Validating Username Using REGEX.

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Hello Everyone!πŸ’œ

Regex is one of the topics where almost every developer takes time in the beginning. So, let's practice it today by creating the regex pattern to validate a username. Let's begin!πŸš€

Before solving, if you are not aware of syntax for writing regular expressions do check it here!

I have taken this question from Hackerrank. Let's solve it.πŸ’ͺ


I recommend you to try before seeing the solution.


  1. First let's take username as input
    Scanner sc = new Scanner(;
    String userName = sc.nextLine();
  2. Creating a regex pattern for username validation.
String regularExpression= "^[A-Za-z][A-Za-z0-9_]{7,29}$";
  • A valid username should start with an alphabet so, [A-Za-z].
  • All other characters can be alphabets, numbers or an underscore so, [A-Za-z0-9_].
  • Since length constraint was given as 8-30 and we had already fixed the first character, so we give {7,29}.
  • We use ^ and $ to specify the beginning and end of matching.

3.Now, to check the username against the regular expression.

if (userName.matches(regularExpression)) {
    } else {

Final Code

import java.util.regex;
import java.util.Scanner;
public class Solution {

    public static void main(String[] args){
     Scanner sc = new Scanner(;
     String userName = sc.nextLine();
     String regularExpression = "^[A-Za-z][A-Za-z0-9_]{7,29}$";
     if (userName.matches(regularExpression)) {
    } else {


Hurray! We have successfully learnt validating username using regex in java today.😍

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DesignerAnna1's photo

Revision Done. πŸ‘ Screenshot 2020-11-29 at 6.13.47 AM.jpg

Varun Sridharan's photo

Nice Article.

It would be better if you could add the programing language in the title

Example : "Validating Username Using REGEX in Java."

Sai Laasya Vabilisetty's photo

Thank you! Will keep this in mind.

Aditya Chaudhary's photo


Sai Laasya Vabilisetty's photo

Thank You, Aditya!