Programming and Problem Solving with Java

CASE STUDY

504

Data Representation:The exam answers are an ordered collection of T’s and F’s. An

array is the obvious choice for holding the T’s and F’s. The index of an individual answer

is the question number minus one. Now we are ready to design the algorithms for the

two classes.

Responsibility Algorithms for AnswerSheet: We have forgotten something. How do we

know how many questions were asked on this exam? We must know this information

to instantiate the objects of class AnswerSheet. The user could enter it from the keyboard

as an event, or the user could enter the number of questions on the file, on the line im-

mediately before the key. Because this application does not need the user to be present

to enter any other data, putting the number of questions on the data file is the better

choice. The responsibility for reading this value should be in the driver.

There is another problem: A student’s answer sheet contains a name that is printed

along with the number correct. The key doesn’t have a name to be read. We can have

two input methods, one that reads a name and the sequence of T’s and F’s and one that

reads just the T’s and F’s. Another alternative is to have the instructor supply “Answer

Key” for the name. This second alternative is simpler because it requires only one input

method. Here, then, is what the input file would look like.

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Answer Key

TFTFTFTFTTTFFFT

Joe Jones

TFTFTFTFTTTFFTT

Janet Jerome

TFTFTFTFTTTFFFF

Jeff Jubilee

TFTFTFTFTTTFFFT

...

Answer Sheet (int numQuestions)

Create responses as an array of numQuestions characters

Class Name: GradeExams Superclass: Object Subclasses:

Responsibilities Collaborations

Prepare files for input

Prepare files for otput FilerWriter, PrintWriter

FileReader, BufferedReader

Get key AnswerSheet

Process exams

Close files

AnswerSheet

None