Name USC loginid e g ttrojan CS 455 Midterm Exam 1 Fall 2012 Bono Oct 3 2012 There are 4 problems on the exam with 50 points total available There are 6 pages to the exam including this one make sure you have all of them There is also a one page code handout that accompanies the exam If you need additional space to write any answers you may use the backs of exam pages just direct us to look there Note if you give multiple answers for a problem we will only grade the first one Avoid this issue by labeling and circling your final answers and crossing out any other answers you changed your mind about though it s fine if you show your work Put your name and USC loginid at the top of the exam Please read over the whole test before beginning Good luck value Problem 1 11 pts Problem 2a 12 pts Problem 2b 2 pts Problem 3 10 pts Problem 4 15 pts TOTAL 50 pts score Problem 1 11 pts total Consider the following program public class Prob1 public static void foo int i int vals Output of Program i vals i System out println i Arrays toString vals public static void main String args int j 1 int arr new int 3 foo j arr System out println j Arrays toString arr j foo j arr System out println j Arrays toString arr Part A In the space below draw a box and pointer diagram a k a memory diagram showing all variables objects arrays and their state as they have changed during the code sequence You may identify the data in the first call to foo as follows i1 vals1 and for the second call i2 vals2 When a value gets updated cross it out and show the new value next to the old one rather than drawing it again e g you will only have one box labeled arr and one box labeled j Part B In the box to the right of the code above show the output of the program 2 Problem 2 14 pts total Part A 12 Complete the implementation of the class Duration which represents some amount of time in hours and minutes such as 3 hours and 25 minutes not a time of day Such a class could be a useful building block in an applications such as a timer stopwatch or scheduling programs e g to schedule your DVR or flights for an airline The class allows us to create a duration expressed using a number of hours and minutes or just total number of minutes it also allows us to increase a duration by some amount of time to add two durations together and to convert a duration to a String form for printing or appending to larger messages The detailed specification for each method appears in its method comments below Furthermore you are restricted to use the internal representation for Duration shown in the starter code for the class internally we will store a duration as its total number of minutes This representation actually would be one an implementer would likely use in a more fleshed out version of such a class because makes some operations easier to implement The class interface and space for your answer starts here and continues onto the next page Duration represents some amount of time in hours and minutes public class Duration Problem restriction do not change the private instance variable definitions private int totMinutes representation invariant totMinutes 0 Creates duration of the given hours and minutes PRE hours 0 and minutes 0 public Duration int hours int minutes Creates a duration given as a total number of minutes PRE minutes 0 public Duration int totalMinutes 3 Problem 2 cont Increase the current duration by the amount of time given by hours and minutes PRE hours 0 and minutes 0 public void increase int hours int minutes Returns the sum of this duration and duration b This method is not a mutator does not modify this Note the return type is a Duration object HINT Java rules allow this method to access private data of other Duration objects besides this for example b s private data public Duration add Duration b Returns a String form of the duration using the format shown by example here 8hrs 32min public String toString Part B 2 Are Duration objects immutable If so why if not why not 4 Problem 3 10 pts Implement a new private method for our Names class called isValidNames which returns true if and only if the internals of this Names object is in a valid state that is it satisfies its representation invariant Such a method is useful to check that the code in your other Names methods works correctly We re using the same Names class and representation we discussed in lecture and that is reviewed below Stores a list of unique names in alphabetical order Allows look up insert and removal of elements in the list public class Names private String namesArr the capacity is namesArr length private int numNames the number of names in the array Representation invariant 0 numNames namesArr length when numNames 0 the names are stored in namesArr 0 through namesArr numNames 1 the names stored are unique the names are in alphabetical order private boolean isValidNames 5 Problem 4 15 pts total Implement the static method mode which returns the value that occurs most often in an array of integers You may assume the array has at least one element and all of the values in the array are in the range 0 100 If there is more than one value that occurs most often return the smallest such value See Ex2 below Here are some examples arr return value of mode arr Ex1 99 86 99 99 95 86 99 Ex2 23 15 15 74 23 15 Ex3 76 76 two 15 s and two 23 s chooses the smallest value For full credit your answer must only traverse the data in arr once Hint you are allowed to use additional memory Returns the mode of the values in the array If there is more than one mode returns the smallest one PRE arr length 0 and all the values in arr are in the range 0 100 public static int mode int arr 6