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Asked: 2026-05-10T21:37:18+00:00

I have an abstract class: type TInterfaceMethod = class abstract public destructor Destroy; virtual;

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I have an abstract class:

type   TInterfaceMethod = class abstract   public     destructor Destroy;         virtual; abstract;     function GetBasePlan: Word; virtual; abstract;     procedure CountBasePlan;    virtual; abstract;     procedure Calculate;        virtual; abstract;     procedure PrepareForWork;   virtual; abstract;   end;

and a derived class:

type   TFogelMethod = class(TInterfaceMethod)   private     matrix: TFogelMatrix;     BasePlan: Word;   public     constructor Create(var matr: TFogelMatrix);     procedure Calculate;     function GetBasePlan: Word;     procedure CountBasePlan;     procedure PrepareForWork;     destructor Destroy;   end;

The question is, can I place the implementation of GetBasePlan and CountBasePlan methods into base class, make them only virtual – not abstract as now – and also place member BasePlan there? So, can I do this:

type   TInterfaceMethod = class abstract   private    BasePlan: Word;   public     destructor Destroy;         virtual; abstract;     function GetBasePlan: Word; virtual;      procedure CountBasePlan;    virtual;      procedure Calculate;        virtual; abstract;     procedure PrepareForWork;   virtual; abstract;   end;

In case I can do it, will it be good from the point of view of object-oriented design, and how can I exactly access this member from derived classes?

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1 Answer

  1. Yes you can. Abstract classes are classes and they can have implementations.

    By adding the abstract keyword to a class, you prohibit the class to be instantiated. It does not require to have any abstract methods.

    A class with absract methods can be instantiated, but this result in a warning at compile time and an exception if the method is called.

    Interfaces have no implementation, they have to be implemented by classes (which can be abstract by the way).

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