대문자와 소문자

class Solution { public String solution(String my_string) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < my_string.length(); i++) { if (my_string.charAt(i) >= 'a' && my_string.charAt(i) <= 'z') { sb.append(String.valueOf(my_string.charAt(i)).toUpperCase()); } else if (my_string.charAt(i) >= 'A' && my_string.charAt(i) <= 'Z') { sb.append(String.valueOf(my_string.charAt(i)).toLowerCase()); } } return sb.toString(); } }