Java programming 1) a) write the recursive function int digitSum (int n), which gets the positive integer n and returns the sum of individual digits in it. For example, if called by the digitSum (234), it returns 9 (= 2 + 3 + 4). Note that if n is an integer, n% 10 returns the first digit to n (234% 10 is 4) and that n / 10 takes away the last digit in n (234/10 is 23). Also write a short main case that tests your function. b) The first numbers in the Threebonacci series are 0, 0, 1, 1, 2, 4, 7, 13, 24, ... Write two functions to calculate the n Threebonacci numberone recursive (tribRec (int n), but the other not recursive (tribo (int n). Also write a main-case that receives one positive integer of the command line, calling both functions and prints the result. Please write the full code