in java pleas, MUST USE RECURSION TO SOLVE

public String dupEachChar (ArrayList str) This method takes an ArrayList of characters and returns a string that consists of two of each of the characters-in the ArrayList. In addition, these duplicates are added to the ArrayList. If the ArrayList is empty, an empty string is returned and no characters are added to the ArrayList. Example (note the 'and " below are used to denote contents and are not part of the data) If an ArrayList containing 'a','b', and 'c' is passed to the method, the method would return "aabbcc" back as a String. In addition, the ArrayList would now have 6 elements instead of 3 matching the characters in the return string and in the same order