private static final Set<Character> VOWELS = new HashSet<>();

static {

VOWELS.add('a');

VOWELS.add('e');

VOWELS.add('i');

VOWELS.add('o');

VOWELS.add('u');

VOWELS.add('A');

VOWELS.add('E');

VOWELS.add('I');

VOWELS.add('O');

VOWELS.add('U');

}

public static String reverseVowels(String string) {

List<Character> vowels = getVowels(string);

StringBuilder result = new StringBuilder();

for (int index = 0, j = vowels.size() - 1 ; index < string.length() ; index++) {

char character = string.charAt(index);

result.append((char) (isVowel(character) ? vowels.get(j--) : character));

}

return result.toString();

}

private static boolean isVowel(char character) {

return VOWELS.contains(character);

}

private static List<Character> getVowels(String string) {

List<Character> vowels = new ArrayList<>();

for (int index = 0 ; index < string.length() ; index++) {

char character = string.charAt(index);

if (isVowel(character)) {

vowels.add(character);

}

}

return vowels;

}