nextLetter()

/* Create a function NextLetter which takes a string parameter and
   modifies it using the following algorithm:Replace every letter in the string with the letter next
   but one in the alphabet (c becomes e, z becomes b, A becomes C).
   Ignore numbers and symbols. Then capitalize every vowel in this new string (a, e, i, o, u)
   and finally return this modified string. The string will not be empty and not include spaces.
   Examples

   1) Input-  £7eBm      Output- £7gDO
   2) Input-   Znb0y     Output- Bpd0A
 */

public class Sample {

    public static void main(String[] args) {
        String s = "Znb0y";
        System.out.println(nextLetter(s)); // Bpd0A
        System.out.println(nextLetter("abc")); //
        System.out.println(nextLetter("£7eBm")); // £7gDO
    }

    static boolean isVowel(char ch) {
        return ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o'
                || ch == 'u';
    }

    static String nextLetter(String s) {
        char[] temp = s.toCharArray();
        for (int i = 0; i < temp.length; i++) {
            if (Character.isLetter(temp[i])) {
                if (temp[i] != 'z' && temp[i] != 'Z' && temp[i] != 'y' && temp[i] != 'Y') {
                    temp[i] = (char) (temp[i] + 2);
                    if (isVowel(temp[i])) {
                        temp[i] = Character.toUpperCase(temp[i]);
                    }
                } else { // if letter is z, Z, y, Y
                    if (temp[i] == 'z') {
                        temp[i] = 'b';
                    }
                    if (temp[i] == 'Z') {
                        temp[i] = 'B';
                    }
                    if (temp[i] == 'y' || temp[i] == 'Y') {
                        temp[i] = 'A';
                    }
                }
            }
        }
        return String.valueOf(temp);
    }


    public static boolean starredLetters(String s) {
        // checks if String is empty
        if (s.isEmpty()) {
            return false;
        } else { // string is not empty
            // checks if String has at least one letter
            for (int j = 0; j < s.length(); j++) {
                if (Character.isLetter(s.charAt(j))) {
                    break;
                }
            }
            int num = 0;
            for (int i = 0; i < s.length(); i++) {
                if (Character.isLetter(s.charAt(i))) {
                    if ((i - 1) != -1 && (i + 1) < s.length()) {
                        if (s.charAt(i - 1) != '*' || s.charAt(i + 1) != '*') {
                            return false;
                        }
                    } else {
                        return false;
                    }
                } else {
                    num++;
                    if (num == s.length()) {
                        return false;
                    }

                }
            }
        }
        return true;
    }
}