Character class: union - Java regular expressions

The character classes in Java regular expression is defined using the square brackets "[ ]", this subexpression matches a single character from the specified or, set of possible characters. For example the regular expression [abc] matches a single character a or, b or, c.

The union variant of the character class allows you to match a character from one of the specified ranges i.e. the expression [a-z[0-9]] matches a single character which is either a small alphabet (a-z) or a digit (0-9).

Example

 Live Demo

import java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class RegexExample1 {    public static void main(String[] args) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");       String input = sc.nextLine();       String regex = "[a-z[0-9]]";       //Creating a pattern object       Pattern pattern = Pattern.compile(regex);       //Matching the compiled pattern in the String       Matcher matcher = pattern.matcher(input);       int count =0;       while (matcher.find()) {          count++;       }       System.out.println("Number characters from the ranges (a-z or 0-9): "+count);    } }

Output

Enter input text: sample DATA 12345 Number characters from the ranges (a-z or 0-9): 11