Java获取首字符串大小写

    public static String firstCharToLowerCase(String str) {
        char firstChar = str.charAt(0);
        if (firstChar >= 'A' && firstChar <= 'Z') {
            char[] arr = str.toCharArray();
            arr[0] += ('a' - 'A');
            return new String(arr);
        }
        return str;
    }

    public static String firstCharToUpperCase(String str) {
        char firstChar = str.charAt(0);
        if (firstChar >= 'a' && firstChar <= 'z') {
            char[] arr = str.toCharArray();
            arr[0] -= ('a' - 'A');
            return new String(arr);
        }
        return str;
    }