Regular expression in java for validating numbers

By combining the expression for numbers and alphabetic characters, there is an expression that checks, whether the entered things includes numbers and alphabetic character or not.The expression for matching numbers and characters in the field is: /^[0-9a-z A-Z] $/ It’s must to provide validation in the select field.Example requirements are as follows.1) Username must be 8 to 20 characters in length 2) Username can only contain alphanumeric characters, numbers, underscore (_) and dot (.) 3) Username cannot start with underscore and dot Let’s try to build the regular expression pattern for the above requirements. The first username “john” and “Smith19” are not valid because they contain only 4 and 7 characters respectively.We want only alphanumeric characters so it should be a to z or A to Z. “James [email protected]” is not valid because it contains @ symbol which is not allowed.

escaping - by -) [0-9] : It matches digital number from 0-9. That means, you could be very sure about the form, whether users have entered the details or not.There may be different requirements to validate username.This example covers most common requirement of them. Here is the initial pattern as per the requirements.These usernames are valid as per our defined requirements but in real world they might not.

In short, underscore (_) and (.) cannot appear in sequence.

Validation codes will return an alert message, if it finds some empty fields in the form.

Regular expression in java for validating numbers comments

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