Re: How to append to textarea immediately?
Sal wrote:
public void init() {
Container cp = getContentPane();
cp.setBackground( darkGreen );
cp.setLayout( new FlowLayout() );
textArea = new JTextArea(30, 40);
scrollPane = new JScrollPane();
cp.add ( new JScrollPane( textArea ) );
textArea.setEditable( false );
textArea.append( "Begin counting " + nbrOfTimes +" \n" ); //
<------ look here
int ctr = 0;
while( ++ctr < nbrOfTimes );
textArea.append( "End counting " + ctr +" \n" );
Swing code like that above must be executed on the EDT, or it ain't
going to work. Building on what Jeff Higgins wrote, here's a direct
link to an example which builds a very simple GUI on the EDT:
<http://download.oracle.com/docs/cd/E17409_01/javase/tutorial/deployment/applet/getStarted.html>
You should study that, the rest of the section there on "Applets", and
read through the Concurrency in Swing tutorial:
<http://download.oracle.com/docs/cd/E17409_01/javase/tutorial/uiswing/concurrency/index.html>
It's a pain in the rear but there isn't any other way. You're totally
stuck until you understand this stuff; we can't write ALL your code for
you. Once you get through with that, here's what I think a basic plan
would be:
1. Construct the first part of your GUI on the EDT as shown in the
example, up to where you append "Begin Counting" to the text area.
2. Find the "long task" part of your GUI; in your example it's that
while loop. That needs to be done OFF the GUI thread or it's going to
block all updates, including displaying the part of the GUI you just
made in #1.
3. Then, when #2 is done, display your final update(s) on the EDT.
Use a SwingWorker for the long task, it's the easiest way. It'll
execute long tasks "in the background" more or less automatically for
you, then run a foreground process on the EDT when it's done. Something
like:
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
public class MyWorker extends SwingWorker {
JTextArea textArea;
int ctr;
@Override
protected Object doInBackground()
throws Exception
{
// your long task here
while( ++ctr < 1000000 );
return null;
}
@Override
protected void done() {
textArea.append( "End counting " + ctr +" \n" );
}
}
That should give you enough to get something done on your own, although
you've got a fair amount of reading to do. Once you get that done and
write the improved version of you code, let us know how you are faring.
(I realize JTextArea.append() is thread safe, just in general you want
to know how to execute code on the EDT after completing some backgound
task.)