Answer: Java Implementation — Fuel_Monitor Class and Test Program

1. Class Design & Requirements Breakdown

Encapsulation Strategy:

• Private Instance Variables: All state variables are declared private to enforce encapsulation and prevent direct unauthorized alteration.
  • tank_capacity: Total capacity of the fuel tank (in Litres).
  • efficiency: Fuel efficiency / mileage (in Kilometers per Litre).
  • fuel_in_tank: Current amount of fuel available in the tank (initialized to 0.0).

Public Methods:

1. Fuel_Monitor(double capacity, double efficiency): Parameterized constructor to initialize the vehicle specifications.
2. getStatus(): Returns a formatted summary of initial tank size, efficiency, and current fuel.
3. add_fuel(double amount): Safely adds fuel up to maximum capacity and calculates how much fuel was actually filled.
4. drive_distance(double distance): Simulates driving a specified distance, calculates fuel consumed ($\text{fuel\_used} = \frac{\text{distance}}{\text{efficiency}}$), updates the remaining fuel in tank, and returns the actual distance travelled.
5. max_drive_distance(): Returns the total distance the vehicle can travel with the current remaining fuel in tank ($\text{fuel\_in\_tank} \times \text{efficiency}$).

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2. Complete Java Code

import java.util.Scanner;

class Fuel_Monitor {
    // Private instance variables for encapsulation
    private double tank_capacity;  // Maximum fuel tank size (Litres)
    private double efficiency;     // Mileage (km per Litre)
    private double fuel_in_tank;   // Current fuel in tank (Litres)

    // Constructor to initialize tank capacity and vehicle efficiency
    public Fuel_Monitor(double tank_capacity, double efficiency) {
        this.tank_capacity = tank_capacity;
        this.efficiency = efficiency;
        this.fuel_in_tank = 0.0; // Initialized to zero as specified
    }

    // Method to return initial specifications and current fuel status
    public String getStatus() {
        return "Initial Tank Size: " + tank_capacity + " L | " +
               "Initial Efficiency: " + efficiency + " km/L | " +
               "Current Fuel: " + fuel_in_tank + " L";
    }

    // Accessor methods
    public double get_ini_tank_size() { return tank_capacity; }
    public double get_ini_effi() { return efficiency; }
    public double get_fuel_in_tank() { return fuel_in_tank; }

    // Method to add fuel to the tank
    public double add_fuel(double amount) {
        if (amount <= 0) {
            System.out.println("Invalid fuel amount. Please enter a positive value.");
            return 0.0;
        }

        double available_space = tank_capacity - fuel_in_tank;

        if (amount <= available_space) {
            fuel_in_tank += amount;
            System.out.println("Added " + amount + " L. Current fuel in tank: " + fuel_in_tank + " L");
            return amount;
        } else {
            // Fill tank to maximum capacity
            fuel_in_tank = tank_capacity;
            System.out.println("Tank Full! Only " + available_space + " L could be filled. (Overflow: " + (amount - available_space) + " L discarded)");
            return available_space;
        }
    }

    // Method to drive a given distance and compute leftover fuel
    public double drive_distance(double distance) {
        if (distance <= 0) {
            System.out.println("Distance must be greater than zero.");
            return 0.0;
        }

        // Maximum distance possible with current fuel
        double max_possible_distance = fuel_in_tank * efficiency;

        if (distance <= max_possible_distance) {
            double fuel_consumed = distance / efficiency;
            fuel_in_tank -= fuel_consumed;
            System.out.println("Travelled " + distance + " km. Fuel consumed: " + String.format("%.2f", fuel_consumed) + " L.");
            System.out.println("Fuel left in tank: " + String.format("%.2f", fuel_in_tank) + " L.");
            return distance;
        } else {
            System.out.println("Not enough fuel to travel " + distance + " km!");
            System.out.println("Vehicle travelled maximum possible: " + String.format("%.2f", max_possible_distance) + " km before running out of fuel.");
            fuel_in_tank = 0.0;
            return max_possible_distance;
        }
    }

    // Method returning max distance possible with current fuel
    public double get_max_possible_distance() {
        return fuel_in_tank * efficiency;
    }
}

// Test Program
public class TestFuelMonitor {
    public static void main(String[] args) {
        System.out.println("=== VEHICLE FUEL MONITOR SIMULATION ===
");

        // Create a vehicle with 50 Litre tank capacity and 15 km/L efficiency
        Fuel_Monitor car = new Fuel_Monitor(50.0, 15.0);

        // 1. Check initial status
        System.out.println("1. Initial Status:");
        System.out.println(car.getStatus());
        System.out.println();

        // 2. Add Fuel
        System.out.println("2. Adding 30 Litres of Fuel:");
        car.add_fuel(30.0);
        System.out.println("Max drivable range now: " + car.get_max_possible_distance() + " km
");

        // 3. Drive 150 km
        System.out.println("3. Driving 150 km:");
        car.drive_distance(150.0);
        System.out.println();

        // 4. Drive another 200 km
        System.out.println("4. Driving 200 km:");
        car.drive_distance(200.0);
        System.out.println();

        // 5. Try to drive more distance than fuel permits
        System.out.println("5. Attempting to drive 200 km with remaining fuel:");
        car.drive_distance(200.0);
        System.out.println();

        // 6. Overfill test
        System.out.println("6. Refueling with 60 Litres (Exceeds capacity):");
        car.add_fuel(60.0);
        System.out.println(car.getStatus());
    }
}

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3. Sample Program Output

=== VEHICLE FUEL MONITOR SIMULATION ===

1. Initial Status:
Initial Tank Size: 50.0 L | Initial Efficiency: 15.0 km/L | Current Fuel: 0.0 L

2. Adding 30 Litres of Fuel:
Added 30.0 L. Current fuel in tank: 30.0 L
Max drivable range now: 450.0 km

3. Driving 150 km:
Travelled 150.0 km. Fuel consumed: 10.00 L.
Fuel left in tank: 20.00 L.

4. Driving 200 km:
Travelled 200.0 km. Fuel consumed: 13.33 L.
Fuel left in tank: 6.67 L.

5. Attempting to drive 200 km with remaining fuel:
Not enough fuel to travel 200.0 km!
Vehicle travelled maximum possible: 100.00 km before running out of fuel.

6. Refueling with 60 Litres (Exceeds capacity):
Tank Full! Only 50.0 L could be filled. (Overflow: 10.0 L discarded)
Initial Tank Size: 50.0 L | Initial Efficiency: 15.0 km/L | Current Fuel: 50.0 L