CS365 Midterm -- Spring 2019

Transcription

1 CS365 Midterm -- Spring This exam is closed-note, closed-book. 2. You must answer all of the questions. 3. The exam has 120 points and you will be scored out of 120 points. For example, if you score 100/120, you will receive an 83 for the exam. 4. Answer the questions on the exam itself and hand in the exam. 5. Good luck! 1. (16 points: General content) For each question below, look at the following list of items and fill in the blank with the best choice(s). package extends import virtual method interface type namespace replicated inheritance class finally final multiple inheritance public Scanner const shared inheritance protected subclasses static generational collector composition inheritance iterator stop-and-copy collector Error Throwable Exception RuntimeException IOException event interrupt non-virtual method implements classpath include filepath import try throw reference counting catch friend polymorphism mark-and-sweep collecto a. The keyword used in C++ to group similar classes, functions, and identifiers into a "module" so that the global scope can be sub-divided into multiple subscopes, thus allowing the re-use of names. b. The technique I can use in Java to inherit a class's implementation but not its interface. The technique stores an instance of the class and delegates implementation to the class's methods. c. The following form of garbage collection uses a three step algorithm in which the garbage collector 1) walks through the heap and marks every block as "useless", 2) for each pointer outside the heap performs a depth-first search and marks all blocks that are encountered as "useful", and 3) walks through the heap again and moves every block still marked as "useless" to the free list. d. Suppose in C++ I want class D to multiply inherit from two superclasses, B and C, and that B and C both inherit from A. If I want D to contain only one copy of A, what type of inheritance do I want? e. The keyword used in Java to declare the module to which a class belongs. 1 of 10 3/4/19, 12:15 PM

2 f. This construct allows a user to declare an abstract type in Java g. The Java super class for all exceptions which the compiler checks to ensure that they are either caught in a catch statement or else declared to be thrown out of a function by the "throws" keyword. h. The type of clause you can put at the end of a Java exception handler whose code will be executed regardless of whether or not the try block succeeds or fails. All multiple choice questions are 4 points each 2. What advantage is provided by inheritance? 3. a. It allows one class to base its implementation on the implementation of another class without also having to accept that class's API (application programmer interface). b. It allows a group of cooperating classes to implement an algorithm or data structure, such as a linked list or tree, by mutually sharing their implementation, while protecting their implementation from the outside world. c. It allows shared, common code to be factored into a superclass, thus simplifying program maintanance since only one copy of a common, shared function must be modified rather than multiple copies of that function. d. It allows a programmmer to inherit a class's implementation but not that class's interface by storing an instance of the class and delegating the implementation to the class's methods. How would you declare an integer method named addinterest to be a pure virtual method in Java? a. int addinterest(int amount) = 0; b. virtual int addinterest(int amount) = 0; c. abstract int addinterest(int amount); d. abstract virtual int addinterest(int amount); 4. If a Java member variable does not have an access modifier, such as public, then what is it's level of protection? a. private b. protected c. package d. public 5. When presenting textual data on a computer display, what type of font should you use to ensure that even on low-resolution screens, the text can be easily read? a. serif b. sans-serif c. typewriter d. fixed-width 2 of 10 3/4/19, 12:15 PM

3 6. 7. What is the name given to the technique that attempts to reduce the size of an image by omitting information that is considered less significant? a. sampling b. lossless compression c. lossy compression d. blurring When I digitize content, I may need to convert an analog signal to a discrete signal by periodically observing the value of the analog signal. What term is given to this observation process? a. sampling b. sensing c. discretization d. scissoring 8. Suppose that I have the following html tag: <p id = "first"> If I want to make the text in this paragraph be colored blue, which of the following CSS declarations should I use? a..first { color: blue; b. p.first { color: blue; c. first { color: blue; d. #first { color: blue; Suppose that I want to insert a link to the web-page into my html document. Which of the following html fragments should I use? a. <link href=" b. <goto href=" c. <href link=" d. <a href=" Social media companies often use this type of storage management technique to store sparse, semistructured data: a. document collections b. digital libraries c. hypertext d. databases 3 of 10 3/4/19, 12:15 PM

4 11. Which of the following code fragments correctly declares a generic Java class named HashMap that has: two type parameters for a key and a value. two instance variables named key and value with the key and value types respectively. a find function that takes a key as an argument and returns its corresponding value. a. class HashMap { K key; V value; public V find(k k) {... b. template <class K, class V> class HashMap { K key; V value; public V find(k k) {... c. class HashMap<K, V> { K key; V value; public V find(k k) {... d. class<k, V> HashMap { K key; V value; public V find<k, V>(K k) { Why is it not possible to create a generic Java data structure that stores primitive types? a. The data must be stored using pointers to heap-allocated objects and primitive types cannot be allocated off the heap. b. Java uses type-erasure to convert all generics to work on objects of type Object and primitive types are not Objects. c. Java uses downcasts to convert the generic types back to their original types and downcasts cannot be used with primitive types. d. Java passes parameters by value and not reference and hence it is not possible to modify primitive types because you are modifying their copy, rather than their original value. 4 of 10 3/4/19, 12:15 PM

5 13. (4 points) What is the output of f.type() in the following, abbreviated, C++ program: f.type(): class fruit { public: void type() { printf("fruit\n"); ; class apple : public fruit { public: void type() { printf("apple\n"); ; int main() { fruit *f = new apple(); f->type(); Multiple Answer Questions: Each question lists the number of correct answers. If you select more than the specified number, you will lose 1 point for each additional answer that you select. 14. (4 points) Suppose you have the following Java interfaces and classes: interface CheckingAccount {... interface SavingsAccount {... abstract class Account implements CheckingAccount, SavingsAccount { class BasicChecking extends Account {... class PremierChecking extends BasicChecking {... Circle all of the following declaration that are legal (4 correct answers): a. Account myaccount = new Account(); b. Account myaccount = new PremierChecking(); c. CheckingAccount myaccount = new BasicChecking(); d. CheckingAccount myaccount = new BasicChecking(); BasicChecking acct = myaccount; e. BasicChecking myaccount = new PremierChecking(); f. BasicChecking myaccount = new Account(); g. Account myaccount = new CheckingAccount(); h. BasicChecking myaccount = new CheckingAccount(); i. PremierChecking myaccount = new BasicChecking(); j. SavingsAccount myaccount = new PremierChecking(); 5 of 10 3/4/19, 12:15 PM

6 15. (4 points) Modules (i.e., packages) provide which of the following advantages in Java? Circle all correct answers (2 correct answers): a. They permit the implementation of subtype polymorphism b. They permit the implementation of parametric polymorphism c. They partition the namespace so that the same name can be used more than once d. They prevent subclasses from accessing member variables that you want to keep private. e. They allow a group of cooperating classes to share their implementation without having to make the implementation accessible to the outside world. f. They allow shared code to be factored into a superclass g. They allow exceptions to be thrown out of a class without causing the compiler to complain. 16. (7 points) In C++, I have the following class declarations: class MemoryException; class BadAllocException : public MemoryException; class PtrException : public MemoryException; class NullPtrException : public PtrException; class BadAddressException : public PtrException, std::exception; and the following throw statement: throw BadAddressException(); Which of the following catch clauses can catch this exception? Circle all that apply (7 correct answers). a. catch (MemoryException) b. catch (BadAllocException) c. catch (PtrException) d. catch (NullPtrException) e. catch (BadAddressException) f. catch (BadAddressException *) g. catch (BadAddressException &) h. catch (std::exception) i. catch (...) j. catch (default) k. catch (const MemoryException &) 6 of 10 3/4/19, 12:15 PM

7 17. (General Java:) Answer the following short code questions. a. (8 points) Declare a Java class named Circle that: a. is a subclass of a class named GraphicalObject, b. supports an interface named Printer, c. has two protected integer instance variables named center and radius, d. has a public void, non-virtual method named print that takes no arguments and that outputs center and radius on separate lines. Each variable should be preceeded with "center = " or "radius = ". b. ( 4 points) Write a Java code fragment to declare and create an array of 10 Circles. Name the array dots. 7 of 10 3/4/19, 12:15 PM

8 c. (10 points) Suppose you have a Java listnode declared as follows: class listnode { int value; listnode next; listnode prev; Write a Java function named insert that takes two arguments, a listnode named target and an integer named newvalue. insert should create a new listnode that stores newvalue and insert it before target in the list. You may assume that target's prev and next fields are not null. insert should return the newly created listnode. 8 of 10 3/4/19, 12:15 PM

9 18. (10 points) You are given the following abbreviated declarations. package animal has the following classes: class Bear { protected int a; int b; class Dog { Bear cuddly = new Bear(); void print() { System.out.println(cuddly.a, cuddly.b); class Grizzly extends Bear { void print() { System.out.println(a, b); package taxonomy has the following classes class Panda extends Bear { void print() { System.out.println(a, b); class Fish { Bear cuddly = new Bear(); void print() { System.out.println(cuddly.a, cuddly.b); In the following table, place an X in each box in which member functions of that class may access the indicated variable (i.e., you are using the X's to indicate the classes in which a and b are visible). class a b Bear Dog Grizzly Panda Fish 19. (4 points) Write the java command to execute the file Zoo.java using the following assumptions: Zoo.java is in the animal package The animal directory is stored in a directory named /Users/bvz/exam1. I am in /Users/smiley/homework1 when I try to execute Zoo.java (the name of the directory is irrelevant--what is relevant is that I am not in either the animal directory or its parent directory). Assume that Zoo.java does not reference any classes other than the ones in animal. 9 of 10 3/4/19, 12:15 PM

10 20. (5 points) Why should you use C++'s exception handling mechanism (assume you catch the exception in main and then return) rather than the exit() statement to terminate a program when a catastrophic error occurs in a deeply nested function? Your answer must be 5 sentences or less. 10 of 10 3/4/19, 12:15 PM