox, c);

    // Create the current label
    JLabel label = new JLabel("0");
    label.setBorder(BorderFactory.createLineBorder(Color.red));
    c.fill = GridBagConstraints.HORIZONTAL;
    c.gridx = 2;
    c.weightx = 0.2;
    pnlMotorSliders.add(label, c);
}

The problem I'm having is that when I set the text in any of the JLabels, they change their width and affect the rest of the layout, even if the width of the text that I'm setting appears to be much smaller than the width of the JLabel. The following two screenshots demonstrate what I mean (the red and blue borders were for debugging purposes):

I've set the text on the bottom JLabel to "-12". Even though the JLabel appears to be much wider than the text, it has changed its size, affecting the rest of the layout.

Why is this happening and what can I do to prevent it?

Solution 1

You can fix the size of the labels by setting the minimum, prefered and maximum size:

label.setMinimumSize(width, height);
label.setPreferedSize(width, height);
label.setMaximumSize(width, height);

Also make sure to set the GridBagConstraints#fill to NONE, although I am not sure if that is still neccessary (I think it is).

EDIT: btw, to get rid of those nasty dashed lines around the focused Component, you can just set it to be not focusable:

slider.setFocusable(false);

Solution 2

The set-the-preferred-size solution works only if you don't have the components horizontally fill their bag in the GridBagLayout.

Another solution is to remove the weight you have placed on components in that column of your GridBagLayout. You can then control the column width manually. An easy way to do so (at design time) is to place a JLabel in the column with zero height and the specific width you desire.

Why is this? You need to dig into how GridBagLayout works:

The GridBagLayout sizes its columns based on the space required, and then uses the weights to allocate the "left over" space so that the resulting column widths then add up to the total width of the panel. The space required for each column is computed by finding the widest of the components in that column.

The space required for each component is determined by asking it what width it would prefer. In your case, a JLabel with "0" is smaller than a JLabel with "-12" and so the column is changing size.

The left over space is allocated based on the horizontal weights assigned to components in each column. The weights are totaled and percentages for each column are determined based on that column's percent of the total.

The column size is determined based on the space required PLUS the left over space. So, if all your components in the column have no weight then you'll not get any left over space, and hence not get dynamic changes.

A third solution is to just not use GridBagLayout.

Comments

[Amr Bekhit]

This doesn't seem to work. I added the following line when generating the label: label.setSize(new Dimension(50, label.getPreferredSize().height)); and set the GridBag Fill to NONE. Unfortunately, the label ignores my dimension, uses it's default size and changes its width when the text changes. I tried setting the label size both before and after I added it to the parent container.

[Amr Bekhit]

Thanks, this seems to work. I experimented a little bit and found that I only need to call setPreferredSize to set the JLabel size. The other two don't seem to make a difference. Also, thanks for the tip on setFocusable. The question I have now is why did I face this problem in the first place? With my original layout, the label was wider than it needed to be, yet it still changed its width when the text changed, even though the text was clearly much smaller than the label.

[npe]

I've edited the original answer. Did some coding and it seems, that just setting preferredSize is enough (no matter what the fill value is). Check if it works for you, I'll post some code if you need.

[brimborium]

@AmrBekhit Yes, setPreferredSize is enough, if there is that space available. But if not, other Components will take it away and the label will be forced to be smaller (or bigger). But for your application, I guess setPreferredSize is enough. The reason why it changed is that when not set, the preferred size of the label is depending on the text it is displaying. Btw: label.setHorizontalAlignment(JLabel.RIGHT); migh be helpful too. ;)

[Catalina Island]

If it's not focusable, how do you adjust it from the keyboard?

[brimborium]

@CatalinaIsland You can't (unless you create a KeyListener that changes it indirectly). But in my opinion, a JSlider should be modified with the mouse and not the keyboard anyway. ;)

[Amr Bekhit]

@brimborium Hmm...it still doesn't make sense. The preferred width of the label should have been less than than the width the layout manager had allocated for it (the red borders in my image should show that). If the label was resizing itself based on the preferred size, then the label should have become smaller than it's initially allocated space, not larger. (continued below)

[Amr Bekhit]

It's almost like when the label is first added to the layout manager, the manager adds fixed padding along the label's width based on its initial preferred size to make the label fill the required space. However, if the label's text changes (and thus the preferred size), rather than recalculating the amount of padding required, the layout manager uses the same fixed padding calculated initially, which is what causes the label to change size.

[brimborium]

@AmrBekhit I didn't say that the text will say how large the JLabel will be, but it has some saying. Using weight, the GridBagLayout will weight the "needs" of every component and distribute the available space according to those values. If the "needs" (the preferred size) is different, so is the final width of the component.

[brimborium]

And yes, Java Layout is not really nice to do. If you are looking for an alternative: MigLayout is a very nice layout manager for Swing Layouts. It takes a bit to get the hang of it, but I think it's worth it.

[kleopatra]

no, whatever the problem, tweaking a component's sizing hints is not a solution ... instead, use a decent LayoutManager

[kleopatra]

no, whatever the problem, tweaking a component's sizing hints is not a solution ... instead, use a decent LayoutManager

[brimborium]

@kleopatra I told him to use MigLayout (right before your comment). But the question asks for a solution with GridBag LayoutManager. Thanks for your comment though, +1.