Computing Assignment 7: Arrays

Assigned: Tuesday, March 3, 1998
Due: Thursday, March 12, 1998

Purpose: In this assignment, you will attempt to develop more complex programs that take advantage of Java's arrays. Hopefully, you will also gain a better understanding of for loops.

Warning: At times, Java is incredibly verbose. At other times, it is confusingly terse. Why do we do things the way we do? Because the designers decided that we whould. (I.e., "it's just the way things are").

Background

Recall that there are three basic steps to building a Java program (assuming that SamR has helped you make the change that allows this shorthand).

• You must enter and save the program in Xemacs.
• You must compile (tranlsate) the program using
  jc Program.java
• You must then interpret (execute) the program using
  ji Program

Of course, when creating a program from scratch, you should begin by sketching the design of the program: what it does and how it does it.

The Beginning of a Program

Here are a template for a simple class that computes various aspects of a set of numbers and a program that uses that class. Note that not all of the methods in the first class are correctly defined.

Make a copy of the first program, save it as Computations.java, and compile it. Make a copy of the second program, save it is UseComputations.java, compile it, and execute it. Here are the commands you'll use

% jc Computations.java
% jc UseComputations.java
% ji UseComputations.java

See what happens when you change the values in the array. You might add values, delete values, or use different values. Note that after changing the values, you will need to recompile and reexecute the program.

Extend the Program

This program is missing definitions for a number of methods, including maximum, minimum, and average. Fill in the instructions for those methods. It is likely that the instructions will bear some similarity to those I used for sum.

Extra Credit

For extra credit, extend UseComputations.java to read in the array, rather than predefining it.

Turning it In

Email me your version of the program, using a sequence of commands like
% elm rebelsky < Computations.java
% elm rebelsky < UseComputations.java

Program Code

Computations.java

/**
 * Perform a series of computations (sum, minimum, maximum, average)
 * on an array of numbers.
 *
 * @author Samuel A. Rebelsky
 * @author YOUR NAME HERE
 * @version 1.1 of March 1998
 */
public class Computations
{
  // +---------+-----------------------------------------------------------
  // | Methods |
  // +---------+

  /**
   * Compute the average value in an array of numbers.
   */
  public double average(double[] stuff)
  {
    // The instructions for this method need to be filled in
    return 0;
  } // average(double[])

  /**
   * Compute the maximum value in an array of numbers.
   */
  public double maximum(double[] stuff)
  {
    // The instructions for this method need to be filled in
    return 0;
  } // maximum(double[])

  /**
   * Compute the minimum value in an array of numbers.
   */
  public double minimum(double[] stuff)
  {
    // The instructions for this method need to be filled in
    return 0;
  } // minimum(double[])

  /**
   * Compute the sum of values in an array of numbers.
   */
  public double sum(double[] stuff)
  {
    // The total of the values.  Initially 0, since we haven't
    // seen any values.
    double total = 0;
    // A counter to step through the array.
    int i;
    // Step through the array, updating the total as we go.
    for(i = 0; i < stuff.length; i = i + 1) {
      total = total + stuff[i];
    }
    // That's it, we're done.
    return total;
  } // sum(double[])

} // Computations

UseComputations.java

import rebelsky.io.SimpleOutput;	// We'll be printing results
import Computations;			// We'll be computing

/**
 * Perform a series of computations (sum, minimum, maximum, average)
 * on an array of numbers.  To change the array of numbers, you'll need
 * to change the code for this program and recompile.
 *
 * @author Samuel A. Rebelsky
 * @author YOUR NAME HERE
 * @version 1.1 of March 1998
 */
public class UseComputations
{
  // +------+--------------------------------------------------------------
  // | Main |
  // +------+

  public static void main(String[] args)
  {
    // Prepare for writing output
    SimpleOutput out = new SimpleOutput();
    // Create an array to compute with
    double[] values = { 3.2, 4.4, 5, 2, 1, 9, 0, -4 };
    // Create an object of this type so that we can do some 
    // computations.
    Computations comp = new Computations();

    // Print the array.
    out.print("Working with the array: ");
    out.println(values);

    // Print the various computed values
    out.print("The average of those values is: ");
    out.println(comp.average(values));
    out.print("The largest of those values is: ");
    out.println(comp.maximum(values));
    out.print("The smallest of those values is: ");
    out.println(comp.minimum(values));
    out.print("The sum of those values is: ");
    out.println(comp.sum(values));

    // That's it.  We're done.
    System.exit(0);
  } // main

} // UseComputations