Virtual

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The modifier virtual:

  • belongs to object-oriented programming;
  • describes a virtual method.

A virtual method must also be implemented (programmed) in the class in which it was declared.

A virtual method can be overwritten in a derived class with the reserved word override.

If a virtual method is to be hidden, the class must be covered with the reserved word Reintroduce.

Example:

 Type
   TBody = class
   private
     dblHeight : double;
   public
     function volume : double; virtual;     // This method can be in one of this class
                                            // derived class can be hidden or overwritten
     function surfaceArea double; virtual;  // This method must be in one of this class
                                            // derived class can be hidden or overwritten
 end;