Object-Oriented Development Concepts

Slides by Emmanuel Owusu-Oware, CAD, UGBS

Lecture by: Dr. Boateng Email: Richard@pearlrichards.org

Learning Objectives

Understanding of Object-Oriented concepts/terminologies

Introduction to Unified Modelling Language (UML)

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Introduction

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Introduction

Object Oriented Development (OOD) presents a different perspective, philosophy, mindset to software development: View of applications as objects Objects do things: behaviour , methods, Objects have things: attributes or characteristics Example: A traffic light

Object: A traffic lightCharacteristic: Colour [Red, Yellow, Green]Behaviour: Turn_red

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Introduction

Object-Oriented Development vs. Process-Oriented/ Structured Development: The Difference

OOD SD1. Focus is on Objects, their associated Data and the Actions they perform.

2. The software is modelled on the following elements of objects:•Characteristics/Attributes /Properties•Behaviors /Operations /Methods•Relationships/Associations

1. Focus is on functionality

2. The software is modelled on the following elements

Data Functions and proceduresFunctional decomposition / modularization

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Introduction

OOD Strengths Easier Development

OOD uses a model that have closer representation of real-world situations

OOD uses smaller independent units Maintainability – quicker and easier

changes affecting an object will not require change to other parts of the software

A fault could be identified with the object that is responsible

OOD uses smaller independent units

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IntroductionOOD Strengths (contd.) Rapid application development, i.e. shorter

development life-cycle Through the reuse of object implementations Shorter life-cycle - Schach (2002) (see next slide)

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Introduction

OOD WeaknessOne weakness that OOD had was that there was no universally accepted standards in development methodology and tools. This is no longer the case with the emergence and acceptance of UML (Unified Model language).

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Object-Oriented Development Concepts

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What is an Object?

Definition: An object is a self-contained unit with well-defined characteristics (properties or attributes) and behaviours (operations) – Tsang et al (2005).

Example: A student in a school. Object: A Student Attributes/Characteristics: Name, Age Behaviour/Operation: Writes exams

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Object Concepts The object behaviour is a set of operations that it

performs to meet the system goal. An operation is a function or procedure through

which other objects access an object’s data. The collection of operations is the object’s

interface. Other objects access the object’s operations through the interface

Example: The book class in the Library system have the operations :

borrow (book), return ( book), getBookStatus()

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Object Concepts An object has many states. It can be in one state at

a time. The state is represented by values of the properties or attributes:

Example: Book – [Borrowed, Available, On Order] Types of Objects

Domain Objects (real-world entities)Physical (Tangible): E.g. BookConceptual (Intangible): E.g. Bank Account

Implementation Objects (software object)E.g. : Transaction log file which is used for error

recovery

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A Class and Instance

Definition: A class is an abstraction of real-world entity that captures and specifies the properties and behaviours essential to the system but hides those that are irrelevant. - Tsang et al (2005).

A class is a generic definition for a set of similar objects.

An object is an instance of a class. A class has methods and attributes while object

instances have behaviours and states.

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A Class and Instance

An attribute is a property of a class. Attributes have a name and a value and may also

have a type e.g. Integer or Boolean. Illustration:

Class: Name: Book Properties: ISBN, Title, Author(s)

Instances: Title: Structured Engineering Title: Advance VB.Net Programming

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Inheritance, Generalisation and Specialisation Inheritance refers to the derivation of a new

class (sub-class) from an existing class (base or super-class).

Employee

Manager Clerk

Base class

Sub-class

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Inheritance, Generalisation and Specialisation

Through inheritance, the sub-class acquires all the attributes (properties) and methods of the base class in addition to its specialised properties and methods.

It also allows code reuse and thus faster application development and extensibility of the software system.

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Inheritance, Generalisation and Specialisation

Inheritance allows generalisation and specialisation associations :

Generalisation distributes the commonalities from the super class (general/bases class) among a group of similar sub-classes (specialised class). The subclass inherits all the super-class’s operations and attributes.

Specialisation allows subclasses to extend the functionalities of their super class by introducing new operations and attributes.

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Inheritance, Generalisation and Specialisation

Persons

Students Employees

Faculty Staff

Non-Teaching StaffTeaching staff

Superclass

Subclasses

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