Example: Count Vowels and Consonants - Regular Expressions in Java

// Count Vowels and Consonants - Regular Expressions
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        // Step 1: Initialize Scanner and get input string
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String inputString = scanner.nextLine();
        scanner.close();

        // Step 2: Convert the string to lowercase to simplify regex patterns
        String lowerCaseString = inputString.toLowerCase();

        // Step 3: Define regex patterns for vowels and consonants
        // [aeiou] matches any vowel
        Pattern vowelPattern = Pattern.compile("[aeiou]");
        // [a-z&&[^aeiou]] matches any lowercase letter that is not a vowel
        Pattern consonantPattern = Pattern.compile("[a-z&&[^aeiou]]");

        // Step 4: Count vowels
        Matcher vowelMatcher = vowelPattern.matcher(lowerCaseString);
        int vowelCount = 0;
        while (vowelMatcher.find()) {
            vowelCount++;
        }

        // Step 5: Count consonants
        Matcher consonantMatcher = consonantPattern.matcher(lowerCaseString);
        int consonantCount = 0;
        while (consonantMatcher.find()) {
            consonantCount++;
        }

        // Step 6: Print the results
        System.out.println("Vowels: " + vowelCount);
        System.out.println("Consonants: " + consonantCount);
    }
}