Java: Count all vowels in a string

Java Method: Exercise-4 with Solution

Count Vowels in String

Write a Java method to count all vowels in a string.

Sample Solution:

Test Data:
Input the string: w3resource

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.Scanner;
public class Exercise4 {
  public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        System.out.print("Input the string: ");
        String str = in.nextLine();

        System.out.print("Number of  Vowels in the string: " + count_Vowels(str)+"\n");
    }
 public static int count_Vowels(String str)
    {
        int count = 0;
        for (int i = 0; i < str.length(); i++)
        {
            if (str.charAt(i) == 'a' || str.charAt(i) == 'e' || str.charAt(i) == 'i'
                    || str.charAt(i) == 'o' || str.charAt(i) == 'u')
            {
                count++;
            }
        }
        return count;
    }
}

Sample Output:

Input the string: w3resource                                                                                  
Number of  Vowels in the string: 4

Flowchart:

Count the Vowels And Consonants in a string

Main.java Code:

//MIT License: https://bit.ly/35gZLa3
import java.util.concurrent.TimeUnit;

public class Main {

    // 14 vowels, 19 consonants
    private static final String TEXT = " ... Illinois Mathematics & Science Academy ... ";            
    
    public static void main(String[] args) {
        
        System.out.println("Input text: \n" + TEXT + "\n");
        
        System.out.println("String.charAt() solution:");
        long startTimeV1 = System.nanoTime();
        
        Pair pairV1 = Strings.countVowelsAndConsonantsV1(TEXT);        
        
        displayExecutionTime(System.nanoTime() - startTimeV1);
        System.out.println("Vowels: " + pairV1.vowels);
        System.out.println("Consonants: " + pairV1.consonants);
        
        System.out.println();        
        System.out.println("Java 8, functional-style solution:");
        long startTimeV2 = System.nanoTime();
        
        Pair pairV2 = Strings.countVowelsAndConsonantsV2(TEXT);        
        
        displayExecutionTime(System.nanoTime() - startTimeV2);
        System.out.println("Vowels: " + pairV2.vowels);
        System.out.println("Consonants: " + pairV2.consonants);        
    }

    private static void displayExecutionTime(long time) {
        System.out.println("Execution time: " + time + " ns" + " ("
                + TimeUnit.MILLISECONDS.convert(time, TimeUnit.NANOSECONDS) + " ms)");
    }
}

Pair.java Code:

//MIT License: https://bit.ly/35gZLa3
public final class Pair<V, C> {

    final V vowels;
    final C consonants;

    public Pair(V vowels, C consonants) {
        this.vowels = vowels;
        this.consonants = consonants;
    }

    static <V, C> Pair<V, C> of(V vowels, C consonants) {
        return new Pair<>(vowels, consonants);
    }

    @Override
    public int hashCode() {
        return vowels.hashCode() ^ consonants.hashCode();
    }

    @Override
    public boolean equals(Object o) {
        if (!(o instanceof Pair)) {
            return false;
        }
        
        Pair obj = (Pair) o;
        return this.vowels.equals(obj.vowels)
                && this.consonants.equals(obj.consonants);
    }
}

Strings.java Code:

//MIT License: https://bit.ly/35gZLa3
import java.util.Arrays;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.partitioningBy;

public final class Strings {

    private static final Set<Character> allVowels
            = new HashSet(Arrays.asList('a', 'e', 'i', 'o', 'u'));

    private Strings() {
        throw new AssertionError("Cannot be instantiated");
    }

    // Note: For Unicode supplementary characters use codePointAt() instead of charAt()
    //       and codePoints() instead of chars()
    //       Also, note that languages can have a different number of vowels and consonants
    //       (e.g., in Romanian there are 7 vowels: a, e, i, o, u, ă, î (â). Therefore, 
    //       consider adjust the code accordingly.
    public static Pair<Integer, Integer> countVowelsAndConsonantsV1(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return Pair.of(-1, -1);
        }

        str = str.toLowerCase();

        int vowels = 0;
        int consonants = 0;
        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);
            if (allVowels.contains(ch)) {
                vowels++;
            } else if ((ch >= 'a' && ch <= 'z')) {
                consonants++;
            }
        }

        return Pair.of(vowels, consonants);
    }

    public static Pair<Long, Long> countVowelsAndConsonantsV2(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return Pair.of(-1L, -1L);
        }

        str = str.toLowerCase();

        /*
        long vowels = str.chars()
                .filter(c -> allVowels.contains((char) c))
                .count();
        long consonants = str.chars()
                .filter(c -> !allVowels.contains((char) c))
                .filter(ch -> (ch >= 'a' && ch <= 'z'))
                .count();
        return Pair.of(vowels, consonants);
        */
        
        // or via partitioningBy()
        Map<Boolean, Long> result = str.chars()
                .mapToObj(c -> (char) c)
                .filter(ch -> (ch >= 'a' && ch <= 'z'))
                .collect(partitioningBy(c -> allVowels.contains(c), counting()));

        return Pair.of(result.get(true), result.get(false));
    }
}

Sample Output:

Input text: 
 ... Illinois Mathematics & Science Academy ... 

String.charAt() solution:
Execution time: 2905069 ns (2 ms)
Vowels: 14
Consonants: 19

Java 8, functional-style solution:
Execution time: 117485709 ns (117 ms)
Vowels: 14
Consonants: 19

Flowchart:

Java Code Editor:

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