Eprogramy - Java: Regex Crash Course - The Ultimate Beginners Course to Learning Java Regular Expressions in Under 12 Hours

They are used for searching, editing and manipulating data. For example, using regular expressions we can verify if a particular input string matches a given text pattern or to find out a set of characters from a large batch of characters. They are also used in replacing and re-arranging a block of text or splitting a big chunk of data into smaller subsets. Regular expressions are generally not language specific and follow a similar pattern in most of the programming languages, but with slight variation. Regular expressions are powerful tools and would reduce the time taken for processing a job, when your program needs to manipulate or extract text on computer. By using them skillfully, regular expressions help us to perform many tasks that wouldnt be feasible at all.

Regular expressions are so useful in real life computing that, the various systems and languages have evolved to provide both a fundamental and protracted standard for the grammar and syntax for usage of modern regular expressions. Also Regular expression processors are found in major of the search engines, search and replace place-holders of various word processors and text editors, and in the command lines of utilities that re used in processing text inputs. Example: Lets assume we need to validate the following email. String emailid = . Steps required to validate: (For now are not interested in a valid email address but just the format) Just validate the format with @ symbol. There must be a character preceding and succeeding the @ symbol without space.

The text/ string preceding @ symbol must contain only characters, digit, underscores and hyphen. There should not be two @ symbols in the email address There should be a . in the domain name succeeding the @ symbol If you need to verify the above email id, without regular expressions, a program would need hundreds of lines of code for implementation. We can use the emailid.indexOf (@) from the String class for the first step of validation and then on keep adding lines of code for the rest of the steps resulting in a tedious job of coding as well as maintenance would be a nightmare after that. package com.sample.regexsample; public class ValidteEmail { public static void main(String[] args ) { String str1 = "myname@abc.com" ; int x = str1 .indexOf( "@" ); // returns index of first character of the substring "tutorials" System. out .println( "index = " + x ); } } Output: Index = 6.

Once after obtaining the index, further calculations are required to find out if it is there are one to many characters in the domain name, followed by a . Symbol and it end with 2 or 3 characters. This is where regular expression plays an important role .We can accomplish it in just one line of code using the regex patterns. ( Well see the example codes in the coming chapters) package com.sample.regexsample; import java.util.regex.Matcher; import java.util.regex.Pattern; public class EmailValidator { public static void main(String[] args ) { String input = "^[_A-Za-z0-9-\\+]+( " ; Regex For email lets discuss more on this in further chapters Now we need to understand Regex simplifies the process. String emailAddress = "xyz@abc.com" ; Pattern p = Pattern. out .println ( "The email 1 matches:" + m .matches()); } }