A Class Diagram shows:

Objects (classes, interfaces)
Their attributes and methods
Relationships: inheritance, association, composition

In ABAP, it’s a way to visualize your Z-logic before you write it — or to explain it clearly during specs or reviews.

📌 When to Use Class Diagrams

Use Case	Why It Helps
Designing ABAP classes	Clarifies design before you code
Explaining object relationships	Shows structure at a glance
Documenting custom Z-logic	Clean, readable specs
CDS + OO hybrid logic	Show how objects consume views
Handover to other developers	Transfer knowledge visually

🧩 Class Diagram Notation in PlantUML

Element	Syntax Example	Meaning
Class	`class ZCL_HANDLER`	ABAP class
Interface	`interface IF_ORDER_CHECK`	ABAP interface
Attribute	`+ MATNR : MATNR`	Public field
Method	`+ check_order( )`	Public method
Inheritance	`class A extends B`	Classic inheritance
Interface Implementation	`class A implements B`	Implements interface
Composition	`A *-- B`	"Has-a" (class uses another)
Association	`A --> B`	Reference or collaboration

✅ Example: Simple Z-Logic Design

plantuml
CopyEdit
@startuml
title Class Diagram — ABAP Order Processing

class ZCL_ORDER_HANDLER {
  + process_order( )
  - validate_items( )
}

class ZCL_ORDER_LOGGER {
  + log_event( )
}

interface IF_ORDER_CHECK {
  + check_validity( )
}

ZCL_ORDER_HANDLER --> ZCL_ORDER_LOGGER : uses
ZCL_ORDER_HANDLER ..|> IF_ORDER_CHECK : implements

@enduml

What this shows:

One main handler class
A logger utility used via association
An interface being implemented for reusability

⚙️ Advanced Example: With Attributes and Data Types

plantuml
CopyEdit
@startuml
title ABAP Class with Attributes

class ZCL_MATERIAL_HANDLER {
  + MATNR : MATNR
  + process_material( )
  - fetch_data_from_db( )
}

@enduml

+ means public
means private
You can skip visibility if not relevant

🔧 Real-World Use

Let’s say you’re designing a small ABAP framework for handling material checks:

plantuml
CopyEdit
@startuml
title ABAP Class Framework — Material Checks

interface IF_CHECK {
  + execute( )
}

class ZCL_CHECK_MATERIAL implements IF_CHECK {
  + execute( )
  - read_mara( )
}

class ZCL_CHECK_SITE implements IF_CHECK {
  + execute( )
  - read_werks( )
}

class ZCL_CHECK_CONTROLLER {
  + run_all_checks( )
  - results : string[]
}

ZCL_CHECK_CONTROLLER --> IF_CHECK : runs

@enduml

You now have:

Multiple reusable check classes
One controller that runs all checks
Interface-based architecture = extensible

This is what good ABAP architecture looks like before it’s built.

🧠 Pro Tips

✅ Use class diagrams for custom frameworks, exit logic, Z-modules, and enhancements

✅ Combine with activity/sequence diagrams to show how objects interact

✅ Use in specs to align before coding starts

✅ Use stereotypes like <<interface>> or <<abstract>> if needed

✅ Summary

Class diagrams let you draw your design before you build it.

They help you think in objects, not just forms and tables.

Use them to:

Design better logic
Explain structure fast
Reuse patterns
Avoid messy procedural Z-monoliths

Next up:

👉 Visual SAP #6 — Use Case Diagrams: Who Does What in Your SAP Projects

We’ll map roles, actions, and systems — to clarify responsibility and access in a single diagram.

Visual SAP with plantUML #5 Class Diagrams