How To Fix OO121 - Constructors cannot be abstract (and are therefore implicitly final)

SAP Error Message - Details

• Message type: E = Error

• Message class: OO - Class Builder/API

• Message number: 121

• Message text: Constructors cannot be abstract (and are therefore implicitly final)

Self-Explanatory Message

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Smart SAP Assistant

• What is the cause and solution for SAP error message OO121 - Constructors cannot be abstract (and are therefore implicitly final) ?

  The SAP error message OO121, which states "Constructors cannot be abstract (and are therefore implicitly final)," typically occurs in ABAP Object-Oriented programming when you attempt to declare a constructor method as abstract in a class definition. In ABAP, constructors are special methods that are called when an instance of a class is created, and they cannot be abstract because they need to be implemented to create an object.
  Cause:
  The error arises when you define a constructor method in a class and mark it as ABSTRACT. In ABAP, constructors must have a concrete implementation because they are responsible for initializing the object. Since abstract methods are meant to be implemented in subclasses, it doesn't make sense for a constructor to be abstract.
  Solution:
  To resolve this error, you need to remove the ABSTRACT keyword from the constructor method definition. Here’s how you can do it:
  
  Locate the Class Definition: Find the class where the constructor is defined.
  Modify the Constructor: Change the constructor definition by removing the ABSTRACT keyword.
  
  Example:
  If you have something like this:
  CLASS my_class DEFINITION.
    PUBLIC SECTION.
      METHODS: constructor ABSTRACT.
  ENDCLASS.
  You should change it to:
  CLASS my_class DEFINITION.
    PUBLIC SECTION.
      METHODS: constructor.
  ENDCLASS.
  Related Information:
  
  Constructors in ABAP: Constructors are defined using the METHODS keyword and are called automatically when an instance of the class is created. They can take parameters and are used to initialize the object's attributes.
  Abstract Methods: Abstract methods are defined in abstract classes and must be implemented in subclasses. They cannot be instantiated directly.
  Final Methods: In ABAP, methods that are marked as FINAL cannot be overridden in subclasses. However, constructors are implicitly final, meaning they cannot be abstract or overridden.
  
  Additional Tips:
  
  Always ensure that your class design adheres to the principles of object-oriented programming. If you need to enforce certain behaviors in subclasses, consider using abstract methods for other methods, but not for constructors.
  Review the ABAP documentation for more details on class definitions, constructors, and abstract methods to deepen your understanding of object-oriented programming in ABAP.