University of Maryland College Park Department of Computer Science CMSC131 Spring 2019 Exam 2 Key FIRSTNAME LASTNAME PRINT IN UPPERCASE STUDENT ID e g 123456789 Instructions Please print your answers and use a pencil This exam is a closed book closed notes exam with a duration of 50 minutes and 200 total points Do not remove the exam s staple Removing it will interfere with the scanning process even if you staple the exam again Write your directory id e g terps1 not UID at the bottom of pages with the text DirectoryId provide answers in the rectangular areas and do not remove any exam pages Even if you don t use the extra pages for scratch work return them with the rest of the exam If you continue a problem on the extra page s provided make a note on the particular problem For multiple choice questions you can assume only one answer is expected unless stated otherwise You don t need to use meaningful variable names however we expect good indentation You must write your name and id at this point we will not wait for you after time is up You must stop writing once time is up Grader Use Only 1 2 3 Total Problem 1 Miscellaneous Problem 2 Memory Map Problem 3 Class Implementation Total 48 50 102 200 1 Problem 1 Miscellaneous 1 3 pts A method should be defined as static if circle all that apply It does not access instance variables If it is a public method a b c The method makes a reference to special value this d None of the above 2 3 pts How many objects exist in the following code fragment Answer a StringBuffer m Answer 0 3 3 pts Instance variables are created when a An instance of the class is created b When the constructor is called c When a set method is called d None of the above 4 3 pts Which of the following actually creates an object Answer a a new b constructor c private d None of the above Answer a 5 3 pts We can call a non static method of a class circle all that apply a Only if an object of the class has already been created b From a static method of the class c By using the class name e g ClassName method d None of the above Answer a or b or both have a It has the same value a has b It has the same value b has c It has the value null d None of the above Answer a 2 6 3 pts When we call a completeTask b which value does the special value this present inside of the completeTask method 7 3 pts What is the output of the following program public class Values private String distance private double cost private boolean completed public static void main String args Values values new Values System out println values distance System out println values cost System out println values completed Answer null 0 0 or 0 False Answer Yes 9 a Heap b Stack c main method d None of the above 8 3 pts In the previous Values class is there a default constructor associated with the class Yes No 3 pts Where can primitive type variables reside in Java Circle all that apply Answer a and b if they mark c do not penalize 10 3 pts If you define a JUnit test and don t add any assertions e g assertTrue then a The test will fail when it is run b The test will succeed when it is run c The test will not compile d None of the above Answer b not affect the original To make the copy 11 3 pts We have an array of StringBuffer objects and we would like to make a copy of the array so changes to the new array will a We need to make a deep copy otherwise changes in the new array will affect the original b A shallow copy where we only duplicate the array object and not the StringBuffer objects is enough c A reference copy is enough d None of the above 12 3 pts The code in the finally block is executed a After a catch clause has been executed b When two or more exemptions take place c Before the try block d None of the above Answer a Answer d 3 13 3 pts When we execute the following code System out println 14 90 14 80 10 Hello Bye a We will always get Hello b Getting Bye is possible as some numbers cannot be represented precisely in binary c The expression within the System out println does not compile d None of the above Answer b 14 3 pts The class Toy needs to implement the equals method Which of the following is the correct prototype first line of the method for the equals method needed by this class a public boolean equals Object obj b public boolean equals Toy obj c public boolean equals String obj d None of the above Answer a int x Answer int 49 Math random 2 15 6 pts Math random returns a value between 0 inclusive and less than 1 Complete the following assignment so x is assigned a random integer value between 2 inclusive and 50 inclusive The only function you can use is Math random 4 Problem 2 Memory Map Draw a memory map for the following program at the point in the program execution indicated by the comment HERE Remember to draw the stack and the heap If an entry has a value of null write NULL If an entry has a value of 0 do not leave it blank write 0 public static void process StringBuffer data int size int delta data 0 new StringBuffer Tom data 1 append 131 size 20 delta 1000 HERE public static void main String args StringBuffer all new StringBuffer 2 int length 10 int col 4 500 7 all 0 new StringBuffer Dora all 1 new StringBuffer Elsa process all length col 1 length data size length 1500 delta 500 col all 20 10 3 7 4 args Elsa131 Tom length 0 length 2 5 Problem 3 Class Implementation Complete the implementation of a class called Account that represents a bank account A bank account has an id a password a balance and an array of integers deposits representing deposits done to the account The maximum size of the array is MAX DEPOSITS and the current number of deposits made is represented by numDeposits Below we have provided a driver that illustrates the functionality associated with the class Feel free to ignore it if you know what to implement The driver relies on methods e g toString you don t need to implement You MAY NOT add any methods beyond the ones specified below not even private if you do you will lose credit public class Account public static final int MAX DEPOSITS 100 private StringBuffer password private int id balance numDeposits private int deposits Account a1 new Account 1 terpsrock 20 …
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