Problem

You are an employer on the software team of Bikers Forever, a bicycle company. The software team uses Java and the knowledge of the Java SDK to write programs for Biker Forever. You are a great COMP 1010 student so you already have an idea of writing in Java, so in breathless anticipation, you await your next assignment from the head of the software team :)

You arrive at your desk on Monday morning and open your email in-box (as usual) to see this message from the head:

Hi <insert name here>,

I need you to write a program that allows customers who visit the Bicycle Forever to calculate the speed of their bicycles. One of the members of the team stumbled on the formula to calculate cycling speed, and knowing you are just itching for an assignment, I thought of you straightaway to implement the formula. The program description and the formula is below:

Program Description

1. The program will prompt the user to input
   • The RPM (rotations per minute) of the bicycle
   • The number of teeth in the rear gear
2. The program will also store as constants the number of teeth in the front gear and the diameter of the bicycle wheel. Assume the number of front teeth to be 45 and the diameter to be 70cm always.

Formula

1. Before you calculate the speed, you must first calculate the meters of development. This is the length in meters covered by each rotation of the wheel of the bicycle. Meters of development (mdev, as we'll call them) are calculated this way:

   mdev = circumference[m] * (number front teeth / number rear teeth) 
   

2. Finally, now that we have the mdev we can calculate the speed:

   speed = mdev * rpm * 60/1000 //Note that 60/1000 helps to calculate the speed in kilometers per hour
   

Output

To display your results, assuming a customer inputs 75 for RPM and 20 for rear teeth, the output will be displayed this way:

You have entered 75 RPM and 20 rear teeth.
Meters of development: 4.948008429403924
Speed [km/hour]: 22.266037932317655

Programmed by Bicycle Forever
Date: September 18, 2008
*** End of Processing ***

Thanks!, <insert name here>, I am confident you will do a great job.
The Boss

Cycling Speed

Solution

To program our solution, we will go through 4 steps:

1. Identify and declare all variables and constants
2. Store user input on bicycle information
3. Perform the calculations
4. Output the results

In addition, we will be sure to comment through out our code, and follow correct programming standards as stated in [1]

Identify and declare all variables and constants

Based on The Boss's email to you, and the description of the program and formula, we can easily identify all the variables and constants important to the solution.
NOTE: some of these variables are dependent on the others.

CONSTANTS:

• The number of front wheel teeth - assumed to be 45 everytime
• The diameter of the wheel - assumed to be 70cm everytime

Declaration of Constants
When declaring constants, we use the keyword final. This ensures that whether it is an int, double, string or any other data type, if it is a final int for example, it cannot be changed throughout the code.

As the number of front wheel teeth is a number, we will declare it using "final int"

final int FRONT_TEETH = 45;

We also know the constant for the diameter is 70cm every-time. However, the diameter is not used in the calculations. Rather, the circumference is used to calculate the meters of development.

So what should we do???

It's simple! Going back to your high school days you know that the Circumference of a circle (wheel) = 3.14 (pi) * the diameter.

• Pi in Java has been provided for us through Math.PI
• We also want to make sure we divide by 100.0 because our diameter is in centimeters right now as opposed to the meters we need to calculate the meters of development (if you remember!)
• And finally, our constant will be a "final int double" to represent the circumference. We declare and calculate the circumference right away since we already know the diameter and we use a double to accommodate the decimal spaces

Therefore our declaration becomes:

final int double WHEEL_CIRCUMFERENCE = (70 * Math.PI)/100.0;

Now that we have our constants, let go ahead to declare the rest of the variables we will need based on the formula. We will also include a string variable to store our user's input.

int rpm;
int rearTeeth;
double mdev; //a double because it will contain decimal spaces because of the circumference
double speed;
String input;

Store user input on bicycle information

In order to retrieve user input, we will be using the class JOptionPane. We are able to call this class and its methods when we type in "import javax.swing.*;" at the top of our program. Future computer science courses will explain what the import</import> statement does.

How JOptionPane works: JOptionPane has an InputDialog method which shows a dialog box and accepts input typed into that box. This input can then be stored in strings. What we will do in this case, is store the user input into strings and parse (convert) them to integers using Integer.parseInt.

How Integer.parseInt works: Integer.parseInt accepts a string and converts it to an int. The string however must contain numbers only or bad things happen :)

Below is our storage of input and conversion to actual integers.

input = JOptionPane.showInputDialog ("Enter rpms.");
rpm = Integer.parseInt(input);

input = JOptionPane.showInputDialog ("Enter number of teeth on rear gear.");
rearTeeth = Integer.parseInt(input);

mdev = WHEEL_CIRCUM * (FRONT_TEETH / (double)  rearTeeth);

speed = mdev * rpm; 				//speed in meters per minute
speed = speed * (60.0 / 1000); 			//speed in km per hour

int digit1;
int digit2;

digit1 = (isbn % 10);
int total = digit1 * 9;
isbn = isbn / 10;

digit2 = (isbn % 10);
total = total + digit2 * 8;
isbn = isbn / 10;

int digit;

digit = (isbn % 10);
int total = digit * 9;
isbn = isbn / 10;

digit = (isbn % 10);
total = total + digit * 8;
isbn = isbn / 10;

int isbn = Temp;

isbn = Integer.parseInt(temp);

Code

Solution Code

import javax.swing.*;
import java.text.SimpleDateFormat;
import java.util.Calendar;

/**
 * calculate the speed of a bicycle
 *
 * Bicycle Forever
 * @author:     <insert name here>
 * @version:    2011-March
 */

public class BicycleSpeed {
    /**....................................................main<br>
     * PURPOSE: inputs RPM and Number of Teeth and output speed
     */
    public static void main (String [] args) {

        //constants
        final int FRONT_TEETH = 45;
        final double WHEEL_CIRCUM = (70 * Math.PI)/100.0;  //diameter of wheels is 70cm; convert to circumference in meters 
 
        //variables
        String input;                        //inputorary input string
        int rpm ;                           //rpms
        int rearTeeth;                      //number teeth in rear gear
        double mdev ;                       //= circ [m] * (frontTeeth / REAR_TEETH)
        double speed;                       //= mdev * rpm (speed in meters per minute)

        //get input
        input = JOptionPane.showInputDialog ("Enter rpms.");
        rpm = Integer.parseInt(input);

        input = JOptionPane.showInputDialog ("Enter number of teeth on rear gear.");
		rearTeeth = Integer.parseInt(input);

        //confirm input
        System.out.println ("You have entered " + rpm + " rpms and " + rearTeeth + " rear teeth");

        //find meters of development
        mdev = WHEEL_CIRCUM * (FRONT_TEETH / (double)  rearTeeth);
        System.out.println("Meters of development: " + mdev);

        //find speed
        speed = mdev * rpm; 				//speed in meters per minute
        speed = speed * (60.0 / 1000); 			//speed in km per hour

        //BONUS
        Calendar calendar = Calendar.getInstance();
        SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");

        //output
        System.out.println("Speed [km/hour]: " + speed);

        System.out.println("\nProgrammed by Bicycle Forever");
        System.out.println("Date: " + dateFormat.format(calendar.getTime()));
        System.out.println ("*** End of Processing ***");
        System.exit(0);

        }//end main
}end class