The Java Developers Almanac 1.4

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e438. Using a Non-Capturing Group in a Regular Expression

By default, a group captures text (see e436 Capturing Text in a Group in a Regular Expression). In some cases, a group is needed but there is no need to capture the text. A non-capturing group should be used to improve performance. A non-capturing group starts with (?:.

    String inputStr = "abbabcd";
    String patternStr = "(a(?:b*))+(c*)";
    // (?:b*) is a non-capturing group
    
    // Compile and use regular expression
    Pattern pattern = Pattern.compile(patternStr);
    Matcher matcher = pattern.matcher(inputStr);
    boolean matchFound = matcher.find();
    
    if (matchFound) {
        // Get all groups for this match
        for (int i=0; i<=matcher.groupCount(); i++) {
            String groupStr = matcher.group(i);
        }
        // group 0: abbabc
        // group 1: ab
        // group 2: c
    }