问题
I want to create a regex that allows only class names not ending with Impl. I'v read that "not ends with" could be tested with a negative lookahead (?!), but I cannot find a working (Java) regex.
I tried
[A-Z][A-Za-z\d]*?(?!Impl)
but it matches SomeImpl, what shouldn't be the case.
What regex wouldn't match class names ending with Impl?
回答1:
A negative lookahead wont work because - with the *? (lazy zero-or-more) quantifier - it'll check at S and find no Impl immediately ahead so the match succeeds.
If you changed to a greedy quantifier (change * to *?) it would still fail because you would be at the end of the string - there is no "ahead" to look at.
Instead you want to use a negative lookbehind to check the previous content, i.e.
[A-Z][A-Za-z\d]*(?<!Impl)
(You may or not want $ at the end of that, depending on where the pattern is used)
Side note: not directly relevant here, but useful to know is that (in Java regex) a lookbehind must have a limited width - you can't use * or + quantifiers, and must instead use limited numerical quantifiers, e.g. {0,99}
But unless the pattern itself is important (or you're working in a context where you must use regex), a simpler option would be String.endsWith, like so:
! mystring.endsWith('Impl')
来源：https://stackoverflow.com/questions/22964598/regex-not-matching-words-ending-with-impl