How To Fix OO128 - Interface &1 already contained in interface &2

SAP Error Message - Details

• Message type: E = Error

• Message class: OO - Class Builder/API

• Message number: 128

• Message text: Interface &1 already contained in interface &2

Self-Explanatory Message

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Smart SAP Assistant

• What is the cause and solution for SAP error message OO128 - Interface &1 already contained in interface &2 ?

  The SAP error message OO128, which states "Interface &1 already contained in interface &2," typically occurs during the definition or implementation of interfaces in ABAP Objects. This error indicates that you are trying to include an interface that is already part of another interface, which is not allowed in SAP's object-oriented programming model.
  Cause:
  
  Redundant Interface Inclusion: You are attempting to include an interface (let's call it Interface A) into another interface (Interface B), but Interface A is already included in Interface B. This redundancy is what triggers the error.
  Circular References: If there are circular references where interfaces are including each other, it can also lead to this error.
  Incorrect Interface Design: The design of the interfaces may not be following best practices, leading to unnecessary complexity and redundancy.
  
  Solution:
  
  Check Interface Definitions: Review the definitions of both interfaces involved. Ensure that you are not redundantly including the same interface multiple times.
  Remove Redundant Includes: If you find that Interface A is already included in Interface B, remove the redundant inclusion from the interface definition.
  Refactor Interfaces: If the design is complex, consider refactoring the interfaces to simplify their relationships and avoid redundancy.
  Use Inheritance: If applicable, consider using inheritance instead of including interfaces. This can help in reducing redundancy and improving the design.
  Documentation: Ensure that the design and relationships between interfaces are well documented to avoid confusion in the future.
  
  Related Information:
  
  Interface Definition: In SAP ABAP, an interface is a collection of method definitions that can be implemented by classes. Interfaces allow for polymorphism and can be used to define a contract for classes.
  Best Practices: When designing interfaces, aim for clear and concise definitions. Avoid circular dependencies and strive for a clean architecture.
  SAP Notes: Check SAP Notes and documentation for any specific guidelines or updates related to interface handling in your version of SAP.
  
  If you continue to face issues after following these steps, consider reaching out to your SAP support team or consulting the SAP community for further assistance.