please explain the code

Question is divided into 2 sections: 3.1 3.2 In this question the two sections should be solved with the help of recursion and no loops should be used at all! Private methods can be added (without loops). Note: In this question it is allowed to use the following methods from the String class: () substring (), length (), charAt. Do not use other methods from this class Write a class called Q3 that contains the following two methods (note that there are two sections on this question). public static String changeReverseLetters (String s) The method takes as a parameter a string named s and returns a new string which consists of the letters of 5 in reverse order and with the inverse Case. That is, the order of the letters in the string must be reversed and in addition each lower case in case 5 will appear as an upper case in the result and vice versa. The string 5 may contain any character (not just letters). For example, for "s =" Abcd1, the function returns the string "1dCBa