Re: Coordinating multiple JTextField updates across panels

Knute Johnson <>
Mon, 15 Jun 2009 17:55:30 -0700
Jarrick Chagma wrote:

"Knute Johnson" <> wrote in message

Jarrick Chagma wrote:

"John B. Matthews" <nospam@nospam.invalid> wrote in message

In article
"Jarrick Chagma" <> wrote:

I have a large number of text fields in a number of JPanel panels
visible on
the screen at the same time and I would like to somehow coordinate
updating. A button click can trigger an event which updates every
one of
the text fields at the same time but there is a noticeable effect
of one
field updating after the next one (and not necessarily in any
order) which is visually unattractive and undesirable. I would
prefer that
the screen as a whole does not update until all the text field's
have changed. I can't do double-buffering in this scenario as the
are in different panels.

Perhaps you can arrange for your model to accumulate its results then
notify your view to update the display, _en_bloc_. The Observer pattern
works well in this case:


That's precisely what I am doing but no matter how much you do
something _en_bloc_ there still has to be a sequence of views that
are updated and it is this one-after-the-other sequence that causes
the visual problem. I try to put as little delay between each
sequential update as possible but even when they are on the next line
of code there is still a small (but perceptible) delay between each
update because they are in separate panels. When there are many views
on the screen this doesn't look too nice.

Is there a way to somehow coordinate these updates perhaps by
turning off
screen redraw until all fields in all panels have updated?

I don't know of such a way.

Yes, I figured as much but maybe someone can suggest a way?

Capture what's on the JPanel, draw that into the glass pane, update
your text fields and then clear the glass pane.

I'm afraid I don't quite follow you Knute. Could you explain in a bit
more detail? When you refer to the "glass pane", is that the glass pane
of the surrounding frame? How do I capture what's on a JPanel? Do you
realise that there are many, many panels and that this is the cause of
the problem?

This is slapped together and could have some threading issues but it
works to demonstrate the point.

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

public class test extends JPanel implements Runnable {
     JTextField[] fields = new JTextField[1200];
     int n;
     Robot robot;
     BufferedImage bi;
     MyGlassPane mgp;

     public test() throws AWTException {
         setLayout(new GridLayout(30,40));

         for (int i=0; i<fields.length; i++) {
             fields[i] = new JTextField("000");

         robot = new Robot();
         mgp = new MyGlassPane();

     public void run() {
         while (true) {
             Point p = getLocationOnScreen();
             Rectangle r = new Rectangle(p.x,p.y,getWidth(),getHeight());
             bi = robot.createScreenCapture(r);

             for (int i=0; i<fields.length; i++)


             try {
             } catch (InterruptedException ie) {

     class MyGlassPane extends JComponent {
         public void paintComponent(Graphics g) {

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 try {
                     JFrame f = new JFrame();
                     test t = new test();
                     new Thread(t).start();
                 } catch (AWTException awte) {


Knute Johnson
email s/nospam/knute2009/

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