How to make a JPanel expand to max width in another JPanel

java swing jpanel layout-manager boxlayout

49,573

Solution 1

If using a BorderLayout and the b panel is in the SOUTH or PAGE_END it does fill the entire width.

Solution 2

The easiest way would be to use another layout manager such as GridLayout that automatically sizes components to fill the parent container.

myPanel.setLayout(new GridLayout(0, 1));

Solution 3

You can use GridBagLayout, for that, using

gridBagObject.fill = GridBagConstraints.HORIZONTAL

One example for your help, relating to GridBagLayout.

As asked in comments, related to that

The BoxLayout is another alternative, that respects the preferred sizes of the components. You can try that if GridBagLayout is that tough :-)

Code with GridBagLayout, for more clarity :

import javax.swing.*;
import java.awt.*;

/**
 * Created with IntelliJ IDEA.
 * User: Gagandeep Bali
 * Date: 1/10/13
 * Time: 7:43 PM
 */
public class GridBagExample
{
    private void displayGUI()
    {
        JFrame frame = new JFrame("GridBagLayout Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        CustomPanel topPanel = new CustomPanel(Color.BLUE.darker().darker());
        CustomPanel middlePanel = new CustomPanel(Color.CYAN.darker().darker());
        CustomPanel bottomPanel = new CustomPanel(Color.DARK_GRAY);

        JPanel contentPane = new JPanel();
        contentPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new GridBagLayout());

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.anchor = GridBagConstraints.FIRST_LINE_START;
        gbc.fill = GridBagConstraints.VERTICAL;
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.weightx = 1.0;
        gbc.weighty = 0.3;

        contentPane.add(topPanel, gbc);

        gbc.gridy = 1;
        contentPane.add(middlePanel, gbc);

        gbc.gridy = 2;
        gbc.fill = GridBagConstraints.BOTH;
        contentPane.add(bottomPanel, gbc);

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String... args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new GridBagExample().displayGUI();
            }
        });
    }
}

class CustomPanel extends JPanel
{
    public CustomPanel(Color backGroundColour)
    {
        setOpaque(true);
        setBackground(backGroundColour);
    }

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(200, 150));
    }
}

OUTPUT :

GridBagExampleOutput

49,573

Author by

Martin Nielsen

Updated on July 06, 2020

Comments

Martin Nielsen almost 4 years
I feel I need to rephrase the question a bit.

Updated question below.

I have a JPanel that contains:
```
myjpanel.setLayout(new BoxLayout(selectors, BoxLayout.PAGE_AXIS));
```
It contains the following three panels:

JPanel with fixed size 'x' and 'y'

JPanel with no fixed size

JPanel with no fixed size and small height

The second JPanel contains a JTable so it expands to fill the full height and pushes the bottom panel all the way down, as expected.

Like this:
```
t
t
m
m
m
m
m
b
```
t = top panel, m = middle panel, b = bottom panel.

That works. But the bottom panel does not feel like filling the entire width of the parent which is a problem.
```
ttt
mmm
 b 
```
I would like either this, where the panel fills the entire width:
```
ttt
mmm
bbb
```
or this, where the bottom panel is left centered:
```
ttt
mmm
b
```
Old question below:

I have a JPanel that contains:
```
.setLayout(new BoxLayout(selectors, BoxLayout.PAGE_AXIS));
```
Within it, there are three more JPanels. The first two are of fixed size and the middle one isn't.

I want my bottom panel to take only the height it needs, but uses all the available width of the outer JPanel.

I have tried using glue but to no avail, and I would rather not set preferred and min/max sizes. Is there a way to tell the component to "Fill the entire parents width" using just the layout manager and framework. I would rather not start to do hacks like setting sizes and overriding methods.

Note: I can't put any glue or filler in the inner panel, only the outer panel and its layout manager can be modified.

Attempt 1:

Using myPanel.setLayout(new GridLayout(3, 1)); did not produce the expected results. It made a grid like this:
```
XX
 X
```
But I expected:
```
X
X
X
```
Attempt 2:

Using myPanel.setLayout(new GridLayout(0,1)); did not produce the expected results. It made a grid like this:
```
x
x
x
```
But all panels were of the same size, ignoring the restraints.
Adam Dyga over 11 years

... or FormLayout from JGoodies
Martin Nielsen over 11 years

Would that screw with the two fixed size components that shares the container?
Martin Nielsen over 11 years

Alternatively i would be more than satisfied by left aligning the inner component as well, but i cant seem to do so as the setAllignmentX method doesn't do squat
Martin Nielsen over 11 years

I tried GridLayout, it did not arrange the components vertically but placed them 2 in the top and 1 in the buttom
nIcE cOw over 11 years

@MartinNielsen : You have to use it like new GridLayout(0, 1);
Martin Nielsen over 11 years

GridLayout makes all the components equally large. The idea was that the bottom one should only be sized after its internal components.
Martin Nielsen over 11 years

Is there no simpler way? Keep in mind its just three components in a vertical row. It should not be required to go to the big guns. I just want my bottom component to use the full width. Surely i don't need to go gridbagconstraints for this?
nIcE cOw over 11 years

@MartinNielsen : Please have a look at BoxLayout, as edited in my answer.
Martin Nielsen over 11 years

Ehm. I don't think you read the question. I AM using BoxLayout!
Martin Nielsen over 11 years

BorderLayout works perfectly. Thank you, and damn BoxLayout:)