University of Maryland College Park Dept of Computer Science CMSC131 Fall 2018 Exam 3 Key FIRSTNAME LASTNAME PRINT IN UPPERCASE STUDENT ID e g 123456789 Instructions Please print your answers and use a pencil Do not remove the staple from the exam Removing it will interfere with the Gradescope scanning process To make sure Gradescope can recognize your exam print your name write your directory id at the bottom of pages with the text DirectoryId provide answers in the rectangular areas provided and do not remove any exam pages Even if you use the provided extra pages for scratch work they must be returned with the rest of the exam This exam is a closed book closed notes exam with a duration of 50 minutes and 200 total points Your code must be efficient You don t need to use meaningful variable names however we expect good indentation Grader Use Only 1 2 3 4 Total Problem 1 Miscellaneous Problem 2 Memory Map Problem 3 Arrays Problem 4 String Manipulation Total 42 42 64 52 200 1 3 pts What is the output for the following code fragment Problem 1 Miscellaneous 1 int k 1 m 1 while k 1 System out println Done while m 1 System out println Hi k if m 1 m break 2 3 pts Appending concatenating strings is a An expensive operation and an alternative e g StringBuffer should be used b A cheap operation c An operation that have the same performance as using a StringBuffer d None of the above 3 3 pts When we execute the following code System out println 3 9 3 8 10 a We will always get true b Getting false is possible as some numbers cannot be represented precisely in binary c An exemption will be thrown d None of the above Answer Hi Done Answer a Answer b Answer True Answer True Answer False 4 5 2 3 pts When an exception occurs Java pops back up the call stack to each of the calling methods to see whether the exception is being handled in a catch block of the method True or False 3 pts In a JUnit test method if you don t provide an assertion the test is considered to have succeeded True or False 3 pts Creating an array of size 0 is not allowed in Java True or False 6 5 pts The following class has a privacy leak Fix the code to remove it feel free to edit and cross out the code provided 7 3 pts The code in the finally block is executed a Only when no exemption takes place b Always c Only when the exemption takes place d None of the above Answer b 8 private StringBuffer data public Example String dataIn data new StringBuffer data append dataIn public StringBuffer getData return data public class Example Answer getData method will return a copy of data 9 3 pts We have an array of string objects and we would like to make a copy of the array so changes to the new array will not affect the original To make the copy 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 string objects is enough c A reference copy is enough d None of the above 10 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 1 inclusive and 100 inclusive The only function you can use is Math random One Possible Answer int Math random 100 1 11 7 pts Rewrite the following code fragment by replacing the if statement with the ternary operator Answer b int x Original Code String name int y scanner nextInt if y 0 name Pos else name Neg Rewritten Code String name int y scanner nextInt name Answer name y 0 Pos Neg 3 double b 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 value write NULL If an entry has a value of 0 do not leave it blank write 0 public static void process StringBuffer a a 0 append bert StringBuffer m a 0 a 0 null b 9 HERE public static void main String args StringBuffer all new StringBuffer 3 double tem new double 2 all 0 new StringBuffer all 0 append Al all 1 new StringBuffer all 1 append Bud tem 0 23 4 process all tem 0 length length Solution 23 4 2 0 m b a tem all args 9 3 NULL NULL Albert Bud 4 Problem 3 Arrays Implement a method named getIndicesArray that has the prototype below The method returns an array with the INDICES of elements in the data array that have a value less than or equal to limit For this problem You may only perform a single pass over the array The array to return must have a length that corresponds to the length of the data array plus one The last index added to the result array will be followed by 1 in order to mark the end of data If the data parameter is null the method will throw the exemption IllegalArgumentException with the message Invalid and no further computation will take place Below we included a driver and the corresponding output that relies on the method getIndicesArray Feel free to ignore if you know what to implement One Possible Answer public static int getIndicesArray int data int limit if data null int answer new int data length 1 throw new IllegalArgumentException Invalid int k 0 for int i 0 i data length i answer k 1 if data i limit answer k i return answer 5 Problem 4 String Manipulation Implement a method named getSerialNumber that has the prototype below The method will process a string and extract an integer that is part of a valid string A valid string is one that starts with the uppercase letter A and is followed by a 5 digit number Any number of spaces can precede A and follow the last digit For example A24567 is a valid string A235B7 and A234 are invalid The getSerialNumber method returns the integer that is part of a valid string parameter and 1 if the string parameter is an invalid string or null For this problem You can use the trim method to remove any blank spaces surrounding the parameter You need to use the method Integer parseInt to transform to an integer the substring that is part of a valid string If the NumberFormatException is thrown you can then return 1 You can use the String class substring method to retrieve the appropriate substring The following information is from the begins at the specified beginIndex and extends to the character at index endIndex 1 public String substring int beginIndex int endIndex Returns a string that is a …
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