Re: setText() is not always updating Jtextfield and Jlabel items

Knute Johnson <>
Thu, 26 Feb 2015 20:05:35 -0800
On 2/26/2015 12:23 PM, Kevin Nathan wrote:

I could use some direction about where to look for this. I am still
pretty new to Java. I have a user input screen with multiple
JTextFields for user input and matching JLabels for informational
output for users.

This is for a livestock auction system. While the animals are moving
around on the scale, the scale instrument (a serial port device)
returns an indication of "motion" that we want to show to the user.
When the motion goes away, the actual weight gets written to the Weight
JTextField. However, during the motion (which can be anywhere from
non-existent to many seconds) we want to write "Motion" in the
textfield and the actual, changing, weights in the label field. This is
what is not happening. After the motion stops, the true weight does get
written correctly, using setText().

The serial port routine returns an error code of -2 if there is motion
(and several other error codes that are handled correctly) and that is
what I am using. Here are some code snippets to show what is being
attempted, I hope it's enough to make sense:

MainScreen class:

// Trying new "Motion" routine:
while (clerkFuncs.scaleErr == -2) {
     weight = clerkFuncs.readScale(tr);

private void showMotion(long wt) {

     // noteField[1][weightRow].setText("<html><font


ClerkFuncs class:

// weight and weightStr are global in ClerkFuncs. I don't like it
// but that's how it was written.

public long readScale(TransClass tr) {
     clearScaleReturns(); // clears weight string and error var

     if (!scale.scalePortErr) {
     } else { // manual weight entry
     return (weight);

private void getAutoWeight() {

     do {
         weightStr = scale.getWeight();
     } while (scale.getStatus() && weightStr.equals(""));


private void checkForWeightErrors() {
     scaleErr = scale.scaleErr;
     try {
         String trimmed = weightStr.trim();
         if (!trimmed.isEmpty()) {
             weight = Long.parseLong(trimmed);
         } else {
             weight = 0L;
     } catch (NumberFormatException ex) {
         System.out.println("checkForWeightErrors Exception: " + ex);
         System.out.println("weightStr: [" + weightStr + "]");
         scaleErr = -3; // bad scale return
         weight = 0L;

I am completely puzzled why "setText" does not work in this instance,
but works everywhere else I am using it. Thanks for any help, or
pointers to pages that may help me to understand this

Two suggestions, first a call to JTextField.setText() must be on the
Event Dispatch Thread. I don't see you wrapping your calls on the EDT.

Second, if the GUI isn't updating it is probably because the updates are
not on the EDT or the EDT is blocked for some reason. Without more
coherent code it is difficult to tell what is going on.

But that is where I would look.


Knute Johnson

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