Class Diagram

About

A Class Diagram is a structural UML (Unified Modeling Language) diagram that visually represents the blueprint of a system's classes, their attributes, methods, and relationships. It is widely used in object-oriented programming to design and document system architecture.

Refer to the official documentation for more details - https://plantuml.com/class-diagram

Elements of a Class Diagram

1. Classes

   • Represented as a rectangle with three sections:

     • Class Name (e.g., Customer)

     • Attributes (e.g., +name: String)

     • Methods (e.g., +getCustomerDetails(): String)

   • Example:

     +-----------------+
     |   Customer      |
     +-----------------+
     | - id: int       |
     | - name: String  |
     | - email: String |
     +-----------------+
     | +getDetails()   |
     | +updateEmail()  |
     +-----------------+

2. Relationships

   • Defines how classes interact with each other.

   • Association (--): Direct connection between classes.

   • Aggregation (<>--): A whole-part relationship where the part can exist independently.

   • Composition (*--): A stronger form of aggregation; the part cannot exist independently.

   • Inheritance (<|--): Denotes that one class is a subtype of another.

   • Dependency (..>): A weak relationship where one class depends on another.

3. Modifiers

   • Public (+): Accessible from anywhere.

   • Private (-): Accessible only within the class.

   • Protected (#): Accessible within the class and its subclasses.

   • Package (~): Accessible within the same package.

1. Banking System

This diagram represents a Banking System, including multiple relationships such as inheritance, composition, aggregation, and dependencies.

• Inheritance (<|--): SavingsAccount and CurrentAccount inherit from Account.

• Association (--): Customer owns multiple Accounts.

• Composition (o--): Bank is composed of multiple Accounts.

• Multiplicity (0..*, 1): Defines relationships between classes.

@startuml
title Banking System Class Diagram

class Account {
  - accountNumber: String
  - balance: double
  + deposit(amount: double)
  + withdraw(amount: double)
}

class SavingsAccount {
  - interestRate: double
  + addInterest()
}

class CurrentAccount {
  - overdraftLimit: double
  + checkOverdraft()
}

class Transaction {
  - transactionId: String
  - amount: double
  - date: Date
  + execute()
}

class Customer {
  - name: String
  - email: String
  - phoneNumber: String
  + getDetails()
}

class Bank {
  - name: String
  - branch: String
  + openAccount(customer: Customer)
  + closeAccount(account: Account)
}

Account <|-- SavingsAccount
Account <|-- CurrentAccount
Customer "1" -- "0..*" Account : owns
Account "1" o-- "*" Transaction : has
Bank "1" o-- "*" Account : manages

@enduml

2. Hospital Management System

This represents relationships between classes in a Hospital Management System.

@startuml
title Hospital Management System - Object Relationship Diagram

class Doctor {
    +name: String
    +specialization: String
}

class Patient {
    +name: String
    +age: int
}

class Appointment {
    +date: Date
    +time: Time
}

Doctor "1" -- "0..*" Appointment : schedules
Patient "1" -- "0..*" Appointment : books

@enduml