Regular expression with repeating groups in Java Pattern

Question

Lets say I have the following strings:

mya!phaNum3rics-456-456-lll
zzzz-6a6-6a6-lll
vvvv-4-4-lll

These are considered matches because "second" and "third" group repeat, and last group ends with lll. What regex would allows for any character sequence in the second and third "group".

How much different if the following is also considered a match?

zasdfdf-zadezz-6a6-6a6-lll

"third to last group" repeats with "second to last group" and ends with "group" lll.

You are looking for backreferences: docs.oracle.com/javase/tutorial/essential/regex/…. — Pshemo
– Pshemo, Commented Oct 19, 2016 at 18:24
Yes, I will try backreferences. Never new this existed, especially within Java regex engine. — paulj
– paulj, Commented Oct 19, 2016 at 20:48

Wiktor Stribiżew · Accepted Answer · 2016-10-20 16:57:10Z

1

You need

-([^-]+)-\1-lll$

See the regex demo

- - a hyphen
([^-]+) - Group 1 capturing one or more symbols other than -
- - a hyphen
\1 - a backreference to the text captured into Group 1
-lll - a substring of literal characters
$ - end of string.

Java demo:

String str = "mya!phaNum3rics-456-456-lll";
Pattern ptrn = Pattern.compile("-([^-]+)-\\1-lll$");
Matcher matcher = ptrn.matcher(str);
if (matcher.find()) {
    System.out.println(matcher.group(0) + " matched!");
}

A variation of the same regex for use with .matches:

if (str.matches(".*-([^-]+)-\\1-lll")) {
    System.out.println(str + " matched!");
}

edited Oct 20, 2016 at 16:57

answered Oct 20, 2016 at 16:51

Wiktor Stribiżew

631k41 gold badges502 silver badges632 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Regular expression with repeating groups in Java Pattern

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related