Computer Science 15-110, Spring 2010
Recitation for Week #2

1. Quizlet (quiz #1, part 1)
2. Enabling Assertions
3. CA-Directed Lab
   1. "Writing Static Methods" Review
      1. square
      2. printSquare
      3. isPositive
      4. areaUnderLine
      5. isEvenPositive
      6. minSquared and testMinSquared
      7. isOdd and testIsOdd
4. Student-Directed (Collaborative) Lab
   1. triangleArea
   2. enoughEggCartons
   3. reverseNumber
   4. isPalindromeNumber
   5. flagOfMauritania
   6. More Flags (time permitting)

1. Quizlet (quiz #1, part 1)
   See quiz1, part 1.
    
2. Enabling Assertions
   Review the "Enabling Assertions" section from the class notes, especially the part on Enabling Assertions in DrJava.
    
3. CA-Directed Lab
   1. "Writing Static Methods" Review
      To be sure we cover all of the methods included in the class notes on "Writing Static Methods", in recitation, review the following methods in these notes:
      1. square
         
           public static int square(int n) {
             return n*n;
           }
          
      2. printSquare
         
           public static void printSquare(int x) {
             System.out.println(x + "^2 = " + square(x));
           }
          
      3. isPositive
         
           public static boolean isPositive(int x) {
             return (x > 0);
           }
          
      4. areaUnderLine
         
           // This method computes the area in the first quadrant under
           // the line y=mx+b.  It assumes m is negative and b is positive,
           // so we in fact have a triangle in the first quadrant.
           public static int areaUnderLine(int m, int b) {
             // The x-intercept of y=mx+b is where y=0, so
             // mx+b=0, so x=-b/m
             int width = -b/m;
             // b is the y-intercept
             int height = b;
             // now we have the width and height of the right triangle
             // under the line in the first quadrant, so...
             return width*height/2;
           }
          
      5. isEvenPositive
         
           public static boolean isEvenPositive(int x) {
             boolean isEven = ((x % 2) == 0);
             boolean isPositive = (x > 0);
             return (isEven && isPositive);
           }
          
      6. minSquared and testMinSquared
         
         class MyCode {
           public static int minSquared(int x, int y) {
             int min = Math.min(x, y);
             return (min * min);
           }
         
           public static void testMinSquared() {
             System.out.print("Testing minSquared... ");
             assert(minSquared(2,3) == 4);
             assert(minSquared(3,2) == 4);
             System.out.println("Passed all tests!");
           }
         
           public static void main(String[] args) {
             // remember to enable assertions (with -ea flag)
             testMinSquared();
           }
         }
          
      7. isOdd and testIsOdd
         
         class MyCode {
           public static boolean isOdd(int x) {
             return ((x % 2) == 1); // ERROR: This contains a bug!
           }
         
           public static void testIsOdd() {
             System.out.print("Testing isOdd... ");
             assert(!isOdd(2));
             assert(isOdd(1));
             assert(!isOdd(0));
             assert(isOdd(-1));  // ERROR: This assertion will fail!
             assert(!isOdd(-2));
             System.out.println("Passed all tests!");
           }
         
           public static void main(String[] args) {
             testIsOdd();
           }
         }
          
4. Student-Directed (Collaborative) Lab
   1. triangleArea
      Write a method, triangleArea, that takes two integers -- a width and height, both assumed to be non-negative -- and returns the (integer) area of the corresponding triangle.  Include a test method.
       
   2. enoughEggCartons
      Write a method, enoughEggCartons, that takes two integers -- the number of eggs and the number of egg cartons, both assumed to be non-negative -- and returns true if there are enough egg cartons to hold that many eggs and false otherwise.  Include a test method.
       
   3. reverseNumber
      Write a method, reverseNumber, that takes a 4-digit integer, assumed to be positive, and returns the number in reverse.  So a call to reverseNumber(2468) returns 8642.  Include a test method.
       
   4. isPalindromeNumber
      Write a method, isPalindromeNumber, that takes a 4-digit number, assumed to be positive, and returns true if that number is a palindrome (same forwards as backwards), and false otherwise.  While there are several ways to do this, your method must call the reverseNumber method you just called and then use the result of that method call to check if the original number is in fact a palindrome.  Include a test method.
       
   5. flagOfMauritania
      Following the usual guidelines, write a program that displays the flag of Mauritania.  Replace the star with a circle.
             Mauritania
               (larger image with details)
       
   6. More Flags (time permitting)
      As time permits, draw more flags (replacing stars with circles) from the CIA Flags of the World page.

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