Building a GUI in Netbeans, which should I use? - user-interface

Question

I am building a GUI in Netbeans - it is for a simple little application - a converter program. Basically, user types whatever it is they want to convert into a text field, selects the conversion from a number of radio buttons (say lbs to kg) and then clicks "Convert".
The thing is, I want the "Convert" button and the radio buttons to behave like this:
Radio buttons and "Convert" button are disabled when program loads.
Radio buttons and "Convert" button will become enabled if user types a number (and only a number) into the text field.
If used deletes what they have typed, everything will be disabled again until they type in another number.
I have managed to set the Radio buttons and "Convert" button up so they are disabled, by unchecking the "enabled" box in the properties for each component. I have also been able to use a simple if statement and the keyTyped event to enable/disable as follows:
private void txtUsrInputKeyTyped(java.awt.event.KeyEvent evt)
{
if (!txtUsrInput.getText().equals(""))
{
btnCalculate.setEnabled(true);
}
else
{
btnCalculate.setEnabled(false);
}
}
I want to extend my code so that if the user accidentally types a letter or symbol into the text field (don't ask me why they'd do that, when they know they must only type a number) then the program will either ignore what they typed, or display an error. The exception to this is, of course, typing a period (.) because they might want to indicate a decimal number.
Any thoughts on how I might do this? Hope what I wrote makes sense!

Answer 1

Your GUI
If you do not already know swing, then learn it. Knowing how all of the components work is always a huge advantage for any developer, and if anything goes wrong, you know exactly how to fix it (or at least have a much better chance). Take a look at this stuff, for some help on getting started.
Checking for a decimal
This looks like a job for regular expressions. What you can do is specify a number [0-9], and a period, \.. Then ensure that either a number or a decimal is typed a certain amount of times. The important thing to note here though, is that the user can only type one decimal, which winds up being:
([0-9]+(\.[0-9]+))
This will allow values like 9, 0.9, 1.9302. It will not allow values like .901. If you wish to allow that, simple swap the first + for a *.:
([0-9]*(\.[0-9]+))
Using it
Because a text box contains a string, you can compare it with your regex. Simply:
if(textBox1.getText().matches("([0-9]+(\.[0-9]+))")) {
// Run some code in here.
}

Answer 2

Well, if GUI is simple, DO NOT use GUI Builder, but code from scratch. Following harder path, you will learn about layouts, actionlisteners and so on ...