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
– denvercoder9, Commented Dec 7, 2016 at 23:07

Wiktor Stribiżew · Accepted Answer · 2016-12-07 23:09:23Z

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 7, 2016 at 23:09

answered Dec 7, 2016 at 23:07

Wiktor Stribiżew

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1 Comment

Wiktor Stribiżew Over a year ago

Perhaps, What is a non-capturing group? What does a question mark followed by a colon (?:) mean? can throw some light on it.

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