Name USC loginid e g ttrojan CS 455 Midterm Exam 1 Fall 2011 Bono Sept 28 2011 There are 5 problems on the exam with 53 points total available There are 7 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 If you have scratch work in addition to your answer circle your final answer so we know what to grade Put your name and USC loginid at the top of the exam Please read over the whole test before beginning Good luck Remote DEN students only Do not write on the backs of pages If additional space is needed ask proctor for additional blank page s put your name on them and attach them to the exam value Problem 1 10 pts Problem 2 10 pts Problem 3 10 pts Problem 4 8 pts Problem 5 15 pts TOTAL 53 pts score A Problem 1 10 pts Consider the following program Note more about Point class on code handout public class Prob1 public static Point foo Point a a translate 3 4 return a public static void main String args Point p1 new Point 10 40 Point p2 new Point foo p1 Point p3 foo p2 System out println p1 p2 p3 Part A 5 In the space below draw a box and pointer diagram a k a memory diagram showing all object variables objects and their state as they have changed during the code sequence This includes showing foo s parameter a Because foo is called multiple times you can distinguish the formal parameters from the different calls with subscripts a1 a2 Part B 3 What is printed by the code For the purpose of this problem assume a Point is printed as follows x y Part C 2 How many Point objects are created by the code above 2 Problem 2 10 pts Let s consider a class similar to our Drunkard class from pa1 but that only can move in a onedimensional space that is along the integer number line We ll call this class Drunkard1D This class will otherwise have the same functionality as our old Drunkard except that the size of the step it takes each time is also random It will take a step whose size will range from 1 to Drunkard1D MAX STEP SIZE inclusive Implement the whole class the class itself interface documentation and space for your answer is given on the next page For this problem you will be evaluated on class design style issues as well as code correctness Here s some sample code that uses our new class and corresponding output Drunkard1D d new Drunkard1D 3 System out print d getCurrentLoc print initial location 3 for int i 0 i numSteps i d takeStep System out print d getCurrentLoc Sample output actual output depends on what random sequence gets generated 3 5 1 7 2 0 Hint Random class interface given on the code handout Problem continued on the next page 3 Problem 2 cont Complete the implementation of Drunkard1D details of this problem are on the previous page Represents a drunkard doing a random walk on an integer number line Drunkard chooses direction and step size randomly Steps range in distance from 1 and MAX STEP SIZE inclusive public class Drunkard1D public static final int MAX STEP SIZE 10 Creates drunkard with given starting location param startLoc starting location of drunkard public Drunkard1D int startLoc Takes a random length step see class comment above in one of the two possible directions along the number line Changes the current location of the drunkard public void takeStep gets the current location of the drunkard return an int representing drunkard s current location public int getCurrentLoc 4 Problem 3 10 pts Implement the static method readAndValidate which takes as its parameters a scanner and a range of valid values The method prompts for a value in the range given reads the int from the scanner given and validates that the value is in the range By validate we mean that it checks that the value read in was in the correct range and if it wasn t it prints out an error message and prompts and reads again until the user enters a valid value The method then returns this value You may assume that users will always enter an int at your prompt e g you do not have to handle a user typing a letter by mistake Your output should follow the examples below user input is in italics Ex1 Interaction for an example call to readAndValidate this call returns 7 Enter int 1 7 3 ERROR 3 not in range Enter int 1 7 0 ERROR 0 not in range Enter int 1 7 7 Ex2 Interaction for a second example call to readAndValidate this call returns 3 Enter int 1 7 3 Prompts for reads and validates integer data from user See above for detailed description and examples of behavior param in the Scanner to read from param low the lower bound of valid range inclusive param high the upper bound of valid range inclusive return the validated integer read from user public static int readAndValidate Scanner in int low int high 5 Problem 4 8 pts total Suppose the following is a program a student wrote to solve the problem of figuring out how many students from a class got each score on a lab worth 4 points when given a list of lab scores The program is not required to do any error checking i e assume valid input The student solution doesn t do what it is supposed to do Java hint the new int expression also initializes the array see code handout public static void main String args Scanner in new Scanner System in System out print Please enter number of scores int numScores in nextInt int counts new int numScores System out println Please enter the scores for int i 0 i numScores i int score in nextInt counts i counts i score System out println Score reports the results in a table How many got that score for int i 0 i counts length i System out println i counts i spaces are to make columns line up Part A Show the output that would be produced by this program for the input given below I e output of running program presented here not a fixed version of the program 7 4 3 4 4 0 4 3 Part B Fix the program so the program does what it was supposed to do see problem description at the top of the page Show your changes directly in the code above I e use arrows if necessary going from new code pointing to the exact location where it would be inserted cross out anything that would get removed or changed Your new version must work with the same input format as the old one 6 Problem 5 15 pts total Implement …