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CSC 205 Programming II

CSC 205 Programming II. Lecture 22 Carwash Simulation. Recap: Queue. A queue is an ordered, linear data structure New items are added at the rear end Items are removed from the front end It’s a “ first-in, first-out ” (FIFO) structure Queue operations

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CSC 205 Programming II

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  1. CSC 205Programming II Lecture 22 Carwash Simulation

  2. Recap: Queue • A queue is an ordered, linear data structure • New items are added at the rear end • Items are removed from the front end • It’s a “first-in, first-out” (FIFO) structure • Queue operations • Enqueue – add an item to the rear end • Dequeue – remove the front item • Peek – get the content of the top item

  3. Carwash Simulation

  4. The Problem • A carwash station can wash one car at a time • Time needed to wash a car is measured in seconds • Cars may arrive at any given second • A probability can be assumed • Cars arrived when the washer is busy have to wait in line • First-come, first-served • The goal: find out the average waiting time for a given period of time (in seconds)

  5. Program Specification • Input • Time needed to wash one car • The probability that a new customer arrives at any given second • The total length of time to be simulated • Output • Car arrival and leaving history • Number of customers serviced • Average time that a customer spent in line during the simulation

  6. Design • Objects relevant to the carwash problem • A collection of cars: CarQueue • Car • Washer • Other objects used in the simulation • Random arrival time generator: BooleanSource • Average time calculator: Averager • The application driver class: CarWashApp

  7. Detailed Design • Key design concept • Determine which properties of a real-world object are relevant to the problem at hand • Car • Arrival timestamp • Sequence number • CarQueue • A linked list object is used as a queue • Three operations • enqueue, dequeue, isEmpty

  8. Detailed Design – continued • Washer • Variables • Time (in seconds) needed to wash a car • Time left to finish washing the current car • Operations • Start washing • set washTimeLeft to secondsForWash • Reduce remaining time • Decrement washTimeLeft if it is not zero • Test if the washer is busy • It’s busy if washTimeLeft is greater than zero

  9. Detailed Design – continued • BooleanSource • Variable: probability • Operation: query • returns true only if Math.random() < probability • Averager • Variables • A count and a sum • Operations • addNumber: update both count and sum • howManyNumbers: return count • average: return sum/count

  10. Car Wash Application • carWashSimulate • Three parameters • Time needed to wash a car • Probability • Total time • Echo input parameters • Validate parameters • Processing car washing with a loop • Output results

  11. Car Wash Application • Within the loop • Check if a new car arrives • Check whether we can start washing another car • That is if washer is not busy, and • The queue is not empty • Reduce the remaining time during washing a car

  12. Sample Simulation C:\courses\CSC205\labs\carwash>java CarWashApp2 Seconds to wash one car: 1000 Probability of customer arrival during a second: 0.0010 Total simulation seconds: 5000 Car Arrived Left Waited 1 470 470 0 2 1412 1470 58 3 1580 2470 890 4 2900 3470 570 5 3559 4470 911 Customers served: 5 Average wait: 485.8 sec

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