Object-Oriented Modeling & UML Class Diagrams

Hints

• Think about what data each entity needs to store (attributes)
• Think about what actions each entity can perform (methods)
• Consider: Does a Rental "own" the Car and Customer, or just reference them?

Example Solution Structure (Mermaid)

classDiagram
    class Car {
        -String licensePlate
        -String brand
        -String model
        -String color
        -double dailyRate
        -boolean available
        +isAvailable() boolean
        +setAvailable(status) void
        +calculateRentalCost(days) double
    }

    class Customer {
        -String customerId
        -String name
        -String driverLicense
        -String phone
        -String email
        +getContactInfo() String
    }

    class Rental {
        -String rentalId
        -Date startDate
        -Date endDate
        -double totalCost
        +calculateDuration() int
        +calculateTotalCost() double
        +isActive() boolean
    }

    Customer "1" -- "0..*" Rental : makes
    Car "1" -- "0..*" Rental : subject of

Key Questions to Answer

• What's the relationship between Cart and CartItem?
• What's the relationship between Order and OrderItem?
• Should Address be its own class or part of Customer?
• How do you represent that OrderItem captures the price at purchase time (not current price)?

Partial Solution (Mermaid)

classDiagram
    class Product {
        -String sku
        -String name
        -String description
        -double price
        -int stockQuantity
        +isInStock() boolean
        +reduceStock(qty) void
    }

    class Category {
        -String categoryId
        -String name
        -String description
    }

    class Customer {
        -String customerId
        -String email
        -String passwordHash
        +placeOrder() Order
    }

    class Address {
        -String street
        -String city
        -String zipCode
        -String country
    }

    Product "*" --> "1" Category : belongs to
    Customer "1" *-- "1..*" Address : has

Complete the diagram by adding: Cart, CartItem, Order, OrderItem classes and their relationships.

Challenge Questions

• How do you represent that a Department has a "head" who is a Teacher?
• How do you show that Student and Teacher both inherit from Person?
• Is the Enrollment class really necessary, or can you just connect Student to Course?
• What interface might both Student and Course implement?

Starting Point (Mermaid)

Start with this basic structure and expand it:

classDiagram
    class Person {
        <<abstract>>
        -String name
        -Date birthdate
        -String email
    }

    class Student {
        -String studentId
        -Date enrollmentDate
        -double gpa
    }

    class Teacher {
        -String employeeId
        -Date hireDate
        -double salary
        -String specialization
    }

    class Course {
        -String code
        -String name
        -int credits
        -int maxCapacity
    }

    class Department {
        -String name
    }

    class Enrollment {
        -String grade
    }

    class Schedulable {
        <<interface>>
        +getSchedule() Schedule
    }

    Person <|-- Student
    Person <|-- Teacher

Complete the diagram by adding: relationships between Teacher/Course, Department connections, and the Enrollment association class.