Check if a username is correct using Regex

Author: SedaKunda

Java/Strings/UserName.java

@@ -0,0 +1,40 @@
+/*
+Regular expressions (regexpregexp) help us match or search for patterns in strings. In this problem, you will be given a username. Your task is to check whether that username is valid. A valid username will have the following properties:
+1. The username can contain alphanumeric characters and/or underscores(_).
+2. The username must start with an alphabetic character.
+      8 ≤≤ |Username| ≤≤ 30.
+To simplify your task, we have provided a portion of the code in the editor. You just need to write down the regexregex pattern which will be used to validate the username input.
+
+Input Format
+The first line of input contains an integer NN, representing the number of testcases. Each of the next NN lines contains a string that represents a username.
+Constraints
+The username consists of any printable characters.
+    1≤N≤1001≤N≤100
+Output Format
+For each username, output Valid if the username is valid; otherwise, output Invalid.
+*/
+
+import java.io.*;
+import java.util.*;
+import java.text.*;
+import java.math.*;
+import java.util.regex.*;
+
+public class UserName {
+   public static void main(String[] args){
+      Scanner in = new Scanner(System.in);
+      int testCases = Integer.parseInt(in.nextLine());
+      while(testCases>0){
+         String username = in.nextLine();
+         String pattern = "^[a-zA-Z]{1,1}[a-zA-Z0-9_]{7,29}$";
+           Pattern r = Pattern.compile(pattern);
+           Matcher m = r.matcher(username);
+         if (m.find( )) {
+            System.out.println("Valid");
+         } else {
+            System.out.println("Invalid");
+         }
+         testCases--;
+      }
+   }
+}