Why can't an abstract class have a protected constructor?

[frankoverip]

I created several classes that represent the different kinds of business partners we have in our system. All classes shall be instantiated only by a factory class, so they shall only have protected constructors.

I created an abstract class on top of the hierarchy that provides some common attributes. For these attributes I have created a constructor.

My problem is now that I cannot set the constructor of my abstract class to protected. I get an error message saying that the visibility of the constructor must not be more special than the visibility of the instance creation.

As the class is an abstract class there is no instance creation. So, did I miss something? Is this just a bug or are there any reasons for this?

Best regards

Frank

[AndyBoolean]

Hi frankoverip,
So the constructor method must always be under the public section in ABAP.

CLASS zcl_gilded_rose DEFINITION
PUBLIC
ABSTRACT  
CREATE PUBLIC.
  PUBLIC SECTION.
    METHODS constructor.

  PROTECTED SECTION.  
  PRIVATE SECTION.
ENDCLASS.

You control who my instantiate the class via the CREATE PUBLIC ( PROTECTED / PRIVATE ) command.

Or do I not understand your question?

Regards
Andy

[frankoverip]

Hi Andy,

Thanks for your response. Although it did not really answer my question, it made me do some tests to prepare my answer. While doing so, it became clear to my why it is not problem that there is no protected constructor for abstract classes.

My error was that I expected a class inheriting a public constructor to become also public. But of course, this is not the case as I can still choose to allow only protected instantiation - which in a way makes the public constructor protected.

Thanks and regards

Frank