2-1 © Prentice Hall, 2007 Chapter 2: Introduction to Object Orientation Object-Oriented Systems...

2-1© Prentice Hall, 2007

Chapter 2:Chapter 2:Introduction to Object Introduction to Object

OrientationOrientation

Object-Oriented Systems Analysis and Design

Joey F. George, Dinesh Batra,

Joseph S. Valacich, Jeffrey A. Hoffer

Chapter 2 2-2© Prentice Hall, 2007

Chapter ObjectivesChapter Objectives

After studying this chapter you should be able to:– Define an object.– Understand the terms class, attribute, and operations.

– Explain generalization, polymorphism, and inheritance.

– Define association.– Describe modeling and the Unified Modeling

Language.


Unified Modeling Language Unified Modeling Language (UML)(UML)

A standard notation for representing object-oriented systems

Boxes represent classes, components, packages, objects– Containing attributes and operations– Provide interfaces to external entities

Lines represent generalization and other relationships


Sample UML Diagram


What Is an Object?What Is an Object?

An entity that encapsulates data and behavior

- Objects are categorized into classes

- Each individual object is an instance of a class


What Is Encapsulation?What Is Encapsulation?

The characteristic of object-orientation in which data and behavior are bundled into a class and hidden from the outside world

Access to the data and behavior is provided and controlled through an object’s interface


What Is a Class?What Is a Class?

• A category of objects that share the same attributes, operations, relationships, and semantics

• All objects are instances of classes


Name

Attributes

Operations


What Is an Attribute?What Is an Attribute?

• Attribute- a named property of a class that describes a range of values that instances of the attribute might hold

• Attributes are the way classes encapsulate data


Attributes are properties containing values

Minus sign indicates these are private (hidden)


What Is an Operation?What Is an Operation?

A behavior of an object

Implemented in classes are methods

Methods are identified and invoked by their signatures, including name, parameters, and return type


Signature has name, parameters, return type

Method implements the behavior


Plus sign indicates these are public (accessible)


What Is Generalization?What Is Generalization?

A relationship between a more general (or parent) class and a more specific (or child) class

The more specific class has additional attributes and operations


What Is Inheritance?What Is Inheritance?

The mechanism by which the more specific class in a generalization relationship includes the attributes and operations of the more general class


Generalization represented by arrows from subclass to superclassSubclasses

inherit all attributes and operations of superclasses


What Is Polymorphism?What Is Polymorphism?

The ability for different classes of objects to respond to identical messages in different ways

Polymorphism = “having many forms”

Different behaviors for the same message


Here, each type of vehicle has its own version of calcPrice()


What Is a Component?What Is a Component?

A replaceable part of a system providing a clearly defined function through a set of interfaces

Group of classes working together toward a common end; a subsystem


What Is an Interface?What Is an Interface?

The mechanism by which users of a component invoke its behaviors and manipulate its properties

The interface is implemented by method signatures


Interfaces are represented as small rectangles


What Is a Package?What Is a Package?

A logical grouping of related analysis or design elements

Group of classes sharing similar characteristics or purposes


Package is to component as folder is to file


What Is an Association?What Is an Association?

A relationship or link between instances of (or objects) of classes

Three types:– Simple associations: no ownership– Aggregations: part-whole relationships where the part

can exist independently of the whole– Compositions: part-whole relationships where the part

and the whole are fully dependent on each other


This is a binary association, showing roles and multiplicities

roles

multiplicities


Systems ModelingSystems Modeling

Systems modeling – creating an abstraction of a system

Abstraction – focusing on the relevant aspects and ignoring other details

UML is a modeling approach, involving these diagrams:– Use-case, sequence, communication, class, object,

activity, state, composite structure, package, component, deployment


UML DiagramsUML Diagrams– Use-case diagram – shows use cases, actors, and

relationships describing user interactions with system– Sequence diagram – shows interactions of objects via

message-passing in time-ordered manner– Communication diagram – similar to sequence diagram, but

without the time-ordering– Class diagram – shows set of classes and relationships

(generalizations and associations)– Object diagram – shows specific instances of a class diagram– Activity diagram – shows flow of activities, or wokflow of

objects


UML Diagrams (cont.)UML Diagrams (cont.)

– State diagram – shows transitioning of an object from state to state in response to events

– Composite structure diagram – shows how a component whole is made up of its parts

– Package diagram – shows logical grouping of analysis or design elements

– Component diagram – shows software components or modules and their relationships

– Deployment diagram – shows configuration of runtime processing nodes and their components

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