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 int countletter (String word, char letter ) The method gets a string and a character and returns how many times a letter appears in a word. The method is case - Sensitive - that is, it counts the occurrences of the letter exactly as it appears. That is, if it is a lower case the method will find Only its occurrences as a lower case and if it is an uppercase case the method will only find its occurrences as a uppercase letter. For example: word=heLLOO and letter=0 the method returns 1 word=helLoO and the letter is L the method will return 2