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CMSC
Spring 2008
Midterm #2 Key
First Name: _______________________
Last Name: _______________________
Student ID: _______________________
Discussion TA: ______________________
Discussion Time: _____________________
I pledge on my honor that I have not given or received any unauthorized assistance on this
examination.
Your signature: _____________________________________________________________
General Rules (Read):
This exam is closed book and closed notes.
If you have a question, please raise your hand.
Total point value is 100 points.
The short answer questions are not essay questions. Strive to answer them in 1 or 2
sentences. Longer answers are not necessary and are discouraged.
WRITE NEATLY. If we cannot understand your answer, we will not grade it (i.e., 0
credit).
PUNT RULE:. For any question, you may write PUNT, and you will get ¼ of the points
for the question (rounded down). If you feel totally lost on a question, you are encouraged
to punt rather than waste time writing down an incorrect answer in hopes of getting some
partial credit.
Honors section questions only count for credit for students in the honors section.
Grader Use Only:
#1 Software Engineering (30 pts)
#2 GUI/Inner Classes (10 pts)
#3 Threads (15 pts)
#4 Graphs (25 pts)
Trees
(20 pts)
Honors (10 pts)
Problem 1 (30 pts) Software Engineering
a. (1 pt) Regression testing ensures functionality is not lost when software is bought & sold. F b. (1 pt) Pair-Programming is one of the characteristics associated with extreme programming. T c. (1 pt) Formal methods are mathematically-based techniques used for high-integrity systems. T d. (1 pt) We prefer inheritance over composition when designing a system. F e. (1 pt) Test coverage measures whether code is executed by some test case. T f. (1 pt) Omega testing can start once we have completed Alpha and Beta testing. F g. (1 pt) Good unit tests eliminate the need for integration tests. F h. (2 pts) The software life cycle is a sequence of essential operations necessary for producing quality software. Name two of those operations. Answer: Any two of Specification, Design, Selection of Algorithms, Coding and Debugging, Testing and Verification, Documentation and Support, Maintenance. i. (2 pt) In code that contains two if statements, what is the maximum number of flow paths through the code? Answer: 4 j. (2 pts): The Unified process model, the waterfall model, and extreme programming are three different software development methodologies. Order these, from most suitable to least suitable, for developing a totally new kind of application where the functionality required by the application isn’t well understood. Answer: Extreme, Unified, Waterfall k. (2 pts): Compare when/how testing is done in extreme programming, compared to the waterfall model. l. Answer: XP – testing done throughout the whole development process; waterfall at the end
Problem 2 (10 pts) GUI/Inner Class
1. (1 pt) JFrame and JPanel are considered containers. T 2. (1 pt) Inner classes can only access private components of the outer class. F 3. (3 pts) Briefly describe the three components associated with Model-View-Controller model? Answer: Model handles data (performs actual work), View lets user see what program is doing Controller controls what work the program is doing (1 pt) What is the Event Dispatching Thread? Answer: Thread where we schedule GUI processing 4. (4 pts) Rewrite the main method using an inner class named Handler rather than using an anonymous inner class. public class GUIExample { public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { new GUIExample(); } }); } }
Answer:
public class GUIExample { public static class Handler implements Runnable { public void run() { new GUIExample(); } } public static void main(String[] args) { javax.swing.SwingUtilities. invokeLater (new Handler()); } }
Problem 3 (15 pts) Threads
1. (1 pt) A thread (child) created by another thread (parent) will die immediately after the parent dies. F 2. (1 pt) If multiple threads are reading a shared field they should use synchronization, even if no other thread is updating the field. F 3. (1 pt) Any lock object used to protect a critical section must always be stored in a static field. F 4. (1 pt) A thread can only hold a maximum of two locks at a time. F 5. (1 pt) If a thread holds a lock on an object x , that prevents other threads from changing any fields of x. F 6. (1 pt) We can use a join method call to make a thread wait for another thread to complete execution. T 7. (1 pt) Each thread has its own stack but it shares the heap with other threads. T 8. (2 pts) Assume t1 and t2 are two thread objects. Circle the ones in which a data race could be possible between threads t1 and t2 (circle one or both, as appropriate; if neither, write NEITHER). Sequence1 t1.start(); t2.start(); t1.join(); t2.join(); Sequence2 t1.start(); t1.join(); t2.start(); t2.join(); 9. (6 pts) Implement the delayedShutdown method in the following class. public class Shutdown { /** Print msg and shut down JVM / public static void shutdownNow(String msg) { System.out.println(msg); System.exit(1); // cause entire JVM to shut down } /* * Method should create and start a thread so that after sleeping * for the number of seconds provided, the method shutdownNow * is invoked with the supplied msg. * This method invocation should return immediately, not waiting the * for the shutdown to occur. */ public static void delayedShutdown(int seconds, String msg) { Answer 1 (implements Runnable) public class Shutdown implements Runnable { private int secs; private String msg; public static void shutdownNow(String msg) { System. out .println(msg); System. exit (1); // cause entire JVM to shut down } public static void delayedShutdown(int seconds, String msg) { Thread t = new Thread(new Shutdown(seconds, msg)); t.start(); } public Shutdown(int secs, String msg) { this.secs = secs; this.msg = msg; }
Problem 4 (25 pts) Graphs
- (8 pts) Heaps a. Draw the heap that will result from adding 11 to the above heap. Answer: b. Draw the heap that will result from removing 10 from the original heap. Answer:
- (3 pts) What is the post order traversal for the following binary tree?
Answer: ACEDB
(8 pts) BFS/DFS a. Given two different possible orders in which the nodes of this graph could be visited in performing a Breadth First Search (BFS) starting at vertex A. Answer(s): Any two of: ABQCYRW, ABQCRYW, AQBCYRW, AQBCRYW b. Given two different possible orders in which the nodes of this graph could be visited in performing a Depth First Search (DFS) search starting at vertex A. Answer(s): Any two of : ABCRWQY, ABCYWQR, AQCRWBY, AQCYWBR
- (6 pts) Dijkstra’s C D A E B
Problem 5 (20 pts) Binary Trees
Implement the method below based on the following Java class definitions. You may not add any instance variables or static variables either class, and you may not add any methods to the Node class. You will need to add a helper recursive function to the BinaryTree class (that takes a Node as a parameter). Non-recursive solutions will receive zero credit. public class BinaryTree { private static class Node { private T data; private Node left, right; private Node(T data) { this.data = data;} } public boolean isFull() { // YOU MUST IMPLEMENT THIS METHOD } private Node root; } Implement the method called isFull() that returns true if a binary tree is a full tree and false otherwise. A binary tree is full if and only if every node in the tree has either zero or two children.
Answer:
public boolean isFull() { return isFullAux(root); } private boolean isFullAux(Node ra) { if (ra == null) return true; if (ra.left == null && ra.right == null) return true; if (ra.left != null && ra.right != null) return isFullAux(ra.left) && isFullAux(ra.right); return false; }
