- Vehicle
- size of vehicle (small, medium, large)
- status of vehicle (run or parked)
- findSlot()
- park()
- leave()
- Car, Bike, Bus, Truck... extends Vehicle
- Slot
- size of slot
- status (available or not)
- occupy()
- release()
- ParkingLot
- hold slots in parking lot
- totalSlots()
- occupiedSlots()
- availableSlots()
