23. Valid Username Regular Expression - Java | Strings | Hackerrank

You are updating the username policy on your company's internal networking platform. According to the policy, a username is considered valid if all the following constraints are satisfied:

The username consists of 8 to 30 characters inclusive. If the username consists of less than 30 or greater than 8 characters, then it is an invalid username.
The username can only contain alphanumeric characters and underscores (_). Alphanumeric characters describe the character set consisting of lowercase characters , uppercase characters , and digits .
The first character of the username must be an alphabetic character, i.e., either lowercase character or uppercase character .

[shraddhakshirsagar]

But how can we come to know that why and where we have to use regular expression?

[rubenalbertassi]

Muito bom, estou com uma duvida quando se uma vírgula, se eu tiver um valor com, (vírgula) exemplo 124, 56 como ficaria?

[avijitdey]

^[a-zA-Z]\\w_{7, 29}$ why this not getting accepted?

[anujjain]

$ give error
I performed exactly as same ur code.

[sourabhtripathi]

no need to use ^ and $ at start and end