Class Diagram – Elevator System

A class diagram models the static structure of the system by showing classes, attributes, methods, and relationships between them. The Elevator System is a good example to demonstrate real-world object orientation including inheritance, composition, and associations.

Key Classes & Their Relationships

1. ElevatorSystem

Attributes:

• elevators: List<Elevator>
• controller: ElevatorController

Methods:

• requestElevator(floor: int, direction: Direction)
• step() // Advances system by one time unit

Relationships:

• Aggregates multiple Elevator objects.
• Delegates control logic to ElevatorController.

2. Elevator

Attributes:

• currentFloor: int
• direction: Direction (enum: UP, DOWN, IDLE)
• state: ElevatorState (enum: MOVING, STOPPED, DOOR_OPEN)
• floorQueue: Queue<int>

Methods:

• move()
• openDoor()
• closeDoor()
• addFloorRequest(floor: int)

Relationships:

• Composed inside ElevatorSystem.
• Communicates with Door and ButtonPanel.

3. ElevatorController

Attributes:

• elevators: List<Elevator>

Methods:

• assignElevator(floor: int, direction: Direction)
• optimizeRequests()

Responsibilities:

• Central logic that assigns which elevator should serve a floor request.

4. Floor

Attributes:

• floorNumber: int
• upButton: Button
• downButton: Button

Methods:

• pressUp()
• pressDown()

Relationships:

• Aggregated by ElevatorSystem.

5. Door

Attributes:

• isOpen: boolean

Methods:

• open()
• close()

Relationships:

• Composed by Elevator.

6. ButtonPanel

Attributes:

• buttons: Map<int, Button> // floor number to Button

Methods:

• pressButton(floor: int)

Relationships:

• Composed by Elevator.

7. Button

Attributes:

• isPressed: boolean

Methods:

• press()
• reset()

8. EmergencySystem

Attributes:

• isAlarmActive: boolean

Methods:

• triggerAlarm()
• stopAlarm()

Relationships:

• May be linked to Elevator or ElevatorSystem depending on design.

Optional Classes for Extensions:

• WeightSensor (to detect overload).
• MaintenanceMode (for technicians).
• AccessControl (for security-restricted floors).

Design Highlights for Students:

• Demonstrates composition (e.g., Elevator has Door, ButtonPanel).
• Shows aggregation (e.g., ElevatorSystem has multiple Elevators).
• Can explain state transitions using state and direction enums.
• Opens discussion on real-world modeling of asynchronous systems.