CS 4448 - Fall 1998
Object-Oriented Programming and Design
Talk 11.1

By

Brad Bailey

Towards the Clarification of the Object-Oriented Concepts

By

Dr Rose Mazhindu-Shumba

 

 

• Introduction: Dr. Shumba is a professor at the Department of Computer Science, University of Zimbabwe. This paper explores some definitions given by prominent researchers to explain and distinguish the more complex and closely related concepts of information hiding, abstraction and encapsulation. In addition we explain the concepts of classes and instances, polymorphism and dynamic binding and inheritance. The main goal of the paper is to try and clarify the often-confusing object-oriented concepts

The author accomplishes this task by dividing the above concepts into the following three groups:

• Concepts that appear during the analysis, design and implementation of a system; classes and instances and inheritance.
• Concepts that appear during the analysis and design of a system; these include data abstraction , encapsulation, and information hiding.
• Concepts that appear during the implementations of the system; these include polymorphism and dynamic binding

• Analysis and Design Concepts:

Abstraction, information hiding, and encapsulation are the three concepts that appear during the analysis and design of a system.

Abstraction - Abstraction draws a line around an object, where inside the boundary are the necessary characteristics of the object. By defining a boundary we can correctly define an object so that we can focus our attention on the real issues and not be diverted by unnecessary details.

Information Hiding - Information hiding is the principle stipulating that users of a software component need to know only the essential details of how to utilize a access the component.

Encapsulation- Encapsulation is a way of packaging information in such a way as to hide what should be hidden and make visible what is intended to be made visible.

• Analysis, design and Implementation Concepts:

Classes and Instances - A class describes a set of entities, which can be real or abstract.

Inheritance - Inheritance is a relationship between classes where one class is the parent (base, superclass, ancestor) class of another.

Two basic ways of using inheritance:

• Interface inheritance
• Implementation Inheritance

Types of Inheritance:

• Part Inheritance - occurs when an object changes its behavior by accepting new parts from other objects.
• Scope Inheritance - involves cases where the object's behavior is determined in part by the environment or its acquaintances.
• Monotonic Inheritance - is a variation of class inheritance whereby a child class inherits each and every property from its ancestor class.
• Partial Inheritance - properties inherited by the subclass may be dropped so that they are no longer properties of the child class.

• Implementation concepts:

Polymorphism and dynamic binding - Polymorphism means to take many forms. In object-oriented programming this refers to the ability of an entity to refer at run time to instances of various classes.

Two forms or polymorphism:

• Inclusion - directly implemented by inheritance

• Operation - operations with the same name can be applied to different objects that have no relation in terms of inclusion.

• Conclusion

Using the concepts of abstraction, information hiding and encapsulation to come up with well-designed classes will help to provide modular decomposition of a system as well as many other qualities expected of reusable software components. These concepts alone however are not enough to achieve the goals of reusability and extensibility. Inheritance is the feature that links the above concepts with the qualities expected of reusable software components. Full use of inheritance requires the cooperation of the concepts, information hiding, encapsulation, abstraction, and polymorphism.

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Revised: Novemeber 10, 1998