[프로그래머스/Java] 대문자와 소문자

-Code

import java.util.stream.Collectors;

class Solution {
    public String solution(String my_string) {
        return my_string.chars()
                .mapToObj(el -> (char) el)
                .map(c ->
                        Character.isUpperCase(c) ?
                                Character.toLowerCase(c) :
                                Character.toUpperCase(c)
                ).map(String::valueOf)
                .collect(Collectors.joining(""));
    }
}