COMP 401 Midterm Tuesday Oct 17 2017 11am 12 15pm Instructions 1 Please spread out and try and sit in alternate seats 2 This is a closed book exam 3 You will not be penalized for errors in Java syntax 4 Write on the exam itself Write on a blank page in particular the last page if there is not enough space to solve a problem and indicate you have done so 5 There are 8 numbered pages including this one and any marked blank pages 3 questions 80 possible points Point values appear in brackets next to each question 6 You are not required to comment or annotate any code you write but may get partial credit if you write appropriate 7 comments annotations but incorrect code If you need to make any assumptions to clarify a problem write your assumptions down Only reasonable assumptions get full credit 8 Please inform the proctor of anything in the exam that you think is a mistake 9 Your code will be evaluated not only for correctness but also for time and space efficiency and style 10 You cannot use any Java capabilities not covered in class 11 To answer questions about some piece of code given here you can mark the code directly 12 If you do not understand some English word do not hesitate to ask the proctor Naturally you are expected to know the computer science terms defined in class 13 Write clearly using a pen pencil with a dark color we will be scanning your exams 14 Please try and write in the allocated space as that will reduce mistakes in grading of scanned exams 15 Put your initials onyen in the header of each page in case the pages are separated Points have been allocated for writing the onyen and name clearly in capitals Q1 NAME ONYEN and EMAIL if it is not onyen live unc edu ALL CAPITALS PLEASE NAME 2 pts ONYEN 3pts EMAIL Pledge I have neither given nor received unauthorized aid on this exam signed For survey purposes please indicate the time at which you turned in the exam 1 5 2 31 3 34 4 10 Please do not write below Total 80 Initials Onyen 2 31 pts TRIMMING A STRING Implement a class Trimmer that implements a public static method called trim that takes a single String argument and returns a copy of the string with leading and trailing spaces these are prefix and suffix substrings containing only the space character removed The following main method and its output illustrates the use of this class Main method public static void main String anArgs System out println Empty string Trimmer trim System out println Space only Trimmer trim System out println Spaceless Trimmer trim hello 123 System out println Leading one space Trimmer trim hello 123 System out println Trailing one space Trimmer trim hello 123 System out println Variable spaces Trimmer trim hello 123 System out println Interleaved spaces Trimmer trim h e l l o Output Empty string Space only Spaceless hello 123 Leading one space hello 123 Trailing one space hello 123 Variable spaces hello 123 Interleaved spaces h e l l o Carefully understand what this class is supposed to do as it is used as a running example for the remaining two questions also which you can do in any order You can get full credit for the other questions without implementing any code in this question You can and are encouraged to not implement a single monolithic trim method To receive full credit you should follow all style principles with which you are familiar to create code that is easy to understand change and reuse and does not have duplication This means you are encouraged to implement additional meaningful public and or non public methods in the class that are called by trim You need not put these methods in another class To get full credit you must cover all cases and follow style rules You will get the vast majority of points even if you do not follow the style rules You will receive partial credit based on how many of the cases illustrated in the output are supported by your implementation However if you do not cover all cases you must tell us what these cases are For example if you cover only the first two cases write down on this page or in comments on the next page the following CASES COVERED Empty String Space only string This information will explain your code and lack of such information can result in erroneous solutions getting no credit The String instance methods you can use are public char charAt int index returns the char value at the specified index public int length returns the length of this string public String substring int beginIndex int endIndex Returns a new string that is a substring of this string The substring begins at the specified beginIndex and extends to the character at index endIndex 1 Thus the length of the substring is endIndex beginIndex You can of course use the String operator which returns a concatenation of its two operands You cannot use any other String method such as the built in String trim method which was not covered in class 2 Initials Onyen 3 Initials Onyen 3 34 pts UNDERSTANDING CODE Consider the following code which is repeated in the following question public interface DuplicatedString public String getString1 public String getString2 string aString public class ADuplicatedString implements DuplicatedString String string public ADuplicatedString String aString public ADuplicatedString public String getString1 public void setString1 String newVal public String getString2 return string return getString1 string newVal super aString public class ADuplicatedTrimmedString extends ADuplicatedString public ADuplicatedTrimmedString String aString public String getOriginalString public String getString1 return Trimmer trim super getString1 return string return aString System out println getString1 format aDuplicatedString getString1 System out println getString2 format aDuplicatedString getString2 public class DuplicatedTrimmedStringDriver public static String format String aString called by print public static void print ADuplicatedString aDuplicatedString called by main public static void main String args ADuplicatedString anUninitializedDuplicate print anUninitializedDuplicate ADuplicatedString anInitializedDuplicate print anInitializedDuplicate ADuplicatedTrimmedString anInitializedTrimmedDuplicate print anInitializedTrimmedDuplicate new ADuplicatedString new ADuplicatedString Hello single space prefix and suffix new ADuplicatedTrimmedString Hello single space prefix and suffix 4 Initials Onyen a 2 pts Name an instance variable in the given code b 2 pts Name a property in the given code c 2 pts