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Regular Expressions

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 = "freecodecamp";

    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

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