不使用自带函数字符串大小写转换

private static void (String str) {

    char[] toUpper = str.toCharArray();
    char[] toLower = toUpper.clone();

    for (int i = 0; i < toUpper.length; i++) {
        char point = toUpper[i];
        if (point >= 97 && point <= 122) {
            
            toUpper[i] = (char) (point - 32);
        }
        if (point >= 65 && point <= 90) {
            // 大写
            toLower[i] = (char) (point + 32);
        }
    }
    System.out.println("upper:" + new String(toUpper));
    System.out.println("lower:" + new String(toLower));
}