Design a Logistics System

Design a Logistics System (Object Oriented Design). Tell about the different classes and their relationships with each-other. It is not a System Design question, so scope of this question is only to define different classes (with it’s attributes and methods)

Asked In: Adobe , Paytm

Solution: Let’s assume we want to design a Logistics System with following basic functionality:

1.  The system can take an order to deliver it to a given destination. 
2.  The order will be a list of items and there is a cost of each order to process. 
3. User has to register himself / herself to use this system. 
4. User can track his / her order. 
5. Orders will be shipped by bike or truck, but only a single order will be shipped by a single vehicle.
6. These type of questions are asked in interviews to Judge the Object Oriented Design skill of a candidate. So, first of all we should think about the classes.
7. The main classes will be:

• User 
• Item 
• Vehicle 
• Location 
• payment details 
• Order 
• LogisticsSystem

The User class is for users/clients/customers, who will be charged to get their items delivered.

Java

public class User {

    private int userId;
    private String name;
    private Location address;
    private String mobNo;
    private String emailId;

    public int getUserId() { return userId; }

    public void setUserId(int userId)
    {
        this.userId = userId;
    }

    public String getName() { return name; }

    public void setName(String name) { this.name = name; }

    public Location getAddress() { return address; }

    public void setAddress(Location address)
    {
        this.address = address;
    }

    public String getMobNo() { return mobNo; }

    public void setMobNo(String mobNo)
    {
        this.mobNo = mobNo;
    }

    public String getEmailId() { return emailId; }

    public void setEmailId(String emailId)
    {
        this.emailId = emailId;
    }
}

Item class represents an item that will be shipped. An order will contain a list of items.

Java

public class Item {

    private String name;
    private int price;
    private int volume;
    private int weight;

    public String getName() { return name; }

    public void setName(String name) { this.name = name; }

    public int getPrice() { return price; }

    public void setPrice(int price) { this.price = price; }

    public int getVolume() { return volume; }

    public void setVolume(int volume)
    {
        this.volume = volume;
    }

    public int getWeight() { return weight; }

    public void setWeight(int weight)
    {
        this.weight = weight;
    }
}

Location class simply represents the address. 

Java

public class Location {

    private Double longitude;
    private Double latitude;

    public Double getLongitude() { return longitude; }

    public void setLongitude(Double longitude)
    {
        this.longitude = longitude;
    }

    public Double getLatitude() { return latitude; }

    public void setLatitude(Double latitude)
    {
        this.latitude = latitude;
    }
}

The Vehicle class represents the vehicle that will be used to ship/deliver an order. 

It will be of two types:

1. Bike 
2. Truck

Java

public class Vehicle {

    private int id;
    private String vehicleNo;
    private int capacity;
    private Location currentPosition;
    private VehicleStatus currentStatus;

    public Vehicle(int id, String vehicleNo, int capacity)
    {
        this.id = id;
        this.vehicleNo = vehicleNo;
        this.capacity = capacity;
    }

    public int getId() { return id; }

    public void setId(int id) { this.id = id; }

    public String getVehicleNo() { return vehicleNo; }

    public void setVehicleNo(String vehicleNo)
    {
        this.vehicleNo = vehicleNo;
    }

    public int getCapacity() { return capacity; }

    public void setCapacity(int capacity)
    {
        this.capacity = capacity;
    }

    public Location getCurrentPosition()
    {
        return currentPosition;
    }

    public void setCurrentPosition(Location currentPosition)
    {
        this.currentPosition = currentPosition;
    }

    public VehicleStatus getCurrentStatus()
    {
        return currentStatus;
    }

    public void
    setCurrentStatus(VehicleStatus currentStatus)
    {
        this.currentStatus = currentStatus;
    }
}

The bike has only 10 unit of capacity.

Java

public class Bike extends Vehicle {

    private final static int capacityofBike = 10;

    public Bike(int id, String vehicleNo)
    {

        super(id, vehicleNo, capacityofBike);
    }
}

The truck has only 100 unit of capacity (10 times more than bike).

Java

public class Truck extends Vehicle {

    private final static int capacityofTruck = 100;

    public Truck(int id, String vehicleNo)
    {
        super(id, vehicleNo, capacityofTruck);
    }
}

Enum for current status of a vehicle:

Java

public enum VehicleStatus {
    FREE,
    BUSY,
    NOT_WORKING;
}

Enum for OrderPriority:

Java

public enum OrderPriority {
    LOW,
    MEDIUM,
    HIGH;
}

Enum for OrderStatus:

Java

public enum OrderStatus {
    DELIVERED,
    PROCESSING,
    CANCELLED;
}

Enum for PaymentMode:

Java

public enum PaymentMode {

    NET_BANKING,
    CREDIT_CARD,
    DEBIT_CARD;
}

Enum for PaymentStatus:

Java

public enum PaymentStatus {
    PAID,
    UNPAID;
}

The PaymentDetails class contains the information of payment related things so that in any case the order is cancelled, it can be refunded easily.

Java

public class PaymentDetails {
    private PaymentMode paymentMode;
    private String transactionId;
    private int amount;
    private PaymentStatus paymentStatus;
    private String cardNumber;

    public PaymentMode getPaymentMode()
    {
        return paymentMode;
    }

    public void setPaymentMode(PaymentMode paymentMode)
    {
        this.paymentMode = paymentMode;
    }

    public String getTransactionId()
    {
        return transactionId;
    }

    public void setTransactionId(String transactionId)
    {
        this.transactionId = transactionId;
    }

    public int getAmount() { return amount; }

    public void setAmount(int amount)
    {
        this.amount = amount;
    }

    public PaymentStatus getPaymentStatus()
    {
        return paymentStatus;
    }

    public void
    setPaymentStatus(PaymentStatus paymentStatus)
    {
        this.paymentStatus = paymentStatus;
    }

    public String getCardNumber() { return cardNumber; }

    public void setCardNumber(String cardNumber)
    {
        this.cardNumber = cardNumber;
    }
}

The Order class contains all the information of an order. All fields are self-explanatory.

Java

import java.util.Date;
import java.util.List;

public class Order {

    private int orderId;
    private OrderPriority priority_of_order;
    private User sender;
    private Location destination;
    private PaymentDetails paymentDetails;
    private List<Item> items;
    private Long totalWeight;
    private OrderStatus currentStatus;
    private Date timeOfOrderPlaced;
    private Date timeOfOrderDelivery;
    private Vehicle vehicleOfThisOrder;

    public int getOrderId() { return orderId; }

    public void setOrderId(int orderId)
    {
        this.orderId = orderId;
    }

    public OrderPriority getPriority_of_order()
    {
        return priority_of_order;
    }

    public void
    setPriority_of_order(OrderPriority priority_of_order)
    {
        this.priority_of_order = priority_of_order;
    }

    public User getSender() { return sender; }

    public void setSender(User sender)
    {
        this.sender = sender;
    }

    public Location getDestination() { return destination; }

    public void setDestination(Location destination)
    {
        this.destination = destination;
    }

    public PaymentDetails getPaymentDetails()
    {
        return paymentDetails;
    }

    public void
    setPaymentDetails(PaymentDetails paymentDetails)
    {
        this.paymentDetails = paymentDetails;
    }

    public List<Item> getItems() { return items; }

    public void setItems(List<Item> items)
    {
        this.items = items;
    }

    public Long getTotalWeight() { return totalWeight; }

    public void setTotalWeight(Long totalWeight)
    {
        this.totalWeight = totalWeight;
    }

    public OrderStatus getCurrentStatus()
    {
        return currentStatus;
    }

    public void setCurrentStatus(OrderStatus currentStatus)
    {
        this.currentStatus = currentStatus;
    }

    public Date getTimeOfOrderPlaced()
    {
        return timeOfOrderPlaced;
    }

    public void setTimeOfOrderPlaced(Date timeOfOrderPlaced)
    {
        this.timeOfOrderPlaced = timeOfOrderPlaced;
    }

    public Date getTimeOfOrderDelivery()
    {
        return timeOfOrderDelivery;
    }

    public void
    setTimeOfOrderDelivery(Date timeOfOrderDelivery)
    {
        this.timeOfOrderDelivery = timeOfOrderDelivery;
    }

    public Vehicle getVehicleOfThisOrder()
    {
        return vehicleOfThisOrder;
    }

    public void
    setVehicleOfThisOrder(Vehicle vehicleOfThisOrder)
    {
        this.vehicleOfThisOrder = vehicleOfThisOrder;
    }
}

The main class (LogisticsSystem) which stores all the information of users, orders and vehicles. It has the methods like takeAnOrder(), processOrder() etc.

Java

import java.util.ArrayList;
import java.util.List;

public class LogisticsSystem {

    private List<Order> orders;
    private List<Vehicle> vehicles;
    private List<User> users;

    public LogisticsSystem()
    {
        this.orders = new ArrayList<Order>();
        this.vehicles = new ArrayList<Vehicle>();
        this.users = new ArrayList<User>();
    }

    public void takeAnOrder(Order order)
    {
        System.out.println("Adding an order to the system");
        orders.add(order);
    }

    public void processOrder(Order order)
    {
        System.out.println(
            "Processing an order of the system");
    }

    public Location trackOrder(int orderId)
    {
        System.out.println(
            "Tracking an order of the system");
        Location location = null;
        // location = findLocationOfGivenOrder();
        return location;
    }

    public void cacelOrder(Order order)
    {
        System.out.println(
            "Going to cancel an order of the system");
    }

    public void registerNewUser(User user)
    {
        System.out.println(
            "Registering a new user to the system");
        users.add(user);
    }

    public List<Order> getOrders() { return orders; }

    public void setOrders(List<Order> orders)
    {
        this.orders = orders;
    }

    public List<Vehicle> getVehicles() { return vehicles; }

    public void setVehicles(List<Vehicle> vehicles)
    {
        this.vehicles = vehicles;
    }

    public List<User> getUsers() { return users; }

    public void setUsers(List<User> users)
    {
        this.users = users;
    }
}

This is the test class to test the application.

Java

package com.shashi.oodesign;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class Apptest {

    public static void main(String[] args)
    {

        User user = new User();
        user.setUserId(1);
        user.setName("Shashi");
        user.setEmailId("shashi@gmail.com");

        Item item1 = new Item();
        item1.setName("item1");
        item1.setPrice(20);

        Item item2 = new Item();
        item2.setName("item2");
        item2.setPrice(40);

        List<Item> items = new ArrayList<Item>();
        items.add(item1);
        items.add(item2);

        PaymentDetails paymentDetails
            = new PaymentDetails();
        paymentDetails.setAmount(100);
        paymentDetails.setPaymentMode(
            PaymentMode.CREDIT_CARD);
        paymentDetails.setCardNumber("12345678");

        Location destination = new Location();
        destination.setLatitude(73.23);
        destination.setLongitude(132.34);

        Order order = new Order();
        order.setOrderId(1);
        order.setItems(items);
        order.setCurrentStatus(OrderStatus.PROCESSING);
        order.setDestination(destination);
        order.setPaymentDetails(paymentDetails);
        order.setTimeOfOrderDelivery(new Date());

        LogisticsSystem logisticsSystem
            = new LogisticsSystem();
        logisticsSystem.registerNewUser(user);
        logisticsSystem.takeAnOrder(order);
        logisticsSystem.processOrder(order);
    }
}