JAVA Given an array S of strings and a string str, you should check if any string in S is a prefix of str. If it is the case, then you return true, otherwise you return false. Write the java code of this method as an answer to this question. a string s1 is a prefix of a string s2 if s1 is a substring of s2. you are NOT ALLOWED to use any other string method than substring, length, charAt, equals

Given two strings s1 and s2, you should count and return the number of occurrences of s2 within s1. Write recursive java code to solve this problem. you are NOT ALLOWED to use any other string method than substring, length, charAt, equals.

Given an integer num, you should count and return the number of digits this integer has. Write recursive java code to solve this problem. you are NOT ALLOWED to Integer methods or to convert your int into a String.