/*
 * RemoveVowels.java
 *
 * Computer Science S-111
 *
 * A class that contains a recursive method for removing all
 * lower-case vowels that appear in a string.
 */

public class RemoveVowels {
    /*
     * removeVowels - a recursive method that returns 
     * string formed by removing all lower-case vowels
     * (a, e, i, o, u) from the String str.
     */
    public static String removeVowels(String str) {
        // base cases
        if (str == null) {
            return null;
        } else if (str.equals("")) {
            return "";
        } else {
            // recursive case
        
            // Make a recursive call to remove vowels from the
            // rest of the string.
            String removedFromRest = removeVowels(str.substring(1));
        
            // If the first character in str is a vowel,
            // we don't include it in the return value.
            // If it isn't a vowel, we do include it.
            char first = str.charAt(0);
            if (first == 'a' || first == 'e' || first == 'i' ||
              first == 'o' || first == 'u') {
                return removedFromRest;
            } else {
                return first + removedFromRest;
            }
        }
    }
}