Count the number of vowels in Java

Understanding Vowel Counting

Vowel counting involves determining the number of vowels (a, e, i, o, u) in a given string.

We will explore three different methods to count the vowels in a string using Java.

Method 1: Using a Loop

This method iterates through the string and counts each vowel.

import java.util.Scanner;

public class VowelCounter {
    public static int countVowels(String str) {
        int count = 0;
        str = str.toLowerCase();
        for (char ch : str.toCharArray()) {
            if ("aeiou".indexOf(ch) != -1) {
                count++;
            }
        }
        return count;
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String str = scanner.nextLine();
        System.out.println("Number of vowels: " + countVowels(str));
        scanner.close();
    }
}
            

Method 2: Using Recursion

This method counts vowels recursively.

import java.util.Scanner;

public class VowelCounterRecursive {
    public static int countVowelsRecursive(String str, int index) {
        if (index == str.length()) return 0;
        char ch = Character.toLowerCase(str.charAt(index));
        int count = ("aeiou".indexOf(ch) != -1) ? 1 : 0;
        return count + countVowelsRecursive(str, index + 1);
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String str = scanner.nextLine();
        System.out.println("Number of vowels: " + countVowelsRecursive(str, 0));
        scanner.close();
    }
}
            

Method 3: Using Streams

This method uses Java Streams to count vowels efficiently.

import java.util.Scanner;

public class VowelCounterStream {
    public static long countVowelsStream(String str) {
        return str.toLowerCase().chars()
                .filter(ch -> "aeiou".indexOf(ch) != -1)
                .count();
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String str = scanner.nextLine();
        System.out.println("Number of vowels: " + countVowelsStream(str));
        scanner.close();
    }
}