Java Regex Non-Capturing Group

Question

I am having some trouble getting regex to match a string in Java. Here are the strings I want to match: String Transformation Action and Transformation Action. Basically, if String is present, I want to match it, otherwise I would only match the remaining String.

I tried to utilize non-capturing group in regex, however it is not working.

Here is my regex: String regexFilter = "(?:String) (Transformation) (Action)";. This will match String Transformation Action, however as soon as I take away String, it will not match.

Read about quantifiers.

Seelenvirtuose
– Seelenvirtuose

2014-06-26 14:21:56 +00:00
Commented Jun 26, 2014 at 14:21 — Seelenvirtuose
– Seelenvirtuose, Commented Jun 26, 2014 at 14:21

arshajii · Accepted Answer · 2014-06-26 14:20:12Z

2

You need to make the String part optional by using a ?:

String regexFilter = "(?:String )?(Transformation) (Action)";

Also, there isn't much point in putting capturing groups around literal text (e.g. Transformation and Action) since you always know what those groups will capture.

String regexFilter = "(?:String )?Transformation Action";

answered Jun 26, 2014 at 14:20

arshajii

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3 Comments

mrQWERTY Over a year ago

What if I also want "Action" to be optional too? I tried the same with "Action" and it did not work as well as "String".

arshajii Over a year ago

@Froggy Did you try (?:String )?Transformation(?: Action)??

mrQWERTY Over a year ago

Ah, I see. I did that except I did put a space between "Transformation" and "Action" group.

anubhava · Accepted Answer · 2014-06-26 14:20:46Z

1

Make String part optional using this regex:

String regexFilter = "\\b(?:String )?Transformation Action\\b";

PS: I have also added \\b (word boundary) to make your don't match Transformation Action111 OR xyzTransformation Action type strings.

answered Jun 26, 2014 at 14:20

anubhava

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Comments

hwnd · Accepted Answer · 2014-06-26 14:29:11Z

1

You need to make the non-capturing group optional. The ? quantifier means match (1 or 0 times)

String regexFilter = "(?:String )?(Transformation) (Action)";

edited Jun 26, 2014 at 14:29

answered Jun 26, 2014 at 14:21

hwnd

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