Class Diagrams

Class diagrams show the structure of a system by depicting classes, their attributes, methods, and relationships.

Basic Class

E-commerce System

Design Patterns

Factory Pattern

Observer Pattern

Error generating PlantUML diagram: Request failed with status code 520

@startuml
interface Observer {
  +update(event: Event)
}

abstract class Subject {
  -List<Observer> observers
  +attach(observer: Observer)
  +detach(observer: Observer)
  +notify()
}

class ConcreteSubject extends Subject {
  -String state
  +getState(): String
  +setState(state: String)
}

class ConcreteObserver implements Observer {
  -String name
  +update(event: Event)
}

Subject o--> Observer : notifies
ConcreteSubject --> ConcreteObserver
@enduml

Advanced Relationships

Error generating PlantUML diagram: Request failed with status code 520

@startuml
class School {
  -String name
  -String address
}

class Department {
  -String name
  -String code
}

class Professor {
  -String name
  -String employeeId
}

class Student {
  -String name
  -String studentId
}

class Course {
  -String title
  -String code
  -int credits
}

' Composition: School "owns" departments
School "1" *-- "many" Department : has

' Aggregation: Department has professors
Department "1" o-- "many" Professor : employs

' Association: Professor teaches courses
Professor "1" -- "many" Course : teaches

' Many-to-many: Students enroll in courses
Student "many" -- "many" Course : enrolls

note right of School : Composition:\nDepartments cannot\nexist without School

note right of Department : Aggregation:\nProfessors can exist\nwithout Department
@enduml

Visibility Modifiers

• + Public
• - Private
• # Protected
• ~ Package/Internal

Relationship Types

• --|> Inheritance
• ..|> Interface implementation
• -- Association
• --> Directed association
• o-- Aggregation
• *-- Composition
• ..> Dependency