Re: GUI and events in text field

Nigel Wade <>
Fri, 09 Feb 2007 11:50:48 +0000
MikeB wrote:

On Feb 8, 4:29 pm, Knute Johnson <>

MikeB wrote:

Hi again, it has been a while since I posted here. I came here a while
back when I had a beginner's course in Java and again when I was
practicing my Java. I've finally managed to get into a more advanced
Java class and I need some guidance.

We have to create a GUI that validates some fields. For example, a
date field so that everything is numeric and within the right ranges
and so on. Can someone please write me one and send it to me?

Just Kidding!

Actually, I've written the first version of it, but it is not the way
I want it to be, hence my question.

I want to validate each field as the user finishes typing in that
field. If I understood the instructor correctly, that means I have to
monitor each keystroke in the field, but this sounds weird. I can see
how I can then interrupd and avoid text being entered into a nnumeric
field, but I think one should ony verify the field when the user tries
to leave it.

Now I think I can track that by checking if a field has focus or is
losing focus. Am I correct or is there a better way to track a field?

Is the event of losing focus something I implement in the
ActionListener? Or is it a specific event that I need to listen for?

Thanks for all advice.

Kind of depends if you are using AWT or Swing components. With AWT you
probably need to check each keystroke along with the finished field.
With Swing there are some neat classes like InputVerifier to keep you
from leaving a field and Document to limit the type of text data that is
entered into a field.


Knute Johnson
email s/nospam/knute/- Hide quoted text -

- Show quoted text -

Sorry, I should have specified. We're using NetBeans as IDE and are
developing in Swing. I'll look into the InputVerifier class. Thanks

There's a small section in the Swing Tutorial which explains input verification
using InputVerifier along with Focus events which might be of use to you:


I'm not sure whether a JFormattedTextField can be used to restrict the
characters which can be entered into it, but it might also be worth a look:


Nigel Wade, System Administrator, Space Plasma Physics Group,
            University of Leicester, Leicester, LE1 7RH, UK
E-mail :
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555

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