CODEWITHSUNDEEP
javaregex
Avi
Avi

Reputation: 2641

Java String replace - non-capturing group captures

I have the following Java code:

String initial = "Phone number: [194-582-9412]";
System.out.println(initial.replaceAll("\\d{3}\\-\\d{3}(?=\\-\\d{4})","XXX-XXX"));
System.out.println(initial.replaceAll("\\d{3}\\-\\d{3}(?:\\-\\d{4})","XXX-XXX"));

which produces output:

Phone number: [XXX-XXX-9412]
Phone number: [XXX-XXX]

My logic was to find 3 digits, a dash, 3 digits (capturing to this point), a dash, and four digits (non-capturing to this point). According to this tutorial, lookahead groups starting with ?= are non-capturing. According to the Pattern Javadoc, groups beginning with ?: are also non-capturing. I expected both regular expressions to produce the same output, Phone number: [XXX-XXX-9412]. However, the regular expression with the non-capturing group (?:\\-\\d{4}) seems to capture the entire phone number and replace it. Why is this happening?

Upvotes: 0

Views: 316

Answers (1)

WJS
WJS

Reputation: 40024

You can actually do what you wanted using capturing groups. Here it captures the part you want to keep and replaces the whole string. The $1 is a back reference to the capture group.

 System.out.println(
            initial.replaceAll("\\d{3}-\\d{3}(\\-\\d{4})", "XXX-XXX$1"));

And I presume you realize that if the regex doesn't match, then the original string is returned with no changes.

Upvotes: 1

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