String with N digits

Question

I need some help with regex in Java.

We have string, and I want that String.matches give me "true" if our string contains N digits.

For example( N = 12 ):

+012345678900 - true

0123-4567-0000 - true;

but:

+0123456789 - false

0123-4567-000000 - false.

I tried this one (.*[0-9].*){N} and this one ^(.*[0-9].*){N}$ . But it was incorrectly.

Answer 1

You may try this,

^(?:\\D*\\d){12}\\D*$

matches method won't need anchors, so

(?:\\D*\\d){12}\\D*

would be enough..

\\\\D matches any character but not of digit. So (?:\\\\D*\\\\d){12} ensures that there must be any no of non-dgit chars but it must contain exactly 12 digits. Last \\\\D* matches zero or more non-digit characters.