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javaregexlookbehind

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

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.

Solution

  • 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