Checkout.java

/*
The Checkout class simulates three different models for self-checkout stations at a 
grocery store to compare their efficiency:
1. One line for customers and n checkout stations
2. n lines for customers (customers choose the shortest line) 
3. n lines for customers (customers choose a random line)
The simulation is meant to run for 2 hours and reports statistics including the number of 
customers served, maximum queue length, and average waiting time.
*/

import java.util.*;

public class Checkout {
    // Model 1: One line, n stations
    public static void oneLine(int stations) {
        Queue<Customer> line = new Queue<>();
        int[] stationBusyTime = new int[stations];
        int totalCustomers = 0;
        int totalWaitTime = 0;
        int maxQueueLength = 0;
        Random rand = new Random();
        
        for (int time = 0; time < 7200; time++) {
            // Every 30 seconds, a new customer arrives
            if (time % 30 == 0) {
                int items = 5 + rand.nextInt(16);
                Customer newCustomer = new Customer(items, time);
                line.enqueue(newCustomer);
                if (line.size() > maxQueueLength) maxQueueLength = line.size();
            }
            // For each station, check if it's available
            for (int i = 0; i < stations; i++) {
                if (stationBusyTime[i] > 0) {
                    stationBusyTime[i]--;
                } else {
                    if (!line.isEmpty()) {
                        Customer current = line.dequeue();
                        // Calculate checkout time
                        int checkoutTime = current.getItems() * 2 + 15;
                        current.setStartTime(time);
                        current.setEndTime(time + checkoutTime);
                        totalCustomers++;
                        totalWaitTime += current.getStartTime() - current.getArrivalTime();
                        stationBusyTime[i] = checkoutTime;
                    }
                }
            }
        }
        System.out.println("Model 1: One Line, " + stations + " Stations ");
        System.out.println("Total Customers Served: " + totalCustomers);
        System.out.println("Average Wait Time (seconds): " + (totalCustomers == 0 ? 0 : totalWaitTime / totalCustomers));
        System.out.println("Maximum Queue Length Reached: " + maxQueueLength + "\n");
    }

    // Model 2: n lines, customer chooses shortest line
    public static void shortestLine(int stations) {
        Queue<Customer>[] lines = new Queue[stations];
        for (int i = 0; i < stations; i++) lines[i] = new Queue<>();
        int[] stationBusyTime = new int[stations];
        int totalCustomers = 0;
        int totalWaitTime = 0;
        int maxQueueLength = 0;

        Random rand = new Random();
        for (int time = 0; time < 7200; time++) {
            if (time % 30 == 0) {
                int items = 5 + rand.nextInt(16);
                Customer newCustomer = new Customer(items, time);
                int shortestLine = 0;
                for (int i = 1; i < stations; i++) {
                    if (lines[i].size() < lines[shortestLine].size()) shortestLine = i;
                }
                lines[shortestLine].enqueue(newCustomer);
                for (Queue<Customer> line : lines) {
                    if (line.size() > maxQueueLength) maxQueueLength = line.size();
                }
            }
            for (int i = 0; i < stations; i++) {
                if (stationBusyTime[i] > 0) {
                    stationBusyTime[i]--;
                } else {
                    if (!lines[i].isEmpty()) {
                        Customer current = lines[i].dequeue();
                        // Calculate checkout time
                        int checkoutTime = current.getItems() * 2 + 15;
                        current.setStartTime(time);
                        current.setEndTime(time + checkoutTime);
                        totalCustomers++;
                        totalWaitTime += current.getStartTime() - current.getArrivalTime();
                        stationBusyTime[i] = checkoutTime;
                    }
                }
            }
        }
        System.out.println("Model 2: Shortest Line, " + stations + " Stations");
        System.out.println("Total Customers Served: " + totalCustomers);
        System.out.println("Average Wait Time (seconds): " + (totalCustomers == 0 ? 0 : totalWaitTime / totalCustomers));
        System.out.println("Maximum Queue Length Reached: " + maxQueueLength + "\n");
    }

    // Model 3: n lines, customer chooses random line
    public static void randomLine(int stations) {
        Queue<Customer>[] lines = new Queue[stations];
        for (int i = 0; i < stations; i++) lines[i] = new Queue<>();
        int[] stationBusyTime = new int[stations];
        int totalCustomers = 0;
        int totalWaitTime = 0;
        int maxQueueLength = 0;
        Random rand = new Random();
        for (int time = 0; time < 7200; time++) {
            if (time % 30 == 0) {
                int items = 5 + rand.nextInt(16);
                Customer newCustomer = new Customer(items, time);
                int randomLine = rand.nextInt(stations);
                lines[randomLine].enqueue(newCustomer);
                for (Queue<Customer> line : lines) {
                    if (line.size() > maxQueueLength) maxQueueLength = line.size();
                }
            }
            for (int i = 0; i < stations; i++) {
                if (stationBusyTime[i] > 0) {
                    stationBusyTime[i]--; // Station is still working
                } else {
                    if (!lines[i].isEmpty()) {
                        Customer current = lines[i].dequeue();
                        // Calculate checkout time
                        int checkoutTime = current.getItems() * 2 + 15; // 2s/item + 15s to pay
                        current.setStartTime(time);
                        current.setEndTime(time + checkoutTime);

                        // Stats
                        totalCustomers++;
                        totalWaitTime += current.getStartTime() - current.getArrivalTime();

                        // Station is now busy
                        stationBusyTime[i] = checkoutTime;
                    }
                }
            }
        }

        // Print out results
        System.out.println("Model 3: Random Line, " + stations + " Stations");
        System.out.println("Total Customers Served: " + totalCustomers);
        System.out.println("Average Wait Time (seconds): " + (totalCustomers == 0 ? 0 : totalWaitTime / totalCustomers));
        System.out.println("Maximum Queue Length Reached: " + maxQueueLength + "\n");
    }

    public static void main(String[] args) {
        // Simulate 3 checkout stations with individual lines
        int stations = 3;
        oneLine(stations);
        shortestLine(stations);
        randomLine(stations);
    }
}