Question

C++ Programming

1) What is the feature that makes a base class an abstract class?

2) When designing a class hierarchy involving classes A and B, what are the two questions that must be asked to determine whether class B should be derived from class A?

Answer 1

1) What is the feature that makes a base class an abstract class?

• An abstract category is, conceptually, a category that can't be instantiated and is sometimes enforced as a category that has one or additional pure virtual functions.
• A pure virtual perform is one that should be overridden by any concrete   derived category. This can be indicated within the declaration with the syntax " = 0" within the member function's declaration.
• In general associate degree abstract category is employed to outline associate degree implementation and is meant to be genetic from by concrete categories.
• It is a means of forcing a contract between the categories the designer and therefore the users of that class.
• If we tend to would like to form a concrete category from associate degree abstract category we tend to should declare and outline an identical member perform for every abstract member perform of the bottom category.
• This is one thing of a contrived example however it will show however that you just will share implementation details among a hierarchy of categories.
• Every category any refines an inspiration. This can be not perpetually the simplest thanks to implement associate degree interface however in some cases it works fine.
• As a suggestion, for simple maintenance and understanding you must attempt to limit the inheritance to no over three levels.
• Typically the simplest set of categories to use could be a pure virtual abstract base category to outline a typical interface.
• Then use associate degree abstract categories to any refine associate degree implementation for a collection of concrete categories and in conclusion outline the set of concrete categories.
• This should be resisted; generally it's a proof that the interface isn't well factored. Information and concrete member functions tend to imply a selected implementation and intrinsically will inherit from the interface however shouldn't be that interface.
• Instead if there's some commonality between concrete categories, creation of abstract category that inherits its interface from the pure abstract category and defines the common information and member functions of the concrete categories works well.
• Some care ought to be taken to come to a decision whether or not inheritance or aggregation ought to be used.
• Too several layers of inheritance will create the upkeep and usage of a category tough. Generally, the most accepted layers of inheritance are regarding three, on top of that and refactoring of the categories is usually involved. A general check is that the "is a" vs. "has a", as in an exceedingly sq. could be a parallelogram; however a sq. contains a set of sides.