Name: dk106046 Date: 05/20/2004

OPERATING SYSTEM(S):
Win32, Windows 2000

FULL JDK VERSION(S):
java version "1.5.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta-b32c)
Java HotSpot(TM) Client VM (build 1.5.0-beta-b32c, mixed mode)

java version "1.4.2_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_04-b05)
Java HotSpot(TM) Client VM (build 1.4.2_04-b05, mixed mode)



- Minimal source code that demonstrates the problem
import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
                                                                        
import javax.swing.*;
                                    
public class TextAreaTest extends JDialog {
                                                                        
    public static void main(String[] args) {
        TextAreaTest test = new TextAreaTest();
        test.show();
    }
                                                                        
    public TextAreaTest(){
        // Add a text area to the panel
                                                                        
        JTextArea textArea = new JTextArea("Now is the time for all good
 men to come to the aid...");
        textArea.setLineWrap(true);
        JPanel panel = new JPanel();
        panel.setLayout(new GridBagLayout());
        GridBagConstraints con = new
GridBagConstraints(2,2,GridBagConstraints.REMAINDER,1,0.5,0.0,GridBagCon
straints.NORTHWEST,GridBagConstraints.BOTH,new
 Insets(0,0,0,0),0,0);
        panel.add(textArea,con);
                                                                        
        // Add a table
        JTable table = new JTable(5,2);
        con = new
GridBagConstraints(1,6,3,3,1.0,1.0,GridBagConstraints.NORTHWEST,GridBagC
onstraints.BOTH,new
 Insets(0,0,0,0),0,0);
        JScrollPane sp = new JScrollPane(table);
                                                                        
        panel.add(sp,con);
                                                                        
        JButton button = new JButton("Remove");
        con = new
GridBagConstraints(4,6,1,1,0.0,0.0,GridBagConstraints.NORTHWEST,GridBagC
onstraints.NONE,new
 Insets(0,0,0,0),0,0);
        panel.add(button,con);
                                                                        
                                                                        
        JPanel buttonPanel = new JPanel();
        button = new JButton("OK");
        buttonPanel.setLayout(new GridBagLayout());
        con = new
GridBagConstraints(1,1,1,1,0.0,0.0,GridBagConstraints.NORTHWEST,GridBagC
onstraints.NONE,new
 Insets(0,2,0,2),0,0);
        buttonPanel.add(button,con);
                                                                        
        con = new
GridBagConstraints(2,9,GridBagConstraints.REMAINDER,1,0.0,0.0,GridBagCon
straints.SOUTHEAST,GridBagConstraints.NONE,new
 Insets(0,0,0,0),0,0);
        panel.add(buttonPanel,con);
                                                                        
        JScrollPane sPane = new JScrollPane(panel);
        Container c = this.getContentPane();
        c.add(sPane);
        Window window = this;
        window.pack();
                                                                        
        this.setDefaultCloseOperation(JDialog.DO_NOTHING_ON_CLOSE);
        window.addWindowListener(new WindowAdapter()
        {
         public void windowClosing(WindowEvent e)
         {
             System.exit(0);
         }
        }
        );
    }
}

- Exact steps to reproduce
If you run this test you will see an infinite loop in the layout of the panel. The panel comes up and shows the controls but the panel keeps getting bigger and bigger forever. There is a scroll pane in the contentpane so the window doesn?t keep growing just the panel in the scroll pane.

The infinite loop seems to be caused by a combination of controls and grid bag layout parameters. GridBagConstraints.REMAINDER on the textarea and the button panel seem to be important. As does GridBagConstraints.BOTH on the textarea. If you remove the table it works and if you just remove the scroll pane from the table it works. Also if you remove the "Remove" button it works. This seems to be the minumum amount of controls which cause it to fail. If you change anything it will likely work.

- Other Findings
What is happening is that each time the components are laid out the GribBagLayout's layout info is recalculated with a new, increasing width for the textarea. This change in the textarea's width causes the layout to have to be revalidated which means that a ComponentWorkRequest is queued and the components are layed out again. This keeps looping round due to the textarea's width increasing each time it is calculated by GridBagLayout.getLayoutInfo (which is called by GridBagLayout.arrangeGrid amongst other things).

The textarea's width is growing since GridBagLayout.getLayoutInfo steps through the children components, ie, the JTextArea, the JScrollPane holding the JTable, etc, building up the info, based on the constraints set by the user, as follows:

- First for the JTable, which spreads across columns 2 to 4, since no weightings for the columns have been calculated yet the weighting of 0.5 for the textarea is placed in the last column in the textarea's region, ie, weightX(4)=0.5, and all other weightings in this region are left at 0. This means that the extra space needed for the textarea (the current width of the textarea - the minWidth of all the cells in the textareas region) is placed entirely in column 4, ie, minWidth(4).

-Similarly for the JScrollPane containing the JTable, which spreads across columns 1 to 3, only weight(3) has a non-zero value, 1.0, and so all the extra space for this component is placed entirely in column 3.

At the end of this minWidth(2)=0, minWidth(3)=current width of the table's scrollpane, and minWidth(4)=current width of the table. Since the JTextArea's fill field is GridBagConstraints.BOTH the width of the textarea is stretched to fit the sum of all the minWidth's for columns 2,3 and 4, ie, this means the current width of the table's scrollpane plus the current width of the textarea. Therefore the textarea's width is continuously growing by the width of the table's scrollpane.

Thus looks like the value of width is being calculated depending on the weight. Thus it looks like there is a problem in the logic of calculating the width in the code. Since this problem exists across all the Sun JDK versions it would be expected to be addressed in the development and update releases.

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