Regular Expressions

Introduction

Regular expressions in Java are useful for searching, editing and manipulating strings. Regular Expressions are also known as Regex.

Java Regex provides three classes in java.util.regex package:

• Matcher
  — Used for defining the String pattern to match
• Pattern
  — Used for peforning math on given pattern
• PatternSyntaxException
  — Used for indicate exceptions in the pattern

RegEx Example:

• Check that the string contains only characters and no numbers or special characters.

import java.util.regex.*; 

public class RegExExample {
    public static final String ARTICLE_STRING = "Codevarsity";

    public static void main(String[] args) {
        Pattern pattern = Pattern.compile("^[a-zA-Z]*$");  
        Matcher match = pattern.matcher(ARTICLE_STRING);  
        boolean result = match.matches();  
        System.out.println("Result: " + result);
    }
}

Result: true

Understanding the pattern:

"^[a-zA-Z]*$"

^ – The beginning of a line
[a-zA-Z] – Match characters from a-z and A-Z
*$ – The end of the line

RegEx Cheatsheet:

• Here is a very good link to RegEx Cheatsheet

More Information:

• Class Pattern
• Lesson on Regular Expression