Chapter 2 Object Orientation

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Chapter 2Object Orientation
2
Process Phase Affected by This Chapter
Requirements Analysis
Design
Architecture
Framework
Detailed Design
Implementation
Key
less so
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permission.
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Before Object Orientation
Real world concepts
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Software Design Entities
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How Do We Express Ourselves?
"Customers Montague and Susan entered the Ajax
bank and were served by teller Andy ..... "
AJAX BANK
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How We Express Ourselves
"Customers Montague and Susan entered the Ajax
bank and were served by teller Andy ..... "
CLASSES
OBJECTS
Note that Java code convention reverses this
capitalization.
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Object Orientation
Real world concepts
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Direct correspondence
Account getDetails()
Transaction execute()
Customer getFirstName()
Software design entities
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permission.
Graphics reproduced with permission from Corel.
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Key Concept ? Benefits of OO ?
Object orientation provides a direct mapping
between concepts and code.
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Class Introduction
Real world
Class in Design (UML notation)
Class in Source code (Java)
class AjaxCustomer . . . .
AjaxCustomer
class PermissionToPay . . . .
Mental concept
PermissionToPay
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The Members of a Class
Objects of Auto
Non-static variable One version for every object
Class model
aliceBrownBMWAuto
Auto public int vehicleID protected int mileage
private myPrivateVariable static int
numAutosMade
33024
mileage
12390924850984
Static variable One version only
numAutosMade
Subclasses have these members too
myToyotaToyota
jaynesCarAuto
2105
83402
mileage
mileage
Toyota

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Attribute Types (Shlaer Mellor)

• Naming
• fixed for each object
• distinguishes individuals
• Descriptive
• varies through life of object
• Referential
• ties instance of one class to instance(s) of
  another
• aggregation

Auto vehicleID mileage owner
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Key Concept ? Classes and Objects ?
A class expresses a concept such as HondaCivic.
An object is an instance of a class such as the
Honda Civic with vehicle ID 89R783HJD894.
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The Clients of a Class
class Customer . . . String getName()
int computeBalance() . . .
Class Customer
class AjaxAssets . . . int computeAssets()
. . . Customer c customers i
assets c.computeBalance() .
. . . . .
class AjaxWebsiteGenerator . . . void
makeProfile( Customer c ) String
name c.getName() . . .
Client of Customer
Client of Customer
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Aspects of OO Useful for Application Development

• Class Introduction (section 2.2.1)
• basic motive of Object Orientation
• identifying parts that corresponds to the real
  world
• Instantiation (section 2.2.2)
• creating instances of encapsulated concepts
• Inheritance (section 2.3.1)
• capturing the way concepts occur in hierarchy
• Polymorphism (section 2.3.2)
• capturing use of single action word to represent
  different things, depending on context

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Requirements For e-Mail Creation Example

• 1. Summary
• Produces e-mail text for various types of
  customers.
• 2. Detailed requirements
• 2.1 The application displays choices to the
  console, as shown in figure xx.
• 2.2 For customers delinquent more than 90 days,
  the e-mail message generated is the statement
  shown in figure xx.

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Typical Interaction for e-mail Creation Example
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Requirements For e-Mail Creation Example
Page 3 of 4

• 2.3 All non-delinquent customers receive a
  tailored e-mail messages as follows. 
• 2.3.1 Mountain customers
• This month we have a special on West Face tents.
  Only 700.
• ... lots more output specialized to
  mountaineering customers ...
• 2.3.2 Regular customers
• All items are marked down 20 for this month
  only.
• ... lots more output for regular customers ...

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Requirements For e-Mail Creation Example
Page 4 of 4

• 2.4 The e-mail is to be displayed on the console.
• 3. Future enhancements
• We anticipate that the text is likely to change
  frequently, and that new kinds of customers are
  likely to be specified, each with its own new set
  of requirements.

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Disadvantages of Branching

• Code for each case not cohesive
• (cohesive forms a comprehensible unity)
• All types of customers coded together in single
  class
• Expensive to
• add new functionality
• bloat switch or if - then code
• remove functionality
• hunt for all parts that must be removed
• change functionality
• hunt for all parts that must be changed

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Aspects of the Customer Design Needing Improvement

• We need to visualize the design
• Code not an effective way to understand design
• The designs maintainability still has flaws
• As the application grows, specialized class(es)
  will be required to interact with the user

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Key Concept ? Polymorphism ?
- the use of several versions of a method, one in
each derived class. This enables
objectOfBaseClass.theMethod() to be interpreted
variously at runtime, depending on what derived
class objectOfBaseClass belongs to.
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Whats Needed to Specify Functionality

• Name of the function
• Example add
• Argument types(if any)
• Example
• First parameter integer
• Second parameter float
• Return type
• Example double, reference type, void
• Exceptions (if any)
• Example IOException
• More(?)
• Are parameters inputs and/or outputs?
• Describe what the function does (natural language)

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The Need For Interfaces Simplify
class Draw int setColor( String )
Pen getStandardPen() int getLogoStyle()
void setColor( int ) void drawLogo(
int, int ) void speedUpPen( int )
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Interface Example a Draw Class

• Functions dealing with the pen used
• Pen getStandardPen()
• void speedUpPen( int )
• . . .
• Functions dealing with the colors available
• void setColor( int )
• int setColor( String )
• . . .
• Functions covering the drawing of the companys
  logo
• void drawLogo( int, int )
• int getLogoStyle()
• . . .
• . . .. . . .

Pen interface

Color interface

Logo interface
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Key Concept ? Interfaces ?
An interface is a set of function prototypes
(each with name, parameter types, return type,
exception type).
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Issues to be Addressed

• How do we visualize a set of classes?
• How can classes relate to each other?
• How should classes relate to each other?
• How can we describe functionality occurring among
  several classes?
• How do we describe the manner in which objects
  respond to events occurring on them?
• Are there patterns of class usage that recur?
• So we can existing design parts

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Summary of This Chapter

• A Class represents a concept
• Example House
• An Object is an instance of a class
• Example 23 Main Street, Springfield
• Classes can relate in several ways Mainly
• A Client of a class refers to that class in one
  of its methods
• Inheritance kind of relationship
• Aggregation has a relationship, explained in
  chapter xx
• Polymorphism means action depends on context
• Executing anObject.aMethod() actually executes
  the version of aMethod() in the subclass that
  anObject belongs to

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permission.
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Typical Interaction for Auto Description Exercise
Adapted from Software Design From Programming to
Architecture by Eric J. Braude (Wiley 2003), with
permission.