Java-Backreferences

Backreferences

The section of the input string matching the capturing group(s) is saved in memory for later recall via backreference. A backreference is specified in the regular expression as a backslash (\) followed by a digit indicating the number of the group to be recalled. For example, the expression (XX) defines one capturing group matching two XX in a row, which can be recalled later in the expression via the backreference \1.

Program

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Javaapp {
  
    public static void main(String[] args) {
        
        Pattern pat = Pattern.compile("(XX)(YY)\\d{4}\\2\\1");
        Matcher mat = pat.matcher("XXYY1234YYXX1234");
        
        int i = 0;
        while(mat.find())
        { 
            i++;
            System.out.println(i+"th subsequence  : "+mat.group());
        }
    }
}