Question

JAVA Q

The criteria for a valid simple username is as follows:

• It should start with an English alphabet followed by alphanumeric characters.
• No special characters allowed
• Username length should be at least 3 and should not exceed 20.

You are required to complete the regular expression only. Your answer will be tested automatically.

For example: the following are valid username:

• abc001
• davidsmith

And the following are invalid username:

• 12helloworld"
• 336.12.1.2

Test	Result
isUsername("abc001"); isUsername("128.1.1");	abc001: matches 128.1.1: does not match

public static void isUsername(String inputStr) {
String regExpStr = ""; //complete this
Pattern pattern = Pattern.compile(regExpStr);
Matcher matcher = pattern.matcher(inputStr);
System.out.printf("%s\n", matcher.matches()? inputStr + ": matches": inputStr + ": does not match");
}

Answer 1

Java code

============================================================================================

import java.util.regex.*;

public class UserNameValidation {

   public static void isUsername(String inputStr) {
       String regExpStr = "^[a-zA-Z][a-zA-Z0-9]{3,20}$"; //complete this
       Pattern pattern = Pattern.compile(regExpStr);
       Matcher matcher = pattern.matcher(inputStr);
       System.out.printf("%s\n", matcher.matches()? inputStr + ": matches": inputStr + ": does not match");
       }
  
   public static void main(String[] args) {
       // TODO Auto-generated method stub
       isUsername("abc001");
       isUsername("128.1.1");
       isUsername("128aa");
       isUsername("aa");
   }

}

============================================================================================

Output