Java Regex: How to match all patterns including overlapping regex matches?

Question

Suppose I have a String NNNN.

The regex is N+N.

How to configure the matcher to let it return NNNN, NNN and NN since NNN and NN also match pattern N+N?

You could find this yourself if you searched for overlapping regex matches. Nested is a bit different category. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 24, 2015 at 15:30
@stribizhev Thank you, I just don't know what's the jargon to describe my problem. — spacegoing
– spacegoing, Commented Aug 24, 2015 at 15:32

Casimir et Hippolyte · Accepted Answer · 2015-08-24 15:17:00Z

5

You need to enclose your pattern in a lookahead and a capture group:

(?=(N+N))

The results are in the group 1.

Since the lookahead is a zero-width assertion, characters are not consumed by the pattern and can be "reuse" for the next match (from the next position in the string).

N    N    N    N  
x______________^  # first match
     x_________^  # second match
          x____^  # third match

x____^ is the content of the capture group and x is the start position.

edited Aug 24, 2015 at 15:17

answered Aug 24, 2015 at 15:10

Casimir et Hippolyte

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2 Comments

spacegoing Over a year ago

Nice Answer! However, would you please tell me how could I find the start and end for each group in Java?

nhahtdh Over a year ago

@spacegoing: Matcher.start() and Matcher.end().

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