Parking Lot System Design: Objects and Relationships

Designing a parking lot system is a common exercise in object-oriented design interviews. This system can be complex, involving various entities and their relationships. In this article, we will explore the key objects involved in a parking lot system and how they interact with each other.

Key Objects in the Parking Lot System

  1. ParkingLot
    The main entity that represents the parking lot. It contains information about the total number of spaces, available spaces, and the vehicles parked.

  2. ParkingSpace
    Represents an individual parking space within the parking lot. Each parking space can be either occupied or available. It may also have attributes like size (compact, standard, oversized).

  3. Vehicle
    Represents a vehicle that can park in the parking lot. This can be further divided into subclasses such as Car, Motorcycle, and Truck, each with specific attributes.

  4. Ticket
    Represents a parking ticket issued to a vehicle when it enters the parking lot. It contains information such as the entry time, vehicle details, and a unique identifier.

  5. ParkingAttendant
    Represents the personnel managing the parking lot. They can issue tickets, manage parking spaces, and assist customers.

Relationships Between Objects

Understanding the relationships between these objects is crucial for effective system design:

  • ParkingLot to ParkingSpace: A parking lot contains multiple parking spaces. This is a one-to-many relationship, where one parking lot can have many parking spaces.
  • ParkingSpace to Vehicle: A parking space can be occupied by one vehicle at a time, establishing a one-to-one relationship. However, a vehicle can occupy different spaces over time.
  • Ticket to Vehicle: Each ticket is associated with one vehicle, creating a one-to-one relationship. A vehicle can have multiple tickets over time, but each ticket corresponds to a single vehicle.
  • ParkingAttendant to ParkingLot: A parking attendant manages one or more parking lots, which is a one-to-many relationship.

Example Class Diagram

To visualize the relationships, consider the following simplified class diagram:

+----------------+       +----------------+       +----------------+
|   ParkingLot   | 1   *|  ParkingSpace  | 1   1|     Vehicle     |
+----------------+-------+----------------+-------+----------------+
| - totalSpaces  |       | - isOccupied   |       | - licensePlate  |
| - availableSpaces|     | - size         |       | - type          |
| + parkVehicle() |       | + assignVehicle()|     | + getDetails()  |
| + removeVehicle()|       | + freeSpace()  |       +----------------+
+----------------+       +----------------+       +----------------+

+----------------+       +----------------+
|     Ticket     | 1   1| ParkingAttendant|
+----------------+-------+----------------+
| - ticketId     |       | - name         |
| - entryTime    |       | + issueTicket()|
| + getDetails() |       +----------------+
+----------------+

Conclusion

Designing a parking lot system involves identifying the key objects and their relationships. By understanding these components, software engineers can create a robust and scalable system. This exercise not only tests your design skills but also your ability to think critically about real-world systems.

In preparation for technical interviews, practice designing similar systems, focusing on object-oriented principles and relationships. This will enhance your problem-solving skills and prepare you for complex design challenges.