How To Fix OL665 - Interfaces cannot have subtypes

SAP Error Message - Details

• Message type: E = Error

• Message class: OL - Workflow object types: Run-time system

• Message number: 665

• Message text: Interfaces cannot have subtypes

What causes this issue?

You tried to create a subtype for an interface. However, interfaces
cannot have subtypes.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Firstly, create an object type and assign the specified interface to
the object type. The object type will then support this interface, i.e.
implement all the interface attributes and methods.

Error message extract from SAP system. Copyright SAP SE.

Smart SAP Assistant

• What is the cause and solution for SAP error message OL665 - Interfaces cannot have subtypes ?

  The SAP error message OL665, which states "Interfaces cannot have subtypes," typically occurs when you are trying to create a subtype of an interface in ABAP (Advanced Business Application Programming). In ABAP, interfaces are meant to define a contract for classes, and they cannot be extended or subclassed like regular classes.
  Cause:
  The error arises when you attempt to define a new interface that is a subtype of an existing interface. In ABAP, interfaces are not designed to support inheritance in the same way that classes do. This means you cannot create a hierarchy of interfaces where one interface is a subtype of another.
  Solution:
  To resolve this error, you should:
  
  
  Remove the Subtype Declaration: If you have mistakenly declared an interface as a subtype of another interface, you need to remove that declaration. Ensure that your interface is defined independently without any parent interface.
  
  
  Use Composition Instead: If you need to share functionality or methods between interfaces, consider using composition. You can define multiple interfaces and have classes implement multiple interfaces as needed.
  
  
  Refactor Your Design: If your design requires a hierarchy, consider whether you can achieve your goals using classes instead of interfaces. Classes can have superclasses and subclasses, allowing for inheritance.
  
  
  Check for Misunderstandings: Ensure that you understand the purpose of interfaces in ABAP. They are meant to define a set of methods that implementing classes must provide, rather than to create a hierarchy.
  
  
  Related Information:
  
  ABAP Interfaces: Interfaces in ABAP are used to define a set of methods that can be implemented by classes. They are useful for achieving polymorphism and defining contracts for class behavior.
  Inheritance in ABAP: While interfaces cannot have subtypes, classes can inherit from other classes. This is a key feature of object-oriented programming in ABAP.
  Documentation: Refer to the official SAP documentation on ABAP Object-Oriented Programming for more details on interfaces and their usage.
  
  By following these guidelines, you should be able to resolve the OL665 error and design your ABAP code correctly.