How does back reference to a matching group inside the group itself work in regex?

Asked Sep 20 '18 at 17:13

Active Sep 20 '18 at 18:19

Viewed 53 times

I am trying to understand a regex in Java that finds if a string of ANY length is a palindrome or not, as below:

\A(?:(.)(?=.*?(\1\2?)\z))*?.?\2\z

It matches a palindrome of all lengths. Can someone explain how is it exactly working? Specifically this part:

(?=.*?(\1\2?)\z))

wherein the second capturing group(\1\2?) is back-referenced within itself(\2)?

edited Sep 20 '18 at 17:14

asked Sep 20 '18 at 17:13

ashwani kumar

@WiktorStribiżew IMO it's valid and interesitng question. And it is definitely NOT duplicate of what you posted and doesn't qualify as question mentioned there. – Michał Turczyn Sep 20 '18 at 17:45
1

This regex doesn't seem right. It also accepts `aaba`. – Pshemo Sep 20 '18 at 18:10

0 Answers0