Question

I’m still trying to learn how layout managers work. I made a Frame with two JPanels.
The first one contains a textArea with a boxLayout.
The second one contains a flow layout with a button.

I set the preferredSize of each panel accordingly, packed them, but got unexpected results.

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

public class LayoutMgrTest
{
    public static void main(String[] args)
    {
        TableBasic frame = new TableBasic();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.setVisible(true);


        frame.getContentPane().setLayout(new GridLayout(2,1));

        JPanel controlPane = new JPanel();
        JPanel buttonPane = new JPanel();

        controlPane.setLayout(new BoxLayout(controlPane, BoxLayout.PAGE_AXIS));
        controlPane.setPreferredSize(new Dimension(200, 200));
        controlPane.add(new JScrollPane(new JTextArea()));

        buttonPane.setLayout(new FlowLayout(FlowLayout.LEFT));
        buttonPane.setPreferredSize(new Dimension(100,20));
        buttonPane.add(new JButton("Button1"));
        buttonPane.add(new JButton("Button2"));

        frame.getContentPane().add(controlPane, BorderLayout.NORTH);
        frame.getContentPane().add(buttonPane, BorderLayout.SOUTH);
        frame.setSize(new Dimension(500,500));
        frame.pack();
    }
}

Whatever I do, if I use a grid Layout, it seems to always allocate half of the available space to each control. I have been told that:

The height of each row is dependent on the height of each component
added in each row.

The buttonpane’s height is 20. It’s allocating much more than that to it:

What’s wrong with this code?
I would like to leave the two JPanels intact please. It’s easy to simply add the textbox and the buttons directly to the frame, but I need to do it with JPanels (because I will be adding borders and other things).

Answer 1

That’s the result of using GridLayout as layout manager. Change it to BorderLayout:

frame.getContentPane().setLayout(new BorderLayout());

For example, this code (I changed a little as possible from the original):

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

public class LayoutMgrTest
{
    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        //frame.setVisible(true);   
        //frame.getContentPane().setLayout(new BorderLayout());

        JPanel controlPane = new JPanel();
        JPanel buttonPane = new JPanel();

        controlPane.setLayout(new BoxLayout(controlPane, BoxLayout.PAGE_AXIS));
        controlPane.setPreferredSize(new Dimension(200, 200));
        controlPane.add(new JScrollPane(new JTextArea()));

        buttonPane.setLayout(new FlowLayout(FlowLayout.LEFT));
        buttonPane.setPreferredSize(new Dimension(100,40));
        buttonPane.add(new JButton("Button1"));
        buttonPane.add(new JButton("Button2"));

        frame.add(controlPane, BorderLayout.NORTH);
        frame.add(buttonPane, BorderLayout.SOUTH);
        //frame.setSize(new Dimension(500,500));
        frame.pack();
        frame.setVisible(true);
    }
}

Generates this frame: