Car Rental System

Design a Car Rental System with vehicle management, state tracking, booking operations, pricing strategies, and loyalty programs.

What is the Car Rental System Problem?

Design a Car Rental System that manages a fleet of vehicles (cars, SUVs, trucks) with different states (Available, Rented, Maintenance, Retired). The system should support vehicle booking for specific date ranges, calculate rental costs based on vehicle type, duration, and location, check availability, handle pickup/dropoff at different locations, track vehicle damage, manage insurance options, and implement a loyalty program for customers.

In this problem, you’ll design a system that coordinates vehicle inventory, manages complex state transitions, implements flexible pricing strategies, and handles concurrent booking operations while maintaining data consistency.

Problem Overview

Design a comprehensive car rental system that manages vehicle inventory, handles bookings, calculates dynamic pricing, tracks vehicle conditions, and rewards loyal customers.

Core Requirements

Functional Requirements:

Vehicle Management: Manage fleet of vehicles including cars, SUVs, and trucks, each with unique identifiers, make, model, and year.
Vehicle States: Track vehicle states (Available, Rented, Maintenance, Retired) and handle state transitions based on operations.
Rental Booking: Allow customers to book vehicles for specific start and end dates with automatic state transitions.
Pricing: Calculate rental costs based on vehicle type, rental duration (daily/weekly/monthly), pickup/dropoff locations, and any applicable discounts.
Availability Check: Check vehicle availability for given dates considering existing bookings and vehicle states.
Pickup/Dropoff: Support pickup and dropoff at different locations with appropriate one-way fees.
Damage Tracking: Track vehicle condition and damage reports, automatically transitioning damaged vehicles to Maintenance state.
Insurance: Support multiple insurance options (Basic, Premium, Full Coverage) that can be added to bookings.
Loyalty Program: Track customer loyalty points based on rental costs and apply discounts based on loyalty status.

Non-Functional Requirements:

Object-Oriented Design: Clear separation of concerns with well-defined roles for each class.
Modularity: Easy to add new vehicle types, pricing strategies, or insurance options without modifying existing code.
Thread Safety: Booking operations, availability checks, and state transitions must be safe from race conditions.
State Management: Robust vehicle state management preventing invalid state transitions.
Reliability: Core rental logic should be robust, testable, and maintainable over time.

What’s Expected?

1. System Architecture

The system manages vehicles, bookings, customers, and locations through a centralized rental service.

2. Key Classes to Design

classDiagram
    class RentalService {
        -Map~String,Vehicle~ vehicles
        -Map~String,Booking~ bookings
        +searchAvailableVehicles()
        +bookVehicle()
        +returnVehicle()
    }
    
    class Vehicle {
        -VehicleState currentState
        -PricingStrategy pricingStrategy
        +rent()
        +returnVehicle()
        +startMaintenance()
    }
    
    class VehicleState {
        <<interface>>
        +rentVehicle()
        +returnVehicle()
    }
    
    class PricingStrategy {
        <<interface>>
        +calculatePrice()
    }

    RentalService --> Vehicle
    RentalService --> Booking
    Vehicle --> VehicleState
    Vehicle --> PricingStrategy
    Vehicle "1" -- "many" Booking

System Flow

Booking Flow (State Transitions)

Key Design Challenges

1. Managing Vehicle States

Vehicles transition between Available, Rented, Maintenance, and Retired states based on various operations. Invalid transitions must be prevented.

Solution: Use the State Pattern. Create state classes (AvailableState, RentedState, MaintenanceState, RetiredState) that encapsulate state-specific behavior. Each state defines which transitions are valid, preventing invalid operations.

2. Flexible Pricing Strategies

Pricing should vary based on vehicle type, rental duration (daily vs weekly vs monthly), and location (premium locations cost more).

Solution: Use the Strategy Pattern. Create pricing strategy classes (DailyPricingStrategy, WeeklyPricingStrategy, MonthlyPricingStrategy) that encapsulate different pricing algorithms. Vehicles can use different strategies, and strategies can be swapped at runtime.

3. Creating Different Vehicle Types

The system needs to create cars, SUVs, and trucks without exposing the creation logic or requiring changes to existing code when new types are added.

Solution: Use the Factory Pattern. Create a VehicleFactory interface with a VehicleFactoryImpl that creates instances based on vehicle type. This decouples creation logic and makes adding new vehicle types easy.

4. Concurrent Booking Operations

Multiple customers might try to book the same vehicle simultaneously, leading to double-booking.

Solution: Implement thread-safe operations using synchronized blocks/locks and concurrent collections. Availability checks and booking operations are atomic, preventing race conditions.

What You’ll Learn

By solving this problem, you’ll master:

✅ State Pattern - Managing complex lifecycles with clear state transitions.
✅ Strategy Pattern - Implementing flexible, swappable algorithms.
✅ Factory Pattern - Decoupling object creation from usage.
✅ Concurrency Control - Using locking mechanisms to prevent data corruption.
✅ System Design - Coordinating multiple entities (vehicles, bookings, customers) in a real-world scenario.

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