VowelCounter.java

package module4.recursion.vowelcounter;

/**
 * VowelCounter
 */
public class VowelCounter {
    public static final char[] VOWELS = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'};
    /**
     * Uses recursive methods to count the number of vowels (a-e-i-o-u) in a word or phrase
     * @param str The string to count
     * @return The number of vowels to count
     */
    public static int vowelCount(String str) {
        if (str.length() == 0) {
            return 0;
        }
        int count = vowelCount(str.substring(1));
        if (str.substring(0, 1).matches("[aeiouAEIOU]" /* */)) {
            return count + 1;
        }   
        return count;
    }

    public static void main(String[] args) {
        System.out.println();
        System.out.println("=== RECURSIVE VOWEL COUNTER DEMO ===");

        final String[] demoStrings = {
            "AIUEOaiueo", "abab", "queueing", "buffalo", "4BS0L6T3LY L33T", "hachi machi", "hOnK hOnK mOtHeRfAtHeR", "bienvenue", "power bottoms"
        };
        for (String s : demoStrings) {
            System.out.printf("vowelCount(\"%s\") => %d\n", s, vowelCount(s));
        }
    }

}
/**
Console Output:

=== RECURSIVE VOWEL COUNTER DEMO ===
vowelCount("AIUEOaiueo") => 10
vowelCount("abab") => 2
vowelCount("queueing") => 5
vowelCount("buffalo") => 3
vowelCount("hachi machi") => 4
vowelCount("hOnK hOnK mOtHeRfAtHeR") => 6
vowelCount("bienvenue") => 5
vowelCount("power bottoms") => 4

 */