Object-Oriented Design• Patterns: Singleton, Factory Method

Parking Lot System

Medium

Problem Summary

Design a multi-level parking lot that can accommodate different vehicle types, handle ticketing, and process billing dynamically.

Functional Scope

Support multiple floors and spot types (Compact, Large, Motorcycle).
Process vehicle check-in (issue ticket, assign spot) and check-out (compute fee, release spot).
Thread-safe singleton control for the main ParkingLot instance.
Support dynamic fare calculation based on hour counts and vehicle types.

Entity-Relationship (ER) Schema

ParkingLot [1] <---> [*] ParkingFloor
ParkingFloor [1] <---> [*] ParkingSpot
ParkingTicket [1] <---> [1] ParkingSpot
ParkingTicket [1] <---> [1] Vehicle

Design Approach

Define a clean class hierarchy for Vehicles and ParkingSpots. Ensure concurrency control on spot allocation (synchronized methods) so multiple gates don't double-book the same physical spot.

Core Classes & Models

ParkingLot (Singleton)ParkingFloor (List of Spots)ParkingSpot (Base class for CompactSpot, LargeSpot, etc.)Vehicle (Base class for Car, Motorcycle, Truck)ParkingTicket (Tracks entry/exit times and spot references)

Code Blueprint

public class ParkingLot {
    private static ParkingLot instance;
    private ParkingLot() {}
    public static synchronized ParkingLot getInstance() {
        if (instance == null) instance = new ParkingLot();
        return instance;
    }
}