Java regex error - Look-behind group does not have an obvious maximum length

Asked 2011-09-25T04:59:03.713

I get this error:

java.util.regex.PatternSyntaxException: Look-behind group does not have an
    obvious maximum length near index 22
([a-z])(?!.*\1)(?<!\1.+)([a-z])(?!.*\2)(?<!\2.+)(.)(\3)(.)(\5)
                      ^

I'm trying to match COFFEE, but not BOBBEE.

I'm using java 1.6.

java regex lookbehind

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1 Answer

Java doesn't support variable length in look behind.
In this case, it seems you can easily ignore it (assuming your entire input is one word):

([a-z])(?!.*\1)([a-z])(?!.*\2)(.)(\3)(.)(\5)

Both lookbehinds do not add anything: the first asserts at least two characters where you only had one, and the second checks the second character is different from the first, which was already covered by (?!.*\1).

Working example: http://regexr.com?2up96

answered 2011-09-25T05:12:27.767

Java regex error - Look-behind group does not have an obvious maximum length

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