Best practice to resize JScrollPane

Question

I read some answered questions in this forum (this one for example) where it is strictly recommended to avoid the use of setXXXSize() methods to resize components in swing applications.

So, coming to my problem, i would like to know how to best resize a JScrollPane in order to avoid its parent panel to increase its size without any control.

Before writing some code, i want to describe the real situation, since i will post a "toy example".

In my JFrame i'm currently using a border layout for my content pane. At BorderLayout.CENTER there is a JPanel where i do some custom painting. At BorderLayout.EAST there is a JPanel (say eastPanel) containing some components inside another panel (this panel will be added to eastPanel at BorderLayout.NORTH), and a JScrollPane which contains a JTable (added to eastPanel at BorderLayout.CENTER). This table will have a lot of rows. Since i want eastPanel's height to be the same as centerPanel's height, i need some way to avoid the JScrollPane to increase its size in order to try to display as much rows as possible.

For now i wasn't be able to find another solution apart from calling setPreferredSize on the eastPanel containing the scrollpane, but i have to admit that i hate this kind of solution.

Sample Code

In this code sample i added some random labels at the north of eastPanel and inside the JScrollPane, since my purpose was to post a short sample of code. However, the situation is very similar to the one i have described above. I wasn't be able to solve my problem without using this "terrible" line of code :

eastPanel.setPreferredSize(new Dimension(eastPanel.getPreferredSize().width, centerPanel.getPreferredSize().height));

I would like to avoid a more complex layout for a simple situation like this. Am i missing something ? Also, is setting that empty border an acceptable way to set the size of the panel where i will do some custom painting?

Code :

import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class Test
{
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                try {                       UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    new TestFrame().setVisible(true);
                }
                catch(Exception exception) {
                    JOptionPane.showMessageDialog(null, "Fatal error while initialiing application", "Error", JOptionPane.ERROR_MESSAGE);
                }
            }
        });
    }
}
class TestFrame extends JFrame 
{
    public TestFrame() {
        super("Test");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JPanel pane = new JPanel(new BorderLayout(20, 0));
        pane.setBorder(new EmptyBorder(20, 20, 20, 20));
        JPanel centerPanel = new JPanel();
        centerPanel.setBackground(Color.WHITE);
        centerPanel.setBorder(new EmptyBorder(400, 400, 0, 0));
        // centerPanel.setPreferredSize(new Dimension(400, 400));
        JPanel eastPanel = new JPanel(new BorderLayout(0, 20));
        JPanel labelsContainer = new JPanel(new GridLayout(0, 1));
        for(int i=0;i<7;i++) labelsContainer.add(new JLabel(String.valueOf(i)));
        eastPanel.add(labelsContainer, BorderLayout.NORTH);
        JPanel moreLabelsContainer = new JPanel(new GridLayout(0, 1));
        for(int i=7;i<70;i++) moreLabelsContainer.add(new JLabel(String.valueOf(i)));
        JScrollPane scroll = new JScrollPane(moreLabelsContainer, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        eastPanel.add(scroll, BorderLayout.CENTER);
        eastPanel.setPreferredSize(new Dimension(eastPanel.getPreferredSize().width, centerPanel.getPreferredSize().height));
        pane.add(centerPanel, BorderLayout.CENTER);
        pane.add(eastPanel, BorderLayout.EAST);
        setContentPane(pane);
        pack();
        setLocationRelativeTo(null);
    }
}

Thanks for your help !

Answer 1

I am not aware of a layout manager that restricts the height of the panel based on the height of a specific component in the panel.

One way is to customize the behaviour of the parent panel that contains the two child components.

The code might be something like:

@Override
public Dimension getPreferredSize()
{
    Dimension d = super.getPreferredSize();

    BorderLayout layout = (BorderLayout)getLayout();
    Component center = layout.getLayoutComponent(BorderLayout.CENTER);

    int centerHeight = center.getPreferreidSize().height;

    if (d.height > centerHeight)
        d.height = centerHeight;

    return d;
}

This approach will allow for dynamic calculation of the height based on the component in the center.

Another option is to write you own layout manager. Then you can control this type of logic from within the layout manager.

Also, is setting that empty border an acceptable way to set the size of the panel where i will do some custom painting?

I override the getPreferredSize() to return the appropriate dimension.

By using the EmptyBorder you lose the ability to add a true Border to the panel, so I wouldn't recommend it.