PlantUML Class Diagram: Inheritance and Interfaces

Class Diagrams with Inheritance in PlantUML

Class diagrams document the static structure of a system. They show classes, their attributes and methods, and the relationships between them.

Basic Class Definition

@startuml
class User {
  -id: UUID
  -email: String
  -passwordHash: String
  +login(email, password): Boolean
  +logout(): void
  #validateEmail(email): Boolean
}
@enduml

Visibility Modifiers

Symbol	Meaning
+	Public
-	Private
#	Protected
~	Package-private

Inheritance and Implementation

abstract class Shape {
  +area(): double
  +perimeter(): double
}

interface Drawable {
  +draw(canvas: Canvas): void
}

class Circle extends Shape implements Drawable {
  -radius: double
  +area(): double
  +perimeter(): double
  +draw(canvas: Canvas): void
}

The <|-- arrow represents inheritance (solid line, closed triangle). The ..|> arrow represents interface implementation (dashed line, closed triangle).

Relationship Types

Arrow	Relationship
<|--	Inheritance (extends)
..|>	Implementation (implements)
*--	Composition (strong ownership)
o--	Aggregation (weak ownership)
-->	Association (uses)
..>	Dependency (depends on)

Composition vs Aggregation

class Car {
  +start(): void
}
class Engine
class Passenger

Car *-- Engine : composition
Car o-- Passenger : aggregation

A car owns its engine (composition — engine cannot exist without the car), but contains passengers (aggregation — passengers exist independently).