Is Java RegExp group negation possible?

Question

I have the following regexp: (["'])(\\\1|[^\1])+\1

Obviously it could not be compiled because [^\1] is illeagal.

Is it possible to negate a matched group?

Answer 1

You can't use backreferences in a positive or negative character class.

But you can achieve what you want using negative lookahead assertions:

(["'])(?:\\.|(?!\1).)*\1

Explanation:

(["'])    # Match and remember a quote.
(?:       # Either match...
 \\.      # an escaped character
|         # or
 (?!\1)   # (unless that character is identical to the quote character in \1)
 .        # any character
)*        # any number of times.
\1        # Match the corresponding quote.