Importance of java.util.regex

java.util.regex is a Java package used to work with Regular Expressions (Regex). It helps match, search, validate, and manipulate text using patterns. It is commonly used for validating emails, phone numbers, passwords, and other inputs. The main classes are Pattern and Matcher.

• Pattern matching – Checks whether text follows a pattern.
• Validation – Validates user input.
• Searching – Finds patterns inside text.
• Replacement – Replaces matching text.
• Extraction – Extracts required text.

Syntax:
Pattern pattern = Pattern.compile("regex");
Matcher matcher = pattern.matcher("input");
boolean result = matcher.matches();Code language: JavaScript (javascript)

Example: Match only digits
Pattern pattern = Pattern.compile("[0-9]+");
Matcher matcher = pattern.matcher("12345");
System.out.println(matcher.matches());Code language: JavaScript (javascript)

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class RegexDemo {
    public static void main(String[] args) {

        String input = "12345";

        Pattern pattern = Pattern.compile("[0-9]+");

        Matcher matcher = pattern.matcher(input);

        if (matcher.matches()) {
            System.out.println("Valid number");
        } else {
            System.out.println("Invalid number");
        }
    }
}

Output:
Valid number