Naming a capturing group

We can assign a name to capturing group and use it in the Regular expression processing.

Naming Conventions

1. The first character must be a letter.

2. You can use uppercase letters 'A' through 'Z', lowercase letters 'a' through 'z' and digits '0' through '9'.

The newly added RegEx constructs to support the named capturing group are:

(1) (?<NAME>X) to define a named group NAME"

(2) \\k<Name> to backref a named group "NAME"

(3) <$<NAME> to reference to captured group in matcher's replacement str

(4) group(String NAME) to return the captured input subsequence by the given "named group"

import java.util.regex.*;
        
public class CaptureGroupEx {
    public static void main(String args[]){
        String name = "(?<number>\\d+)\\s\\k<number>";
        Matcher m = Pattern.compile(name).matcher("1234 1234");
        
        while (m.find()) {
            System.out.print("I found the text " + m.group());
            System.out.print(" starting at index " + m.start());
            System.out.println(" Ending at index " + m.end());
        }        
    }
}

Output

I found the text 1234 1234 starting at index 0 Ending at index 9

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