CODEWITHSUNDEEP
javaregex
Chirag
Chirag

Reputation: 13

Repetitive numbers not matched by RegEx

I am using RegEx in Java to classify phone numbers and I am stuck finding consecutive repeating numbers.

Why is this RegEx

9{4}([0-8]\1{2})([0-9]\1{3})[0-9]

Not matching this string

9999227771

Upvotes: 1

Views: 80

Answers (1)

Tushar
Tushar

Reputation: 87203

In the regex

9{4}([0-8]\1{2})([0-9]\1{3})[0-9]

([0-8]\1{2}) This is first capturing group and inside that \1 - back-reference refers to itself which will not work.

In the second captured group ([0-9]\1{3}), you are again referring to first captured group.

Also, both the back-references are repeated n times which should be n-1 as first number is matched by the capturing group.

Here is corrected regex

9{4}([0-8])\1([0-9])\2{2}[0-9]

RegEx101 Demo

  1. 9{4}: Repeat 9 four times. i.e. 9999
  2. ([0-8])\1: Match a number in the given range and match the same number again, thus \1.
  3. ([0-9])\2{2}: Match a digit and follow it by same digit twice

Note: To match exact phone numbers, use anchors ^ and $.

Upvotes: 2

Related Questions