Homework 2 (HW2) Solution

Please read the instructions carefully before submitting your work.










Note: Solve all problems and upload your answers to Moodle. Whenever you write solutions on paper, you need to scan it and upload the file(s).




Note: user stands for your login ID on polaris.clarkson.edu. This should be the exact same as your CU ID.




Note: Make sure any code you write works on polaris.clarkson.edu before uploading your files. You may lose many points if your code doesn't even compile.




Note: Please do not upload any executable or intermediate files as answers to problems, unless specifically asked to do so.













Note: Read Chapters 1 through 4 of the textbook and answer the questions that follow.
















Total points: 40








































2









Problem 1 (10 points)




Study Student.java and studentAPI.txt (these were discussed in class).




Modify function updateCourseGrades in class Student so that if any of the elements inside the argument are negative, it throws an InvalidGradeException. You should define InvalidGradeException as a subtype of Java's RuntimeException class. Note that updateCourseGrades accepts an array of grades for a student, and adds them to the existing list of grades for this student; it does not remove or overwrite any previous point grade.







Then, write a client class UseStudent that attempts to do the following:

--create two Student objects named ms1 and ms2; ms2 is to be initialized with grades {10.0, 5, 3.5, 6, 4}

--update grades of ms1 with values {10.5, 40}

--update grades of ms2 with these values {8, -6.5, 20.0}




--print out the total number of students by calling the appropriate function in class Student




--list the grades for students ms1 and ms2 by calling the appropriate function; note that the intention of the client is that ms1 should have grades {10.5, 40} and ms2 should have grades {10.0, 5, 3.5, 6, 4, 8, -6.5, 20.0}
















Deliverable: Upload UseStudent.java, your (modified) version of Student.java, and the exception class source file to Moodle.































3



Problem 2 (10 points)




Write a class BasicNum that contains a function called gcd with the following header (shown along with specifications):




//@ requires: ! (x==0 && y == 0)




//@ signals_only: ZeroException (a user-defined, checked




exception)




//@ ensures: throws ZeroException if both x and y are zero,




//@ otherwise returns the gcd of x and y.




public static int gcd(int x, int y) throws ZeroException










You will need to define the ZeroException class.




The method gcd computes the greatest common divisor (GCD) of two numbers. The GCD of two numbers, both of which cannot simultaneously be zero, is the greatest positive number that divides both evenly. For example GCD(2, 4) is 2; GCD (2, 9) is 1, GCD(75, 50) is 25, GCD(8, 1) is 1, GCD(3, 0) = 3, GCD(0, 8) = 8.




Note that GCD(a, b) = GCD(b, a), and GCD(a, 0) = a.




Write a client class CheckGCD that tests your implementation (BasicNum.gcd ) by calling it with all the 6 pairs of numbers shown above, and an additional 4 times (so a total of 10 calls).



















Deliverable: Upload BasicNum.java, ZeroException.java and CheckGCD.java to Moodle.



















4



Problem 3 (10 points)




Write a class ArrSum containing a standalone procedure sum with the following header:




public static int sum(int[] a)




sum takes an integer array as an argument, and returns the sum of all array elements back to the caller.




Write appropriate specifications (precondition, postcondition, and frame properties using assignable/modifies) for sum that describe its behavior to all potential clients. Also provide an implementation of sum (that meets your specifications).




Write a driver class TestSum with at least 3 different calls to sum.










Note: You must explicitly write all relevant specifications, i.e. the precondition, postcondition, and the frame condition. For example, even if the precondition for your implementation is 'true', you must have a requires clause that says this.
















Deliverable: Upload the file with the source for ArrSum and also the client source/driver file to Moodle.

















































5



Problem 4 (10 points)




Solve problem 4.3 from the textbook. Write the solution in a plain text file called user_hw2_prob4.txt.










Deliverable: Upload user_hw2_prob4.txt to Moodle.






















End