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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
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
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