Auto scrolling JTextAreas

Question

Hi,
I am having an infuriating problem with my JTextArea which hopefully someone can help me with.
On my GUI I have a JTextArea in a JScrollPane which is uneditable as it
is there purely to give the user feedback. The user presses a button
and the program happily does its thing creating datafiles and other
such things and all the while telling the user what it is up to.
The code I use to update the display is this:
public void updateText(String str)
    textarea.append(string + "\n");
    textarea.paintImmediately();
    textarea.scrollRectToVisible(textarea.modelToView(
                      textarea.getDocument().getLength());
}This works fine until the text reaches the bottom of the JTextArea
because what ever the last line of text is, it gets repeated evertime
it scrolls until the program stops updating the display at which point
the text changes to what it should be. So for example, if the last text
was "This is rubbish" before it starts scrolling then the
display would look like this...
This is rubbish
This is rubbish
This is rubbish
This is rubbish....(and so on until the end where it changes to the proper text).
One thing I have noticed is that the last line in the JTextArea before
scrolling starts has about the bottom two rows of pixels missing from
the text, could this be causing the scrolling to mess up. I have tried
making the JTextArea double buffered and swapping the order of the
scrolling and the paintImmediatly.
I am really stuck and have searched through the forums trying all the
usual suggestions for scrolling such as setting the caret position but
this seems to be the only one that make the JTextArea scroll, albeit
with a messed up display.
Please can someone help me, this is really bugging me. (No pun intended).
Cheers Jim.

Answer 1

Check this code
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
class Test extends JFrame implements ActionListener
     static int nCount = 0;
     JTextArea m_areaTest = null;
     JButton m_btnTest = new JButton("Add");
     public Test()
          m_areaTest = new JTextArea(10,30);
          JScrollPane scrollTest = new JScrollPane(m_areaTest);
          m_areaTest.setLineWrap(true);
          getContentPane().setLayout(new FlowLayout());
          getContentPane().add(scrollTest);
          getContentPane().add(m_btnTest);
          m_btnTest.addActionListener(this);
          addWindowListener(new WindowAdapter()
               public void windowClosing(WindowEvent e)
                    dispose();
                    System.exit(0);
     public static void main(String args[])
          System.out.println("Starting CopyPaste...");
          Test mainFrame = new Test();
          mainFrame.setSize(400, 400);
          mainFrame.setTitle("CopyPaste");
          mainFrame.setVisible(true);
     public void actionPerformed(ActionEvent e)
          if(e.getSource() == m_btnTest)
               m_areaTest.append("This is rubbish"+ nCount+ "\n");
               nCount++;
               //m_areaTest.paintImmediately();   
               //bm_areaTest.scrollRectToVisible(m_areaTest.modelToView(textarea.getDocument().getLength()));
}regards
Praveen