Here's the code I was using for my TextField:
form.add(new TextField("input_text", new PropertyModel(this, "inputText"), Integer.class)
If you type "-1" on the form, it gives you this error message:
'-1' is smaller than the minimum of 4.9E-324.
The work around to this is to use NumberValidator.minimum(0) instead. That, as far as I can tell, works the same way but gives this error message:
'-1' is smaller than the minimum of 0.
I think the user would prefer to see that.