GridBagLayout/JScrollPane Bug Explained- Is there a workaround?

[Josh Rehman]

Ever seen a jumpy GridBagLayout? Ever wonder why? This demo code explains it, and tracks root cause. The code to reproduce is self-explainitory. The first class is the one that demos the problem. The second is a utility class I use in the first, and is not relevant to the problem.

import java.awt.BorderLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
/**
 * There is a bug in GridBagLayout where components are jumpy.
 * Looking closer, it is apparent that this bug appears when the
 * preffered size of a component is larger than the container. This
 * can happen if there is lots of text in a text component, for example,
 * and/or the container is resized.
 *
 * This class is an attempt to find the smallest possible class that
 * demonstrates this bug.
 *
 * The first bug that is apparently related, is when you add two text
 * fields. Try to make the frame smaller, and they collapse. Add some
 * text and jiggle the frame, and they collapse. The work around is
 * to assign a horiz weight to each display area. (Bug 1, 1.1)
 *
 * This isn't quite the behavior I am seeing, so we will continue. In
 * my particular case, horizontal resizing is resulting in a vertical
 * collapse of the last row, which is a text area in a scrollpane.
 * Let's try to reproduce this.
 *
 * We can reproduce this (Bug2). However, it is the relationship between
 * the scrollpane and Gridbag. Other components do not have anything
 * to do with this problem. It also appears that this problem appears
 * when the bounds of the container are smaller than the preffered size
 * of the text field within the scrollpane, and so the scrollpane
 * switches on. For some reason, the scrollpane isn't layed out
 * properly when it switches modes. The work around is to set weightx =
 * weighty = 1.0 and fill = BOTH.
 *
 * A problem remains. What if we want a TextArea in a ScrollPane that
 * doesn't get any taller? You might think you could embed the element
 * on a container that doesn't give the component any extra vertical,
 * like the NORTH portion of a border layout, or another GridBag with
 * weighty = 0 and fill = NONE, but you would be wrong. This doesn't
 * fix the problem. (Bug3)
 *
 * Apparently there is a constraint on Swing layouts that a JScrollPane
 * MUST fill it's display area, AND the display area MUST have some
 * non-zero weight. Further, this holds for all containing containers!
 *
 * You cannot create a text area that scrolls vertically,
 * but which will only grow horizontally. This seems needless,
 * and pisses me off.
 *
 * @author Josh Rehman - Nov 1, 2002
 */
public class GridBagBug {
    public static void main(String[] args) {
        GridBagConstraints c = new GridBagConstraints();
        // Bug1: Horizontal collapse
        JPanel bug1 = new JPanel();
        bug1.setLayout(new GridBagLayout());
        bug1.add(new JTextField("some text"));
        bug1.add(new JTextField("other text"));
        DefaultFrame.show("GridBagBug 1.0", bug1, true);
        //Bug1.1 Explicit Horizontal Collapse
        JPanel bug1_1 = new JPanel();
        bug1_1.setLayout(new GridBagLayout());
        c = new GridBagConstraints(
            c.RELATIVE,     //gridx
            c.RELATIVE,     //gridy
            1,     //gridwidth
            1,              //gridheight
            1.0,            //weightx
            0.0,            //weighty
            c.WEST,       //anchor
            c.HORIZONTAL,   //fill
            new Insets(0,0,0,0),           //insets
            0,              //ipadx
            0               //ipady
        );
        bug1_1.add(new JTextField("some text"), c);
        c = new GridBagConstraints(
            c.RELATIVE,     //gridx
            c.RELATIVE,     //gridy
            c.REMAINDER,     //gridwidth
            1,              //gridheight
            1.0,            //weightx
            0.0,            //weighty
            c.WEST,       //anchor
            c.HORIZONTAL,   //fill
            new Insets(0,0,0,0),           //insets
            0,              //ipadx
            0               //ipady
        );
        bug1_1.add(new JTextField("other text"), c);
        DefaultFrame.show("GridBagBug 1.1", bug1_1, true);
        // Bug2: Vertical collapse
        JPanel bug2 = new JPanel();
        bug2.setLayout(new GridBagLayout());
        c = new GridBagConstraints(
            c.RELATIVE,     //gridx
            c.RELATIVE,     //gridy
            c.REMAINDER,     //gridwidth
            1,              //gridheight
            1.0,            //weightx
            0.0,            //weighty
            c.WEST,       //anchor
            c.HORIZONTAL,   //fill
            new Insets(0,0,0,0),           //insets
            0,              //ipadx
            0               //ipady
        );
        bug2.add(new JTextField("some text"), c);
        c = new GridBagConstraints(
            c.RELATIVE,     //gridx
            c.RELATIVE,     //gridy
            c.REMAINDER,     //gridwidth
            1,              //gridheight
            0.0,            //weightx
            0.0,            //weighty
            c.WEST,       //anchor
            c.BOTH,   //fill
            new Insets(0,0,0,0),           //insets
            0,              //ipadx
            0               //ipady
        );
        bug2.add(new JScrollPane(new JTextArea("other text\nwhich is\nthere\nyeah")), c);
        DefaultFrame.show("GridBagBug 2", bug2, true);
        JPanel bug3 = new JPanel();
        bug3.setLayout(new BorderLayout());
        bug3.add(bug2, BorderLayout.NORTH);
        DefaultFrame.show("GridBagBug 3", bug3, true);
    }
}
  

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JTextField;
/**
 * A simple class for creating frames.
 * Typical usage is outlined in the main method, but it looks like this:
 * DefaultFrame frame = new DefaultFrame("A Button", new JButton("A Button"));
        frame.go(true);
   
   Alternatively you could say DefaultFrame.show(title, component, pack);
 * @author Josh Rehman
 */
public class DefaultFrame extends JFrame {
    public DefaultFrame(){
        this("Default Frame", null);
    }
    public DefaultFrame(String title){
        this(title, null);
        
    }
    public DefaultFrame(String title, JComponent c){
        super(title);
        if (c != null){
            getContentPane().add(c);
        }
        setSize(600, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    
    protected void go(boolean pack){
        if (pack) pack();
        setVisible(true);
    }
    
    public static JFrame show(String title, JComponent c, boolean pack){
        DefaultFrame result = new DefaultFrame(title, c);
        result.go(pack);
        return result;
    }
    
    public static void main(String[] args) {
        DefaultFrame frame = new DefaultFrame("A Demo", new JTextField("hi\nhello\nwassup"));
        frame.go(true);
    }
}
  

[Josh Rehman]

Found something in the bug parade that looks related. Please join the Sun JDC and vote for this bug! The more votes, the more likely this bug will get fixed!
http://developer.java.sun.com/developer/bugParade/bugs/4760103.html