Parking Lot System Design | Object-Oriented Design Interview Question

Requirements

• 10K to 30K parking slots.
• Assume there are 4 entrances and 4 exits.
• Ticket and spot allocated at the entrance.
• The spot should be near the entrance the user entered.
• Different types of spots for bike, handicap, cars, truck.
• Hourly parking rate.
• Pay parking fee using cash and cards.
• Monitoring system for total cars entered etc.

Different actors

• Parking lot system
• Entry/exit terminal
• Printer
• Payment processor
• Parking spot
• Ticket
• Database
• Monitoring system

 Parking spot

1. Parent class parking spot
2. Child class handicapped parking spot
3. Child class car parking spot
4. Child class truck parking spot

 Ticket

1. Ticket class
2. Ticket id
3. Parking spot id
4. Parking spot type
5. Issue time

 Terminal

1. Parent class terminal
2. Child class entry terminal: getTicket(parkingSpotType)
3. Child class exit terminal: acceptTicket(ticket)

 Parking assignment strategy

1. Class Parking assignment strategy
2. Get parking spot method
3. Release parking spot method
4. Since we have 4 entrances we will have 4 heaps.
5. Once a parking spot is reserved make sure you to remove it from all the 4 heaps.

Payment

1. Parent class Payment processor
2. Child class credit card payment processor
3. Child class cash payment processor

Tariff calculator

• Calculate tariff method(start time,  parking spot type)

Monitoring system

• Use logger

Parking lot application

• This application uses a singleton design system.
• Will be composed of above smaller objects.
• Use a factory design pattern to instantiate above smaller objects.
• Application accept XML configuration as input. Input like parking spot type,  payment type.