Modify your UserProfile class to meet the following requirements:
Note that wall postings should be stored in reverse-chronological order, meaning that newly created posts should be stored at the beginning of the list, not at the end. Also, this method should ensure that the total number of posts does not exceed 20. Once the wall gets that full, delete the oldest post to make room for a new one. Study the API documentation for ArrayList to find suitable methods to accomplish this arrangement. You may assume that the clock is consistent, that is, postings created more recently will also have a more recent time stamp.