Question 2. [12 points] Write a sequence of statements that does the following:

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1 CS 201, Fall 2008 Oct 6th Exam 1 Name: Question 1. [6 points] What output is printed by the following program (which begins on the left and continues on the right)? public class Q1 { public static void f(int x) { x++; System.out.println(x); public static void main(string[] a){ int x = 4; f(x); f(x); Question 2. [12 points] Write a sequence of statements that does the following: 1. Asks the user for his/her name, reading the user s response from the keyboard 2. Asks the user for his/her age, reading the user s response from the keyboard 3. Prints a message indicating whether or not his/her age is prime Example run (user input is underlined): Your name? Alice Your age, Alice? 31 Alice, your age is prime Hint: for an integer n to be prime you must show that there is no integer in the range 2..n/2 that evenly divides n.

2 Question 3. [10 points] Write a static method called reversestring that takes a String as a parameter, and returns another String which reverses the characters in the parameter string. Hints: the charat(int) method of the String class gets a character at a given index in the string, the length() method returns the length of the string, and the + (plus) operator can be used to concatenate a string and a character to form a new string. Example test: String s = "Runcible spoon"; String rs = reversestring(s); System.out.println(rs); // prints "noops elbicnur" Question 4. [6 points] (a) What output is printed by the following code snippet? String s1 = "Frotz"; String s2 = ""; char[] c = new char[]{ F, r, o, t, z ; for (int i = 0; i < c.length; i++) { s2 = s2 + c[i]; System.out.println(s1 == s2); System.out.println(s1.equals(s2)); (b) Briefly explain why the snippet produced the output it produced.

3 Question 5. [10 points] Write a static method called numuppercase which counts the number of values in an array of char elements that are upper-case letters (in the range A Z ), returning the count as the method s return value. Example test: char[] carr = new char[]{ B, o, y,, H, o, w, d, y ; System.out.println(numUpperCase(cArr)); // prints "2" Question 6. [12 points] Define a class called Bar which prints a horizontal bar of a specified length using = (equals) characters. The length of the bar is specified by passing an integer value to Bar s constructor. The class s print() method prints the bar using System.out. An example code snippet (left) and its output (right): Bar b1 = new Bar(15); Bar b2 = new Bar(31); =============== =============================== b1.print(); b2.print();

4 Question 7. [12 points] Consider the following two interfaces: public interface Vehicle { public double getmaxspeed(); public interface Animal { public int getnumberoflegs(); Also consider the following static methods: public static void zoom(vehicle v) { System.out.println( "Top speed of " + v.getmaxspeed()); public static void countlegs(animal a) { System.out.println( "The animal has " + a.getnumberoflegs() + " legs"); Write a class called Horse such that the following sequence of statements is legal and produces the output indicated by the comments: Horse h = new Horse(); zoom(h); // prints "Top speed of 25.0" countlegs(h); // prints "The animal has 4 legs"

5 Question 8. [12 points] Write a generic method, called swap, which swaps the elements at two given indices in an ArrayList. Assume that your method will be defined in a clas called Q8. Your method must allow elements of any ArrayList to be swapped, regardless of its element type. Example JUnit test (which begins on the left and continues on the right): public class Q8Test extends TestCase{ private ArrayList<String> s; protected void setup() { s = new ArrayList<String>(); s.add("alice"); // adds element 0 s.add("bob"); // adds element 1 public void testswap() { Q8.swap(s, 0, 1); assertequals("bob", s.get(0)); assertequals("alice", s.get(1)); Hint: use the get(int) and set(int, E) methods of ArrayList to get and set element values. Question 9. [8 points] The Liskov Subsitution Principle (LSP) states: Anywhere in a program an instance of a superclass is expected, an instance of a subclass may be used. One of the questions on this exam shows a code snippet that makes use of the Liskov Substitution Principle. State which one, and explain precisely what code in the code snippet employs the LSP.

6 Question 10. [12 points] Define a class called ReverseStringComparator which implements a reverse string comparator. When an array of n strings is sorted using the reverse string comparator, element 0 should contain the greatest (last) string, and the element n 1 should contain the least (first) string. Your class must implement the Comparator<String> interface, and define the method. public int compare(string left, String right) Example JUnit test: public class Q10Test extends TestCase{ private ArrayList<String> s; protected void setup() { s = new ArrayList<String>(); s.add("alice"); // adds element 0 s.add("carl"); // adds element 1 s.add("bob"); // adds element 2 public void testreversesort() { // sort the array list using the // reverse string comparator Collections.sort(s, new ReverseStringComparator()); assertequals("carl", s.get(0)); assertequals("bob", s.get(1)); assertequals("alice", s.get(2)); Note that the Collections.sort method is much like Arrays.sort, except that it sorts an ArrayList (or other collection object), rather than an array.