Regex in Java use same group in alternative matches

Question

I have a regex pattern which matches different expressions but i want both matches to be in the same capturing group. Currently i got the following regex:

-([^\s"]+)|-"(.+?)"

This does in fact match both (-hello -"Hello World") but in different groups (-hello = group1 and "Hello World" = group2).

In fact I got a working example, which is unfortunately not possible in Java regex:

(?|-([^\s"]+)|-"(.+?)")

Branch reset groups are not supported in Java regex. Use your regex, and some code to detect which group is not null. — Wiktor Stribiżew, Aug 26 '21 at 09:44

score 4 · Accepted Answer · edited Aug 26 '21 at 10:51

One option is to use look around assertion so you can get rid of all capture groups and get full match in result:

(?<=-)[^\s"]+|(?<=-")[^"]*(?=")

RegEx Demo

Pattern p = Pattern.compile("(?<=-)[^\\s\"]+|(?<=-\")[^\"]*(?=\")");

List<String> res = p.matcher("(-hello -\"Hello World\")")
        .results()
        .map(MatchResult::group)
        .collect(Collectors.toList());

//=> [hello, Hello World]

score 2 · Answer 2 · answered Aug 26 '21 at 09:50

Just use a regex pattern matcher and check both capture groups, using whichever one is not null:

String input = "-hello -\"Hello World\"";
String pattern = "-([^\\s\"]+)|-\"(.+?)\"";
Pattern r = Pattern.compile(pattern);
Matcher m = r.matcher(input);
while (m.find()) {
    String match = !Objects.isNull(m.group(1)) ? m.group(1) : m.group(2);
    System.out.println("Found a match: " + match);
}

This prints:

Found a match: hello
Found a match: Hello World

Regex in Java use same group in alternative matches

2 Answers2