JDK-4202291 : long lines in wrapped JTextArea causes severe performance degradation
  • Type: Bug
  • Status: Resolved
  • Resolution: Fixed
  • Component: client-libs
  • Sub-Component: javax.swing
  • Priority: P4
  • Affected Version: 1.1.7,1.2.2,1.3.0,1.4.2
  • OS: solaris_2.5.1,windows_95,windows_nt,windows_2000
  • CPU: x86,sparc
  • Submit Date: 1999-01-12
  • Updated Date: 2005-04-11
  • Resolved Date: 2004-12-01
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JDK 6
6 b14Resolved
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Description
Name: krT82822			Date: 01/11/99


JTextArea setLineWrap causes severe performance degradation

If line wrap is true, and a large line of text is set into the text area, then painting performance can suffer if the line of text doesn't end in a carriage return. The example program demonstrates the problem. After pressing the 'Bad Fill' button, try selecting text or resizing the window and notice that it takes a lot longer than it  should. This bug is new to Swing-1.1 and doesn't exist in Swing-1.0.3.

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

/**
 * Demonstrates a performance bug in JTextArea if line wrap
 * is true, and a large line of text is entered. Oddly, if
 * the line of text ends in a carriage return, performance
 * isn't affected.
 */
public class JTextAreaBug extends JPanel
{
    JTextArea text = new JTextArea();
  
    public static void main( String[] args )
    {
        JFrame frame = new JFrame( "JTextArea Bug" );
        frame.addWindowListener(
            new WindowAdapter()
            {
                public void windowClosing( WindowEvent evt )
                {
                    System.exit( 0 );
                }
            });

        frame.getContentPane().add( new JTextAreaBug(), BorderLayout.CENTER );
        frame.setSize( 400, 300 );
        frame.setVisible( true );
    }
    
    public JTextAreaBug()
    {
        super( new BorderLayout() );
        text.setLineWrap( true );
        
        add( new JScrollPane( text ), BorderLayout.CENTER );

        JButton goodFill = new JButton( "Good Fill" );
        JButton badFill = new JButton( "Bad Fill" );
        JPanel buttonPanel = new JPanel();
        buttonPanel.add( goodFill );
        buttonPanel.add( badFill );
        add( buttonPanel, BorderLayout.SOUTH );
        
        goodFill.addActionListener(
            new ActionListener()
            {
                public void actionPerformed( ActionEvent evt )
                {
                    fillText( true );
                }
            });
        badFill.addActionListener(
            new ActionListener()
            {
                public void actionPerformed( ActionEvent evt )
                {
                    fillText( false );
                }
            });
    }
   
    /**
     * Fills the text field with bunch of characters. If 
     * addCarriageReturn is true, then a carriage return
     * is added at the end.
     */
    void fillText( boolean addCarriageReturn )
    {
        final int SIZE = 27000;
        StringBuffer buff = new StringBuffer( SIZE + 1 );
        for( int i = SIZE - 1; i >= 0; i-- )
            buff.append( "x" );
        
        if( addCarriageReturn )
            buff.append( '\n' );
        
        text.setText( buff.toString() );
    }
}
(Review ID: 47890)
======================================================================
###@###.### 11/1/04 10:39 GMT

Comments
SUGGESTED FIX http://sa.sfbay.sun.com/projects/swing_data/mustang/4202291.4 ###@###.### 11/4/04 11:22 GMT
2004-11-04

EVALUATION The layout of each logical line (i.e. area in the model that ends with a newline) is computed in the view on the fly. If the number of wrapped pieces in the view is large is is effectively recomputing all of the pieces each time it paints. Attempting to display one logical line wrapped into hundreds or thousands of pieces will result in very low performance with the current implementation. This could be fixed by switching the views used to display a wrapped JTextArea to ZoneView and ParagraphView and fixing bug4250864. timothy.prinzing@eng 1999-09-17 Name: pzR10082 Date: 04/30/2004 Currently a line is wrapped each time it is painted, or viewToModel/ modelToView is called. This makes a significant slowdown in when there are many long lines. A solution is to cache calculated line break positions in an array, and reuse them until they become invalid. ###@###.### ======================================================================
2004-09-27

WORK AROUND Name: krT82822 Date: 01/11/99 always add a carriage return at the end of a long line of text. ====================================================================== ###@###.### 11/4/04 11:22 GMT
4-11-04 00:00:00