Understand java regex expressions

Question

"(?<=(.))(?!\\1)"

Can someone help me break this down?

I understand that ?<= is looking at all the characters following (.) basically any character, but then i get lost on the (?!\1) part.

Im very new to regex and while this has helped solve my problem i really want to understand whats going on here.

Thanks!

@schmosel didn't mean to, just a side-effect of code-formatting. That being said, OP did type 3 backslashes. Maybe it was intentional — Phil, May 31 '18 at 03:11
`?!` means negative lookahead, \\ is a escaped character and `1` matches 1 character — hatched, May 31 '18 at 03:24

score -1 · Answer 1 · answered May 31 '18 at 03:22

(.) matches any character and defines a capturing group.
(?<=(.)) is a positive lookbehind which matches any position preceded by some character.
\1 is a backreference to the previously captured character.
(?!\1) is a negative lookahead which matches a position not followed by the previous character.

In other words, find a position preceded by some character and not followed by the same character.

I'm guessing it's used to split a string into groups of repeating characters.

1 Answers1