public class Vowels {
    public static void main(String[] args) {
        System.out.println("a is vowel? " + isVowel("a"));
        System.out.println("z is vowel? " + isVowel("z"));
                       
        System.out.println("oink has vowel? " + hasVowel("oink"));
        System.out.println("gypsy has vowel? " + hasVowel("gypsy"));
        
        //System.out.println("OUI is all vowels? " + isAllVowels("OUI"));
        //System.out.println("gypsy is all vowels? " + isAllVowels("oink"));        
    }
    
    // This method returns whether or not the given string contains a vowel.
    public static boolean hasVowel(String s) {
        for (int i = 0; i < s.length(); i++) {
            String nextChar = s.substring(i, i + 1);
            
            if(isVowel(nextChar)) {
                return true;
            }
        }
        
        return false;
    }
    
    // This method returns whether or not the given string is a vowel.
    // This method uses "Boolean Zen".
    public static boolean isVowel(String s) {
        return s.equalsIgnoreCase("a")
            || s.equalsIgnoreCase("e")
            || s.equalsIgnoreCase("i")
            || s.equalsIgnoreCase("o")
            || s.equalsIgnoreCase("u");
    }
}