A String method that checks to see the data is numeric?

**eLancaster** · 02-09-2011, 04:37 PM

I have a textfield in which the user is supposed to enter a number. I want to check to check the field to make sure the string contains only numbers. is there a function that can do that?

**Shoss** · 02-09-2011, 05:01 PM

The easiest way i can think of would be to use String's "matches" method. Then you can check the string against some regular expression to see if there are only digits. I'm not amazing with regex, but the bottom post here might be what you're looking for.

**quad64bit** · 02-09-2011, 05:04 PM

Yeah, simply try Long.parseLong() on the text they entered (you'll need a try catch). If an exception is thrown, then there was something other than a number and you can notify the user. If no exception is thrown, its a number. This will work on anything up to Long.MAX_VALUE.
If you're dealing with much larger numbers, then you might try using a simple regex inside the String.contains() method. You could search for non-number types like [a-zA-Z\s] and symbols. If a match is found, then there are non-numbers in the string. Good Luck!

**JosAH** · 02-09-2011, 05:16 PM

Originally Posted by quad64bit

Yeah, simply try Long.parseLong() on the text they entered (you'll need a try catch). If an exception is thrown, then there was something other than a number and you can notify the user. If no exception is thrown, its a number. This will work on anything up to Long.MAX_VALUE.

What if the user wants to enter a floating point number? Just accepting large integral numbers won't do it. My suggestion is to use a X.parseX() method for X == Integer, Double or Long; the op should make a choice.

kind regards,

Jos

**quad64bit** · 02-09-2011, 05:18 PM

Good point! I took the OP's

string contains only numbers

to mean a string with only digit characters.

**JosAH** · 02-09-2011, 05:38 PM

Originally Posted by quad64bit

Good point! I took the OP's to mean a string with only digit characters.

Mwah, the String "42.54" contains a number too. The OP should've been more explicit w.r.t. numbers/digits.

kind regards,

Jos

**eLancaster** · 02-09-2011, 07:26 PM

Thanks, I've got the answer I wanted and sorry for not being specific. the number had to be an int - no decimal points!
By the way, what does OP stand for?