Regular expression in java for validating numbers

13-Jun-2020 22:09 by 5 Comments

Regular expression in java for validating numbers - sex dating in phillips nebraska

Regular expressions are a good way to validate text fields such as names, addresses, phone numbers, and other user information. A regular expression can easily check whether a user entered something that looks like a valid phone number.

While regular expressions were supported by many UNIX tools for decades, it was only in the last decade or so that they have found their way into most Windows developers' toolkits.

These usernames are valid as per our defined requirements but in real world they might not.

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

Validating a username is a very common requirement while designing and developing web application.

This example will show you how to validate a username using Java regular expression.

Eventually, Ken Thompson built support for regular expressions into qed and grep, both very popular text utilities.

Jeffrey Friedl goes into more depth in his book, Mastering Regular Expressions (2 edition), which is strongly recommended for those wishing to learn more about the theory and history behind regular expressions.

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.

Every other usernames from above example are valid as per the pattern.

The last user name “_michael_clarke” is invalid as per our requirement but it turns out be valid as per our pattern.

There may be different requirements to validate username.

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