Code for the Parking Lot

Let's write the code for the classes that we have designed, in different languages in this lesson.

We'll cover the following

Parking lot classes
Wrapping up

We’ve gone over the different aspects of the parking lot system and observed the attributes attached to the problem using various UML diagrams. Let’s explore the more practical side of things, where we will work on implementing the parking lot system using multiple languages. This is usually the last step in an object-oriented design interview process.

We have chosen the following languages to write the skeleton code of the different classes present in the parking lot system:

Java
C#
Python
C++
JavaScript

Parking lot classes#

In this section, we will provide the skeleton code of the classes designed in the class diagram lesson.

Note: For simplicity, we aren’t defining getter and setter functions. The reader can assume that all class attributes are private and accessed through their respective public getter methods and modified only through their public method functions.

Enumerations and custom data type#

First of all, we will define all the enumerations required in the parking lot. According to the class diagram, there are two enumerations used in the system i.e., PaymentStatus and AccountStatus. The code to implement these enumerations and custom data types is as follows:

Note: JavaScript does not support enumerations, so we will be using the Object.freeze() method as an alternative that freezes an object and prevents further modifications.

// Enumeration
enum PaymentStatus {
  COMPLETED, 
  FAILED, 
  PENDING, 
  UNPAID, 
  REFUNDED
}
enum AccountStatus {
  ACTIVE, 
  CLOSED, 
  CANCELED, 
  BLACKLISTED, 
  NONE
}
// Custom Person data type class
public class Person {
  private String name;
  private String address;
  private String phone;
  private String email;
}
// Custom Address data type class
public class Address {
  private int zipCode;
  private String address;
  private String city;
  private String state;

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Definition for the constants

// ParkingSpot is an abstract class
public abstract class ParkingSpot {
  private int id;
  private boolean isFree;
  private Vehicle vehicle;
  public boolean getIsFree();
  public abstract boolean assignVehicle(Vehicle vehicle);
  public boolean removeVehicle(){
    // definition
  }
}
public class Handicapped extends ParkingSpot {
  public boolean assignVehicle(Vehicle vehicle) {
    // definition
  }
}
public class Compact extends ParkingSpot {
  public boolean assignVehicle(Vehicle vehicle) {
    // definition
  }
}
public class Large extends ParkingSpot {
  public boolean assignVehicle(Vehicle vehicle) {
    // definition
  }
}

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ParkingSpot and its derived classes

// Vehicle is an abstract class
public abstract class Vehicle {
  private int licenseNo;
  public abstract void assignTicket(ParkingTicket ticket);
}
public class Car extends Vehicle {
  public void assignTicket(ParkingTicket ticket) {
    // definition
  }
}
public class Van extends Vehicle {
  public void assignTicket(ParkingTicket ticket) {
    // definition
  }
}
public class Truck extends Vehicle {
  public void assignTicket(ParkingTicket ticket) {
    // definition
  }
}
public class MotorCycle extends Vehicle {
  public void assignTicket(ParkingTicket ticket) {
    // definition
  }
}

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Vehicle and its child classes

public abstract class Account {
  // Data members
  private String userName;
  private String password;
  private Person person; // Refers to an instance of the Person class
  private AccountStatus status; // Refers to the AccountStatus enum
  public abstract boolean resetPassword();
}
public class Admin extends Account {
  // spot here refers to an instance of the ParkingSpot class
  public boolean addParkingSpot(ParkingSpot spot);
  // displayBoard here refers to an instance of the DisplayBoard class
  public boolean addDisplayBoard(DisplayBoard displayBoard);
  // entrance here refers to an instance of the Entrance class
  public boolean addEntrance(Entrance entrance);
  // exit here refers to an instance of the Exit class
  public boolean addExit(Exit exit);
  // Will implement the functionality in this class
  public boolean resetPassword() {
    // definition
  }
}
public class ParkingAttendant extends Account {
  public boolean processTicket(String ticketNumber);
  // Will implement the functionality in this class
  public boolean resetPassword() {

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Account and its child classes

public class DisplayBoard {
  // Data members
  private int id;
  private Map<String, List<ParkingSpot>> parkingSpots;
  // Constructor
  public DisplayBoard(int id) {
    this.id = id;
    this.parkingSpots = new HashMap<>();
  }
  
  // Member function
  public void addParkingSpot(String spotType, List<ParkingSpot> spots);
  public void showFreeSlot();
}
public class ParkingRate {
  // Data members
  private double hours;
  private double rate;
  // Member function
  public void calculate();
}

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The DisplayBoard and ParkingRate classes

public class Entrance {
  // Data members 
  private int id;
  // Member function
  public ParkingTicket getTicket();
}
public class Exit {
  // Data members 
  private int id;
  // Member function
  public void validateTicket(ParkingTicket ticket){
    // Perform validation logic for the parking ticket
    // Calculate parking charges, if necessary
    // Handle the exit process
  }
}

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The Entrance and Exit classes

public class ParkingTicket {
    private int ticketNo;
    private Date timestamp;
    private Date exit;
    private double amount;
    private boolean status;
    // Following are the instances of their respective classes
    private Vehicle vehicle;
    private Payment payment;
    private Entrance entrance;
    private Exit exitIns;    
}

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The ParkingTicket class

// Payment is an abstract class
public abstract class Payment {
    private double amount;
    private PaymentStatus status;
    private Date timestamp;
    public abstract boolean initiateTransaction();
}
public class Cash extends Payment {
    public boolean initiateTransaction() {
        // definition
    }
}
public class CreditCard extends Payment {
    public boolean initiateTransaction() {
        // definition
    }
}

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Payment and its derived classes

public class ParkingLot {
    private int id;
    private String name;
    private String address;
    private ParkingRate parkingRate;
    private HashMap<String, Entrance> entrance;
    private HashMap<String, Exit> exit;
    // Create a hashmap that identifies all currently generated tickets using their ticket number
    private HashMap<String, ParkingTicket> tickets;
    // The ParkingLot is a singleton class that ensures it will have only one active instance at a time
    // Both the Entrance and Exit classes use this class to create and close parking tickets
    private static ParkingLot parkingLot = null;
    // Created a private constructor to add a restriction (due to Singleton)
    private ParkingLot() {
        // Call the name, address and parking_rate 
        // Create initial entrance and exit hashmaps respectively
    }
    // Created a static method to access the singleton instance of ParkingLot
    public static ParkingLot getInstance() {
        if (parkingLot == null) {
            parkingLot = new ParkingLot();
        }
        return parkingLot;
    }
    public boolean addEntrance(Entrance entrance){}

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The ParkingLot class

Activity Diagram for the Parking Lot

Getting Ready: Elevator System