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Chapter 2: Approaches to S ystem Development : Object Orientation
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Chapter 2:
Approaches to System
Development :
Object Orientation
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Chapter 2
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
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Chapter 2
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
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Chapter 2
What Is a Class?
• A category of objects that share the same
attributes, operations, relationships, and
semantics
• All objects are instances of classes
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Chapter 2
Name
Attributes
Operations
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Chapter 2
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
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Chapter 2
Attributes are properties containing values
Minus sign
indicates
these are
private
(hidden)
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Chapter 2
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
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Chapter 2
Signature has
name, parameters,
return type
Methodimplements
the behavior
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Chapter 2
Plus sign
indicates
these are
public(accessible)
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Chapter 2
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
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Chapter 2
What Is Inheritance?
The mechanism by which the more specific
class in a generalization relationship
includes the attributes and operations of themore general class
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Chapter 2
Generalization
represented by
arrows from
subclass to
superclassSubclasses
inherit all
attributes and
operations of
superclasses
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Chapter 2
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
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Chapter 2
Here, eachtype of
vehicle has
its own
version of
calcPrice()
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Chapter 2
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
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Chapter 2
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
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Chapter 2
Interfaces arerepresented
as small
rectangles
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Chapter 2
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 partcan exist independently of the whole
– Compositions : part-whole relationships where the partand the whole are fully dependent on each other
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Chapter 2
This is a binary association, showing roles and multiplicities
roles
multiplicities
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Chapter 2
Systems Modeling
Systems modeling – creating an abstraction of a
system
Abstraction – focusing on the relevant aspects andignoring other details
UML is a modeling approach, involving these
diagrams:
– Use-case, sequence, communication, class, object,
activity, state, composite structure, package,
component, deployment
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Chapter 2
Unified Modeling Language
(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
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Chapter 2
Sample
UML
Diagram
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Chapter 2
UML Diagrams
Use-case diagram – shows use cases, actors, andrelationships describing user interactions withsystem
Sequence diagram – shows interactions of objectsvia message-passing in time-ordered manner
Communication diagram – similar to sequencediagram, but without the time-ordering
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Chapter 2
UML Diagrams
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
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Chapter 2
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
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Chapter 2
UML Diagrams (cont.)
Component diagram – shows software
components or modules and their
relationships
Deployment diagram – shows configuration
of runtime processing nodes and their components
