Question

In Java, complete the following:

During the lunch hour, the ATM machine in a large office complex is in heavy demand. Customers complain that the waiting time is much too long. The local bank considering the addition of a second ATM machine. But first, the bank needs a few statistics to justify the cost of adding a second ATM machine. Using a Queue, simulate a waiting line at the ATM machine for a period of one hour. Make the following assumptions:

• With equal probability, a customer spends;
  • one minute, two minutes, or three minutes at the ATM machine
• During any minute:
  • No customer arrive (50% chance)
  • one customer arrives (40% chance)
  • two customers arrive (10% chance)

At the end of an hour; display the following summary statistics;

• the number of customers served, that is the number of people who accessed the ATM machine
• the average time that a customer waits in the line before being served, and
• the number of customers that remain in the waiting line at the end of the simulation

Assume that the ATM is available when the simulation begins and that no customers are waiting.

Design a class that models an ATM customer

• A customer knows arrival time and how much time he/she spend making an ATM transaction
  • Customer class should have the following methods
    • setArrivalTime()
    • setServiceTime()

The algorithm that simulates an ATM waiting line uses a loop that ticks through a 60min simulation

• Determine the number of new customers 0,1,2, for each customer
  • place the customer in a queue
• If there are customers waiting and the ATM is available
  • remove a customer from the queue
  • increment the number of customers served
  • add to the total waiting time of the customer
  • update the time the ATM is next available
• Print the summary statistics

Answer 1

Solution:

...............................................................................................................................................................

// Customer.java

public class Customer {

      // attributes

      private int arrivalTime;

      private int serviceTime;

      private int finishTime;

      // constructor to initialize all fields to 0

      public Customer() {

            arrivalTime = 0;

            serviceTime = 0;

            finishTime = 0;

      }

      // constructor taking arrival and service times

      public Customer(int arrivalTime, int serviceTime) {

            this.arrivalTime = arrivalTime;

            this.serviceTime = serviceTime;

      }

      // getters and setters

      public int getArrivalTime() {

            return arrivalTime;

      }

      public void setArrivalTime(int arrivalTime) {

            this.arrivalTime = arrivalTime;

      }

      public int getServiceTime() {

            return serviceTime;

      }

      public void setServiceTime(int serviceTime) {

            this.serviceTime = serviceTime;

      }

      public void setFinishTime(int finishTime) {

            this.finishTime = finishTime;

      }

      public int getFinishTime() {

            return finishTime;

      }

}

// ATMSimulation.java

import java.util.LinkedList;

import java.util.Queue;

import java.util.Random;

public class ATMSimulation {

      public static void main(String[] args) {

            // creating a Random object for random number generation

            Random random = new Random();

            // creating a Queue of Customer objects

            Queue<Customer> customerQueue = new LinkedList<Customer>();

            // initializing required variables

            // a variable to denote if the ATM is currently free, if this is 0, it

            // means that the ATM is free, else it will take currentAtmStatus

            // minutes to be free

            int currentAtmStatus = 0;

            // number of customers served

            int numCustomersServed = 0;

            // total waiting time

            int totalWaitingTime = 0;

            // looping for 60 times

            for (int i = 0; i < 60; i++) {

                  int newCustomers = 0;

                  // generating a number between 0 and 99

                  int probability = random.nextInt(100);

                  // if the number is less than 10, 2 new customers are added

                  if (probability < 10) {

                       newCustomers = 2;

                  } else if (probability >= 10 && probability < 50) {

                       // number is greater than 10 and less than 50, 1 new customer

                       // is added

                       newCustomers = 1;

                  } else {

                       // in all other cases (50%), no customers are added

                       newCustomers = 0;

                  }

                  // looping and adding newCustomers number of customers

                  for (int j = 0; j < newCustomers; j++) {

                       // creating a customer with i arrival time and a random service

                       // time between 1 and 3

                       Customer c = new Customer(i, random.nextInt(3) + 1);

                       // adding to queue

                       customerQueue.add(c);

                  }

                  // now checking if queue is empty and ATM is free

                  if (!customerQueue.isEmpty() && currentAtmStatus == 0) {

                       // removing oldest customer in the queue

                       Customer c = customerQueue.remove();

                       // adding his service time to currentAtmStatus, so that the ATM

                       // will be free only after currentAtmStatus minutes from now

                       currentAtmStatus += c.getServiceTime();

                       // setting finish time

                       c.setFinishTime(i + c.getServiceTime());

                       // finding waiting time, and adding to total waiting time

                       totalWaitingTime += c.getFinishTime() - c.getArrivalTime()

                                   - c.getServiceTime();

                       // incrementing number of customers served

                       numCustomersServed++;

                  }

                  // every minute passes, currentAtmStatus is decremented (if it is

                  // above 0)

                  if (currentAtmStatus > 0) {

                       currentAtmStatus--;

                  }

            }

            //finally displaying all stats

            System.out.println("Number of customers served: " + numCustomersServed);

            //finding average waiting time

            double avgWaitingTime = (double) totalWaitingTime / numCustomersServed;

            System.out.printf("Average waiting time (minutes): %.2f\n",

                       avgWaitingTime);

            System.out.println("Number of customers still in queue "

                       + "at the end of simulation: " + customerQueue.size());

      }

}

/*OUTPUT1*/

Number of customers served: 33

Average waiting time (minutes): 8.33

Number of customers still in queue at the end of simulation: 10

/*OUTPUT2*/

Number of customers served: 27

Average waiting time (minutes): 13.26

Number of customers still in queue at the end of simulation: 7

/*OUTPUT3*/

Number of customers served: 29

Average waiting time (minutes): 4.76

Number of customers still in queue at the end of simulation: 4