54-283 PC II - Chapter 2 - Programming Assignment  Implement and Test the Statistician Class

The Assignment:

You will complete the implementation and test a small class called Statistician, which is similar to some of the small classes in Chapter 2 of the text.

Purposes:

Ensure that you can write a small class that meets a precise specification.

Give you experience in using a test program to track down bugs in a class's implementation.

Before Starting:

Read all of Chapter 2.

Know how to compile and run java programs on your system.

File that you must complete:

• Statistican.java

Other files that you may find helpful:

1. StatTest.java: A simple interactive test program.
2. Statistician.html: A detailed discussion of the specification.
3. statexam.java:  A grading program to indicate what your program might get.

Hand in:

1. A diskette with a folder clearly labeled Lab2 which contains my program StatTest.java and your Statisitican.java
2. A printout of the code for Statistician.Java

 The Statistician Class 
Discussion of the Assignment

You will implement a new class called Statistician, the specification (most of which is written for you) and the implementations for the class specification which you must finish . The Statistician is a class that is designed to keep track of simple statistics about a sequence of real numbers. There are two member methods that you should understand at an informal level before you proceed any further. The prototypes for these two functions are shown here as part of the Statistician class declaration:As indicated above,

public double mean( )
   {
      // The student's code will replace this return statement:
      return 0.0;
   }

public void next(double number)
{
}

Hints

The Private Member Variables

Carefully read the class definition in Statistician.java.  Notice how the private member variables are being used to keep track of information about the Statistician's sequence of numbers. The Statistician does NOT keep track of all the numbers in the sequence. There is no need to do so, and trying to do so can get you into trouble. Instead, it keeps track of only the information that is relevant to its member functions: How many numbers have been seen? What is the sum of those numbers? If you have seen at least one number, then what are the smallest and largest numbers that you've seen so far? These four items should be your only private member variables.


Be careful about how you set the private member variable that keeps track of the smallest number. My suggestion is that you do NOT have the constructor initialize this member variables (because when the constructor does its work, there have not yet been any numbers, so there is no smallest number). But part of the work of the "next" function is to correctly maintain the private member variables. This means that the first time that the next function is called, it should set the private member variable that keeps track of smallest values. Later, if next is called again with a smaller number, then the next function will change the member variable that is keeping track of the smallest value. (You'll have a similar process for the member variable that's keeping track of the largest value).
 

Check Boundary Values

Make sure that your addAtEnd method  works correctly when the arguments are Statisticians with no numbers.

Check Preconditions

Your implementations should use  throw  function to check preconditions of all functions.

Input and Output

Your implementations must NOT produce any output to System.out  nor expect any input from InputStream. All the interaction with the class methods occurs through their parameters.

Implement and Test Small Pieces

Don't tackle to whole project at once. Start by implementing what you can, using "stubs" for the harder functions. A "stub" is the implementation of a function with the lines of the body omitted. For example:

public Statistician( )


{
    // Student implementation.

}

A first implementation might have only:

• The constructor
• A simple version of next that increments the private member variable to keep track of how many numbers have been seen
• The length function

Even with just stubs, your Statistician.java  file will correctly compile and link with the interactive test program, StatTest.java..

---

to accompany Data Structures and Other Objects Java

by Michael Main
ISBN 0-201-35744-5, 1999