Write an implementation that returns whether a String has vowels (English language) in alphabetical (A-Z) order or not.


  • Is my vowels variable appropriate? Is there a better way to implement a vowel lookup?
  • If a candidate String has no vowels, the validator will return true - is that reasonable? From a logical perspective, the program isn't lying, but you could make the same argument if it returned false. Would it be better to return an exception - something like NoVowelsInCandidateException?


public class VowelOrderValidator {
    private static final List<Character> vowels = new ArrayList<>(
            Arrays.asList('A', 'E', 'I', 'O', 'U', 'Y')

    public static boolean areVowelsOrdered(final String candidate) {
        final char[] chars = candidate.toUpperCase().toCharArray();
        int lastVowelIndex = 0;
        for (final char c : chars) {
            final int lookupIndex = vowels.indexOf(c);
            if (-1 != lookupIndex) {
                if (lookupIndex < lastVowelIndex) {
                    return false;
                } else {
                    lastVowelIndex = lookupIndex;


        return true;
  • \$\begingroup\$ As a side-note, matching the lowercase candidate against the following regular expression would work :) : "[^aeiouy]*(?:a[^eiouy]*)?(?:e[^aiouy]*)?(?:i[^aeouy]*)?(?:o[^aeiuy]*)?(?:u[^aeioy]*)?y?[^aeiou]*" (but I find it really less readable!) \$\endgroup\$
    – Tunaki
    Feb 7, 2016 at 18:39
  • 1
    \$\begingroup\$ Not a review, but I suggest Java 8, in cases like this it cuts down a ton of code. \$\endgroup\$
    – Caridorc
    Feb 7, 2016 at 21:48

1 Answer 1

  • Since vowels is a constant for your program, the convention would be that its name is in all uppercase, like VOWELS.
  • Take great care when uppercasing Strings:

    final char[] chars = candidate.toUpperCase().toCharArray();

    Uppercasing a String depends on the locale. By not specifying a locale, you are relying on the default locale of the JVM, which may cause problems for Turkish users (for example). It would be better to specify the ROOT locale:

    final char[] chars = candidate.toUpperCase(Locale.ROOT).toCharArray();
  • I'm not a big fan of inversing the conditions in an if:

    if (-1 != lookupIndex) {

    The following would be easier to read:

    if (lookupIndex != -1) {

    In fact, it would be even better to not check against -1 but test that the result is positive:

    if (lookupIndex >= 0) {

    It decouples the fact that indexOf returns -1 from what you really want to test, which is that the index was found.

  • I think returning true when there is no vowels is the least surprising result: when there are no vowels, then they all are in the right order. Throwing an exception would be a bad idea: no vowels in a String is not a real exceptional condition.

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