Java specific regex

Question

I want to write some code that checks whether the input from user matches a specific format. The format is 's' followed by a space and a number, if the input was "s 1 2 3 4", it would call some function. "s 1 2" would also be acceptable. So far I found that this regex works for a specified amount of times:

if (inputLine.matches("s \\d+ \\d+")) { }

works for 2 numbers after the s, but I need to be able to accept any number of numbers after the s. Any idea on a regex that would suit my needs? Thank you

Try this. "s( \\d+)+" There is a space after the opening bracket — denvercoder9, Dec 07 '16 at 23:07

Wiktor Stribiżew · Answer 1 · 2016-12-07T23:09:23.327

4

Change your regex to

if (inputLine.matches("s(?: \\d+)+")) { }

to match s, space and 1+ sequences of a space followed with 1+ digits.

If you allow 0 numbers after s, replace the last + quantifier with * to match zero or more occurrences.

Since the repeated capturing groups overwrite the group contents, it makes no sense using a capturing group here, thus, I suggest using a non-capturing one, (?:...).

edited Dec 07 '16 at 23:09

answered Dec 07 '16 at 23:07

Wiktor Stribiżew

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Man, you are always so fast with these regex questions! – denvercoder9 Dec 07 '16 at 23:08
@RafiduzzamanSonnet: I learnt that from [@AvinashRaj](http://stackoverflow.com/users/3297613/avinash-raj). – Wiktor Stribiżew Dec 07 '16 at 23:10
Most of the answer I see from you has "(?:" of some sort. I thought "?" means "zero" or "one". Can you point me to a good resource on this? :) – denvercoder9 Dec 07 '16 at 23:11
2

@RafiduzzamanSonnet: Perhaps, [What is a non-capturing group? What does a question mark followed by a colon (?:) mean?](http://stackoverflow.com/questions/3512471/what-is-a-non-capturing-group-what-does-a-question-mark-followed-by-a-colon) can throw some light on it. – Wiktor Stribiżew Dec 07 '16 at 23:12
Thanks a lot for the link! – denvercoder9 Dec 07 '16 at 23:16

Java specific regex

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