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)
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