Main.java

import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;
import java.util.concurrent.atomic.AtomicInteger;

class ServiceStation {
    ArrayList<Car> waitingQueue;
    Semaphore mutex, empty, full, pumps;
    public final int totalCars;
    public AtomicInteger carsServicedCount;

    ServiceStation(int pumpsNumber, int queueSize, int totatlCars) {
        waitingQueue = new ArrayList<>(queueSize);
        mutex = new Semaphore(1);
        full = new Semaphore(0);
        empty = new Semaphore(queueSize);
        pumps = new Semaphore(pumpsNumber);
        this.totalCars = totatlCars;
        this.carsServicedCount = new AtomicInteger(0);
    }
}

class Pump implements Runnable {

    private int id;
    private ServiceStation station;
    private Random rand;

    public Pump(int id, ServiceStation station) {
        this.id = id;
        this.station = station;
        this.rand = new Random();
    }

    @Override
    public void run() {
        while (station.carsServicedCount.get() < station.totalCars) {
            Car c;
            try {
                station.full.P();
                station.mutex.P();
                c = station.waitingQueue.remove(0);
                station.carsServicedCount.incrementAndGet();
                station.mutex.V();
                station.empty.V();

                if (c == null) {
                    continue;
                }

                System.out.println("Pump " + id + ": " + c.getId() + " Occupied");
                station.pumps.P();
                System.out.println("Pump " + id + ": " + c.getId() + " login");
                System.out.println("Pump " + id + ": " + c.getId() + " begins service at Bay " + id);
                Thread.sleep(1000 + rand.nextInt(1000));
                System.out.println("Pump " + id + ": " + c.getId() + " finishes service");
                station.pumps.V();
                System.out.println("Pump " + id + ": Bay " + id + " is free");

            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }
}

class Semaphore {
    protected int count;

    protected Semaphore() {
        count = 0;
    }

    public Semaphore(int count) {
        if (count < 0) throw new IllegalArgumentException();
        this.count = count;
    }

    public synchronized void P() {
        count--;
        if (count < 0) {
            try {
                wait();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }

    public synchronized void V() {
        count++;
        if (count <= 0)
            notify();
    }

    public synchronized int getCount() {
        return count;
    }
}

class Car implements Runnable {
    private String id;
    private ServiceStation station;

    Car(String id, ServiceStation station) {
        this.id = id;
        this.station = station;

    }

    @Override
    public void run() {

        System.out.println(id + " arrived");

        station.empty.P();
        station.mutex.P();

        station.waitingQueue.add(this);
        System.out.println(id + " entered the queue (waiting area size = " + station.waitingQueue.size() + ")");

        station.mutex.V();
        station.full.V();
    }

    public String getId() {
        return id;
    }
}

public class Main {

    public static boolean isInteger(String s) {
        if (s == null || s.isEmpty()) return false;
        try {
            Integer.parseInt(s);
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }

    public static void main(String[] args) throws InterruptedException {

        String input;
        Scanner in = new Scanner(System.in);
        String[] msg = new String[]{"Waiting area capacity: ", "Number of service bays (pumps): ", "Cars arriving (order): "};
        int idx = 0, area = 0, NumPumps = 0, NumCars = 0;
        String[] names = {};

        // Taking input and validations are made
        while (idx < 3) {

            if (idx == 0) {
                System.out.println(msg[idx]);
                input = in.nextLine();
                if (isInteger(input) && Integer.parseInt(input) <= 10 && Integer.parseInt(input) >= 1) {
                    idx++;
                    area = Integer.parseInt(input);
                } else System.out.println("Invalid input!");
            } else if (idx == 1) {
                System.out.println(msg[idx]);
                input = in.nextLine();
                if (isInteger(input) && Integer.parseInt(input) >= 1) {
                    idx++;
                    NumPumps = Integer.parseInt(input);
                } else System.out.println("Invalid input!");
            } else {
                System.out.println(msg[idx]);
                input = in.nextLine();
                names = input.split(",");

                NumCars = names.length;
                idx++;
            }
        }
        ServiceStation station = new ServiceStation(NumPumps, area, NumCars);
        Thread[] Pumps = new Thread[NumPumps];
        Thread[] Cars = new Thread[NumCars];

        for (int i = 0; i < NumPumps; i++) {
            Pumps[i] = new Thread(new Pump(i + 1, station));
            Pumps[i].start();
        }

        for (int i = 0; i < NumCars; i++) {
            Cars[i] = new Thread(new Car(names[i], station));
            Cars[i].start();
            Thread.sleep(300);
        }
    }
}