JAVA EE: How to capturing the groups with back reference in Regex | Java Regex

Friday 5 January 2018

How to capturing the groups with back reference in Regex | Java Regex | Regex in java

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RegexDemo.java

import java.util.regex.Matcher;

import java.util.regex.Pattern;

/**

 * 

 * Capturing Groups

 *

 */

public class RegexDemo

{

    public static void main(String[] args)

    {

        /*

         * Where there are two separate matches for the input, we can

         * have one match but propagating the same regex match to span

         * the entire length of the input using back referencing:

         */

        isMatch("(\\d\\d)\\1", "3434");

        isMatch("(\\d\\d)\\1", "3499");

        isMatch("(\\d\\d)\\1\\1", "343434");

        isMatch("(\\d\\d)\\1\\1", "343439");

    }

    private static void isMa
tch(String regex, String inputText)

    {

        Pattern pattern = Pattern.compile(regex);

        Matcher matcher = pattern.matcher(inputText);

        System.out.println("Regex = " + regex + " , " + "InputText = "

                + inputText + " is matching? = " + matcher.matches());

    }

}

Output

Regex = (\d\d)\1 , InputText = 3434 is matching? = true

Regex = (\d\d)\1 , InputText = 3499 is matching? = false

Regex = (\d\d)\1\1 , InputText = 343434 is matching? = true

Regex = (\d\d)\1\1 , InputText = 343439 is matching? = false