Object Oriented Programming

(Updated: 2007.12.24 12:08:53 AM)

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Formally, from the Dictionary of Object Technology (Prentice Hall ISBN 0133738876

, SIGS Books ISBN 1884842097

), it is: n. any application-specific programming resulting in programs that consist of collections of collaborating objects, which have a unique identity, encapsulate properties and operations, communicate via message passing, any [sic?] are instances of classes related by inheritance, polymorphism, and dynamic binding. [Booch, Firesmith]"

Features of OOP:

Abstraction -- The ability to ignore the inner details and concentrate on the functionality exposed through the interface of the object.

Encapsulation -- The ability to group related pieces of information and processes into a self-contained unit. Encapsulation is implemented using:

Objects with Properties and Methods. These are referred to with the following notation: Object.Property, Object.Method()

Polymorphism -- The ability to send the same message to items of different types and have each respond in its own way. Polymorphism is implemented using:

Implementing Interfaces -- A class is defined formally as Implementing a specific Interface, which is a specific set of properties and methods. VFP7 now supports this method.
Classes and Subclasses -- By having two differing subclasses of the same parent class (the parent class defines the interface), any subroutine that expects the parent class should be able to operate on either subclass.
Ad-hoc Polymorphism -- In VFP, you can informally define an interface and implement it in unrelated classes, then hand any of these classes to a subroutine that requires the informally defined interface. This works in VFP because VFP is LooseTyped.

Inheritance -- The ability of an item to receive the characteristics of the item on which it was based. Inheritance is implemented using:

Classes and Subclasses -- Please see Super Class, Base Class, Parent Class, Sub Class

This is a great book that combines Object Oriented Programming with Visual FoxPro:

MarkusEgger (1999), Advanced Object Oriented Programmingwith Visual FoxPro 6.0, Hentzenwerke, Milwaukee, WI, ISBN 0965509389

Ivar Jacobson describes a good example of when object-orientation is/is-not a good approach. The example describes what types of solutions are/are-not suited for object-orientation. I found this example very useful to clarify what is object-oriented and what is not. Next time you are at the book store, pick up his book Object Oriented Software Engineering: A Use-Case driven approach ( ISBN 0201544350

) and take a look at pages 135-141.
-- Hector Correa

Links

OOP Criticism - http://www.geocities.com/tablizer/oopbad.htm