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Java regular expression character class regex

Regular expressions

Regular expressions represents a sequence of symbols and characters expressing a string or pattern to be searched for within a longer piece of text. The abbreviation for regular expression is regex. In programming regular expressions are mainly used to define constraint on strings like password, email validation.

Java Regex Character classes

Character Class Description
[abc] a, b, or c (simple class)
[^abc] Any character except a, b, or c (negation)
[a-zA-Z] a through z or A through Z, inclusive (range)
[a-d[m-p]] a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]] d, e, or f (intersection)
[a-z&&[^bc]] a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]] a through z, and not m through p: [a-lq-z](subtraction)

Regex Character Class Example

package com.codesjava;
import java.util.regex.Pattern;
public class RegexTest {
	public static void main(String args[]){
		//true (2nd char is j)
		System.out.println(Pattern.matches(".j", "pj"));  
		//false (2nd char is not s)  
		System.out.println(Pattern.matches(".j", "ab"));
		//false (s is not the last char)  
		System.out.println(Pattern.matches(".s", "msa"));
		//false (has more than 2 char before s)  
		System.out.println(Pattern.matches(".s", "pjms"));
		//true (3rd char is s)   
		System.out.println(Pattern.matches("..s", "pjs"));


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