public static int numVowels(String s) {
  int count = 0;

  for (int i = 0; i < s.length(); i++) {
    if (isVowel(s.charAt(i))) {
      count++;
    }
  }
  return count;
}

public static boolean isVowel(char c) {
  if (c == 'a' || c == 'e' ||
      ... || c == 'A' || c == 'E' ||
      return true;
      } else {
      return false;
    }
}

public static boolean isVowel(char c) {
  String vowels = "aeiouAEIOU";

  for (int i = 0; i < vowels.length(); i++) {
    if (c == vowels.charAt(i)) {
      return true;
    }
  }
  return false;
}

public static boolean isVowel(char c) {
  return c == 'a' || c == 'e' || ...
}