CAR WASH SIMULATION PROJECT
By Autumn C. Spaulding with Alyce Brady • Edited by Sandino Vargas-Pérez

PROBLEM DESCRIPTION

Construct a simulation of a car wash to determine the average waiting time during a typical day (9 am to 7 pm) using different types of equipment. See the Car Wash Design Exercise for a full description of the Car Wash Simulation we wish to develop.

In addition to implementing the simulation, write a report for the owners of the Squeaky Clean Car Wash that presents an analysis of your results. (See the Analysis section below for full details.)

You may wish to develop your own design for this program, or you may use the design presented in the Car Wash Design Case Study.

Implementation

Implement the Car Wash Simulation program. A reasonable set of classes for the problem would be:

• CarWashApplication: Contains the main method.
• Random: Generates random numbers (java.util.Random).
• Car: Represents a car (stores the time when the car arrived at the car wash).
• K_LLQueue: Stores cars that are currently waiting. (This class from the Queues Mini-Lab #3 provides a cleaner implementation of the Queue abstract data type than do the standard Java classes that implement the java.util.Queue interface.)
• Bay: Keeps track of whether or not the car wash bay is available and how much longer the current wash will last.
• CarWashSimulation: Controls the simulation (contains a loop like the one described in the pseudo-code below). Your simulation should re-evaluate the state of the Squeaky Clean Car Wash every minute.

Test-Driven, Iterative Development

Develop and test your program in small increments. For example, you might proceed through the following steps:

Step 1: Construct Car objects and use a queue

Create a Car class that keeps track of a car's arrival time. Have your main method loop a number of times (e.g., 20 times). In each step, print a timestamp and implement the random arrival of a car, putting cars in a queue. Test the queue by stepping through it at the end, printing the arrival time of each car. Your output at this point might look something like:
  time step 0: A car arrived.
  time step 1: No car arrived.
  time step 2: No car arrived.
  time step 3: A car arrived.
  time step 4: A car arrived.
  ...
  Cars in queue:
  Car arrived at time step 0.
  Car arrived at time step 3.
  Car arrived at time step 4.

(You may wish to use the Debug class for printing debugging information.)

Step 2: Develop and test the Bay class

Create a Bay class that tracks a car's progress through the bay, noting how many minutes of delay until the bay is available. When no car is in the bay, the delay is 0. (Tip: Pass the length of a car wash as a parameter so that you can experiment with times other than 3 minutes later.)

You might want to modify your main method to loop through several time steps, but have a car arrive in only one pre-determined step. In each time step, report how long it will be before the car bay is available. For example, you might have:
  time step 0: No car arrived. Bay available in 0 minutes.
  time step 1: A car arrived. Bay available in 3 minutes.
  time step 2: No car arrived. Bay available in 2 minutes.
  time step 3: No car arrived. Bay available in 1 minutes.
  time step 4: No car arrived. Bay available in 0 minutes.

Step 3: Develop and test the CarWashSimulation class

Implement the step method in the simulation class to handle a single minute when the car wash is open. Have the main function run the simulation for a small number of times (for example, 10 minutes) to test your code (especially the calculation of total wait time) on simple cases before trying to simulate an entire day. Update the main function to print the total number of cars serviced, the total wait time for all the cars, and the average wait time.

Step 4: Complete the project

Once the simulation's step method seems to be running correctly, update it to handle cars that are still in the queue when the car wash closes and any other aspects of the original problem description that have not yet been implemented.

ANALYSIS

Since providing the original problem specification, the owners of the Squeaky Clean Car Wash have asked for some additional information:

• They would like to know the wait times for their current equipment (4 minutes/wash) as well as the proposed new equipment (3 minutes/wash) for a typical week (7 days, 10 hours per day).
• They really don't want their customers to have to wait more than ten minutes for a car wash, and would like to know how often such long waits happen in a typical week.

To answer these questions, simulate one week (7 days) of operation. Use your results to write a report that shows the average wait time and the number of cars that would have waited more than ten minutes for each type of machine (four-minute and three-minute wash) for each day in the 7-day period. For example, your output might include a table like the one below, along with a paragraph of explanation and conclusions. (Note that the numbers in the table below are completely made up, and should not be used to validate your results.)

Optional Enhancement

Another alternative that the car wash owners are considering is to add a second bay similar to the one they have now, with a single line that serves them both. Customers would wait in the one line and enter the next available bay to get their car washed. What changes would you have to make to the main program to make this work? What changes will you have to make to your other classes?

Modify your program to handle multiple bays, and update your report to show what the results of having two bays would be. Run your analysis on the new setup. Could they handle twice as many cars with the same average wait time they have now?

Submit your completed program through Kit, under Car Wash Simulation Project.

Have fun! And if you have any questions remember I am available through email, Teams, and my office hours. And don't forget the Collaboration Center, which is a great place to work and ask questions too!