JFrame displaying white bars around content

Question

So I've made a class WindowDisp which extends JFrame:

public class WindowDisp extends JFrame{

    private static final long serialVersionUID = 3245091489595286109L;

    private int height, width;
    private JPanel panel;
    private JLabel mainPane;

    public WindowDisp(int a, int b, int pw, int ph){
        height = a;
        width = b;

        Container c = getContentPane();
        c.setPreferredSize(new Dimension(width, height));
        pack();
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);
        setLocationRelativeTo(null);

        mainPane = new JLabel();
        mainPane.setPreferredSize(new Dimension(pw, ph));
        mainPane.setFont(new Font("Monospaced", Font.PLAIN, 10));

        panel = new JPanel();
        panel.setPreferredSize(getSize());
        panel.add(mainPane);
        add(panel);

        setVisible(true);
        pack();
    }

    public static void main(String[] args){
        WindowDisp win = new WindowDisp(400, 400, 400, 400);
    }
}

From my Main class, I declare a WindowDisp where its height and width are equal to its ph and pw. The problem, however, is that, upon running my program, white 'bars' appear around the default background colored JPanel in the frame. They appear to be padding the panel from the right and the bottom, as though there is space in the frame that the panel is not occupying, although, if my coding is correct, the panel should be the same size as the frame's ContentPane, should it not?

I've found that removing either of the two pack(); commands does not remove these bars, although removing the first one changes them to black, and removing the second widens the one on the right. Of course, removing both of them causes the frame not to be the same size as its ContentPane. Furthermore, removing the add(panel); altogether has no effect.

I can't figure out what in this code is causing that seemingly empty space to appear in my frame, and, again, in my program, all four values being passed to the Window constructor are equal. What seems really strange is that, even if I just remove the add(panel);, nothing at all changes visa vi the white padding. In fact, I can comment out everything from mainPane =... to add(panel); and that doesn't affect it at all.

Answer 1

I can't seem to replicate the issue exactly, but I think I can replicate the desired results...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;

public class WindowDisp extends JFrame {

    private static final long serialVersionUID = 3245091489595286109L;

    private JPanel panel;
    private JLabel mainPane;

    public WindowDisp(int width, int height) {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);

        mainPane = new JLabel();
        mainPane.setBorder(new LineBorder(Color.BLUE));
        mainPane.setFont(new Font("Monospaced", Font.PLAIN, 10));

        panel = new JPanel() {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(width, height);
            }
        };
        panel.setLayout(new BorderLayout());
        panel.setBorder(new EmptyBorder(4, 4, 4, 4));
        panel.add(mainPane);
        add(panel);

        pack();
        setLocationRelativeTo(null);
        setVisible(true);

        System.out.println(getSize());
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                WindowDisp win = new WindowDisp(400, 400);
            }
        });
    }
}

Things that jump out at me (as been of issue)...

• panel.setPreferredSize(getSize()); - The size of the window is generally larger than the window size, this is because the window has decorations which are painted WITHIN the frame boundaries. pack uses the layout information (and preferredSize of the components indirectly) to ensure that the content has the amount of space that it asks for, it then sizes the window around this to accommodate the frame decorations. By calling getContentPane().setPreferredSize you are superseding any information that the layout manager might provide and ignoring the requirements of the other components. This is one of the (many) reasons why we recommend that you NEVER call setPreferredSize, ever...

To reiterate...

Container c = getContentPane();
c.setPreferredSize(new Dimension(width, height));

Forces the viewable space of the window to be set to the width/height values (400x400). This container will no longer be able to react to changes to it's content and will ALWAYS prefer to be 400x400

mainPane.setPreferredSize(new Dimension(pw, ph));

Sets the preferred size of the mainPane to 400x400 (based on your example). Again, it will ALWAYS prefer to be 400x400, but the simple fact of setting the content pane, means that this value is actually ignored...

panel.setPreferredSize(getSize());

Now, the nail in the coffin. This sets the panel to be the same size of the frame, BUT, the frame is larger than the contentPane (400x400 + frame decorations), it is also offset within frame (it won't be positioned at 0x0, but will be offset so that it appears below the frame's title and right border), but could expand beyond the frames boundaries

This combination of issues are all working against you. Instead of worrying about the frame size, worry about the size needs/requirements of the what the frame displays.

Each OS uses different frame decorations, so the actual, physical, frame size will be different on different OSs, but if you focus on the requirements of the content, you won't care

Answer 2

See Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing? (Yes.)

Instead use layout padding and borders for white space. Finally, call pack() to ensure the frame is exactly as large as (the smallest size) it needs to be in order to display the components and white space.

import java.awt.Font;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

public class WindowDisp extends JFrame {

    private JPanel panel;
    private JLabel mainLabel;

    public WindowDisp(int t, int l, int b, int r, String title) {
        super(title);
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        setResizable(false);
        setLocationByPlatform(true);

        mainLabel = new JLabel("Hello Padding!");
        mainLabel.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 10));
        mainLabel.setBorder(new EmptyBorder(t, l, b, r));

        panel = new JPanel();
        panel.add(mainLabel);
        add(panel);

        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {

            @Override
            public void run() {
                new WindowDisp(50, 150, 50, 150, "Window 1");
                new WindowDisp(50, 100, 50, 100, "Window 2");
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

Answer 3

So far the best patch for this annoying issue is the following. Doesn't matter where you call the setResizable(false) method. Just add this piece of code after you setVisible(true).

private void sizeBugPatch() {
    while (frame.getWidth() > yourWidth) {
        frame.pack();
    }
}

Where yourWidth is the width you've set in any of the possible ways, either manually or by overriding setPreferredSize methods. The explanation is quite easy, frame.pack() seems to reset frame.setResizable(boolean b) somehow. You could use an if instead of the while loop but I prefer while to exclude the case the window would still be extra-sized even after a second pack().

Answer 4

One thing I have learned from swing days is to never mix setPreferred... with pack(). You either use one or the other.

Try this code:

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

public class WindowDisp extends JFrame {

    private int height, width;
    private JPanel panel;
    private JLabel mainPane;

    public WindowDisp(int a, int b, int pw, int ph){
        height = a;
        width = b;

        Container c = getContentPane();
//        c.setPreferredSize(new Dimension(width, height));

        mainPane = new JLabel("Hello from Pane");
        mainPane.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 10));

        panel = new JPanel();
//        panel.setPreferredSize(new Dimension(pw, ph));
        panel.add(mainPane);
        c.add(panel, BorderLayout.CENTER);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);
        setLocationRelativeTo(null);
        pack();
        setVisible(true);
    }

    public static void main(String[] args){
        WindowDisp win = new WindowDisp(400, 400, 400, 400);
    }
}

Output: