Java - regex for ordinary positive negative number

Question

I read a lot of regex question, but I didn't find this yet..

I want a regex in Java to check whether a string (no limit to length) is a number:

This is what I have done so far:

^(?-)[1-9]+[0-9]*

Please show us what you've got so far, and we'll help you along. — NPE
– NPE, Commented Dec 13, 2016 at 18:40
sorry, by "exclude +" do you mean 1) do not consider this a legitimate number, that is, +4 is NOT a number; or 2) do not include the + symbol in the resulting value, that is, +4 is really the number 4? only the first option makes any sense with the 0.5 example, but it seems odd that these legitimate numbers are being excluded. do you really mean, determine if the number is an integer? careful with the terminology, all of those examples are indeed numbers... — ryonts
– ryonts, Commented Dec 13, 2016 at 18:53
@ryonts excluding the sign +. which make the number +4 illegal:) — J. Doe
– J. Doe, Commented Dec 13, 2016 at 18:56

fabian · Accepted Answer · 2016-12-13 18:49:49Z

13

The is a optional -

-?

The number must not start with a 0

[1-9]

it may be followed by an arbitraty number of digits

\d*

0 is an exception to the "does not start with 0 rule", therefore you can add 0 as alternative.

Final regex

-?[1-9]\d*|0

java code

String input = ...

boolean number = input.matches("-?[1-9]\\d*|0");

answered Dec 13, 2016 at 18:49

fabian

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