chapter one the object-oriented paradigm ku-yaw chang [email protected] assistant professor,...

Chapter OneChapter One

The Object-Oriented ParadigmThe Object-Oriented Paradigm

Ku-Yaw ChangKu-Yaw [email protected]@mail.dyu.edu.tw

Assistant Professor, Department of Assistant Professor, Department of Computer Science and Information EngineeringComputer Science and Information Engineering

Da-Yeh UniversityDa-Yeh University

22Ku-Yaw ChangKu-Yaw Chang The Object-Oriented ParadigmThe Object-Oriented Paradigm

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OverviewOverviewBefore the Object-Oriented Paradigm: Functional Before the Object-Oriented Paradigm: Functional DecompositionDecompositionThe Problem of RequirementsThe Problem of RequirementsDealing with Changes: Using Functional DecompositionDealing with Changes: Using Functional DecompositionDealing with Changing RequirementsDealing with Changing RequirementsThe Object-Oriented ParadigmThe Object-Oriented ParadigmObject-Oriented Programming in ActionObject-Oriented Programming in ActionSpecial Object MethodsSpecial Object MethodsSummarySummary


OverviewOverview

Object-Oriented ParadigmObject-Oriented Paradigm Compare and contrast withCompare and contrast with

Standard Structured ProgrammingStandard Structured Programming

ContentsContents Functional decompositionFunctional decomposition Problem of requirementsProblem of requirements Object-oriented paradigmObject-oriented paradigm Special object methodsSpecial object methods Important object terminologyImportant object terminology


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OverviewOverviewBefore the Object-Oriented Paradigm: Before the Object-Oriented Paradigm: Functional DecompositionFunctional DecompositionThe Problem of RequirementsThe Problem of RequirementsDealing with Changes: Using Functional Dealing with Changes: Using Functional DecompositionDecompositionDealing with Changing RequirementsDealing with Changing RequirementsThe Object-Oriented ParadigmThe Object-Oriented ParadigmObject-Oriented Programming in ActionObject-Oriented Programming in ActionSpecial Object MethodsSpecial Object MethodsSummarySummary


Functional DecompositionFunctional Decomposition

A natural way to deal with complexityA natural way to deal with complexity

Example: Example: You are given a task to write code to You are given a task to write code to Access a description of shapes that were Access a description of shapes that were

stored in a databasestored in a database Display shapesDisplay shapes



It would be natural to think in terms of the It would be natural to think in terms of the steps required:steps required:

1.1. Locate the list of shapes in the database.Locate the list of shapes in the database.

2.2. Open up the list of shapes.Open up the list of shapes.

3.3. Sort the list according to some rules.Sort the list according to some rules.

4.4. Display the individual shapes on the Display the individual shapes on the monitor.monitor.



Further break down Step 4.Further break down Step 4.1.1. Locate the list of shapes in the database.Locate the list of shapes in the database.

2.2. Open up the list of shapes.Open up the list of shapes.

3.3. Sort the list according to some rules.Sort the list according to some rules.

4.4. Display the individual shapes on the monitor.Display the individual shapes on the monitor.a)a) Identify type of shape.Identify type of shape.

b)b) Get location of shape.Get location of shape.

c)c) Call appropriate function that will display shape, Call appropriate function that will display shape, giving it the shape’s location.giving it the shape’s location.



A natural way to deal with complexityA natural way to deal with complexity Break down (decompose) the problem into Break down (decompose) the problem into

the functional steps that compose it.the functional steps that compose it.

ChallengeChallenge Not help us prepare the code for possible Not help us prepare the code for possible

changes in the futurechanges in the futureDealing with change – a graceful evolutionDealing with change – a graceful evolution



Many bugs originate with changes to Many bugs originate with changes to code.code.

Change creates opportunities for mistakes Change creates opportunities for mistakes and unintended consequences.and unintended consequences.

Nothing you can do will stop change. But Nothing you can do will stop change. But you do not have to be overcome by it.you do not have to be overcome by it.

You can never get all of requirements from You can never get all of requirements from the user.the user.

Too much is unknown about the future – Too much is unknown about the future – things change.things change.


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The Problem of RequirementsThe Problem of Requirements

Requirements from users areRequirements from users are IncompleteIncomplete Usually wrongUsually wrong MisleadingMisleading Do not tell the whole storyDo not tell the whole story

Requirements always change.Requirements always change. A bad thingA bad thing Few write their code to handle changing Few write their code to handle changing

requirementrequirement


The Problem of RequirementsThe Problem of Requirements

Requirements change for a very simple set of Requirements change for a very simple set of reasons:reasons: The users see new possibilities for the software after The users see new possibilities for the software after

discussions with developers.discussions with developers. Developers become more familiar with users’ problem Developers become more familiar with users’ problem

domain.domain. The environment in which the software is being The environment in which the software is being

developed changes.developed changes.

Must write our code to accommodate changeMust write our code to accommodate change Not give up on gathering good requirementsNot give up on gathering good requirements


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Dealing with Changes:Dealing with Changes:Using Functional DecompositionUsing Functional DecompositionUsing modularity to contain variationUsing modularity to contain variation

Make code more modularMake code more modular

Step 4c of displaying shapesStep 4c of displaying shapes Call appropriate function that will display shape, giving it the Call appropriate function that will display shape, giving it the

shape’s locationshape’s location

function : display shapefunction : display shapeinput: type of shape, description of shapeinput: type of shape, description of shapeaction:action: switch (type of shape) switch (type of shape) case squarecase square: :

put display function for square hereput display function for square here case circlecase circle::

put display function for circle hereput display function for circle here


Problems with ModularityProblems with Modularity

May or may not be possible to have May or may not be possible to have a a consistent descriptionconsistent description of shapes that will of shapes that will work for all shapeswork for all shapesModularityModularity Make the code more understandableMake the code more understandable Understandability Understandability

Make the code easier to maintainMake the code easier to maintain Does not deal with all of the variation it might Does not deal with all of the variation it might

encounterencounter


Low Cohesion and Tight CouplingLow Cohesion and Tight Coupling

CohesionCohesion How closely the operations in a routine are relatedHow closely the operations in a routine are related

CouplingCoupling The strength of a connection between two routinesThe strength of a connection between two routines

GoalGoal To create routines with internal integrity (To create routines with internal integrity (strong strong

cohesioncohesion) and small, direct, visible, and flexible ) and small, direct, visible, and flexible relations to other routines (relations to other routines (loose couplingloose coupling))


Unwanted Side EffectUnwanted Side Effect

Unwanted side effectUnwanted side effect Make a change to a function or piece of data in one Make a change to a function or piece of data in one

area of the codearea of the codeHave an unexpected impact on other pieces of codeHave an unexpected impact on other pieces of code

We really do not spend much time fixing bugs.We really do not spend much time fixing bugs. The overwhelming amount of time spent in The overwhelming amount of time spent in

maintenance and debugging is onmaintenance and debugging is onFinding bugsFinding bugs

Avoiding unwanted side effectsAvoiding unwanted side effects


Wrong FocusWrong Focus

Changes to one set of functions or data Changes to one set of functions or data impact other sets of functions and other impact other sets of functions and other sets of datasets of data In turn impact other functions that must be In turn impact other functions that must be

changedchangedLike a snowball that picks up snow as it rolls Like a snowball that picks up snow as it rolls downhilldownhill


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Dealing withDealing withChanging RequirementsChanging Requirements

How do people do thing?How do people do thing?ExampleExample

You were an instructor at a conferenceYou were an instructor at a conference People in your class had another class to attend People in your class had another class to attend

following yours, but didn’t know where it was located.following yours, but didn’t know where it was located.

Structured programming approachStructured programming approach1.1. Get list of people in the class.Get list of people in the class.2.2. For each person on this list:For each person on this list:

a.a. Find the next class they are takingFind the next class they are takingb.b. Find the location of that classFind the location of that classc.c. Find the way to get from your classroom to the person’s Find the way to get from your classroom to the person’s

next classnext classd.d. Tell the person how to get to their next classTell the person how to get to their next class


Dealing withDealing withChanging RequirementsChanging Requirements

Require following proceduresRequire following procedures1.1. A way of getting the list of people in the classA way of getting the list of people in the class2.2. A way of getting the schedule for each person in the A way of getting the schedule for each person in the

classclass3.3. A program that gives someone directions from your A program that gives someone directions from your

classroom to any other classroomclassroom to any other classroom4.4. A control program that works for each person in the A control program that works for each person in the

class and does the required steps for each personclass and does the required steps for each person

Would you actually follow this approach?Would you actually follow this approach? Post directions in the back of the roomPost directions in the back of the room Expect everyone would know what their next class Expect everyone would know what their next class

waswas


DifferenceDifference

First caseFirst case Give Give explicit directionsexplicit directions to everyone. to everyone. No one other than you is responsible for anything.No one other than you is responsible for anything.

Second caseSecond case Give Give general instructionsgeneral instructions Each person figure out how to do the task himself or Each person figure out how to do the task himself or

herselfherself

Shift of responsibilityShift of responsibility The same thing must be implemented.The same thing must be implemented. The organization is very different.The organization is very different.


The ImpactThe Impact

New requirementsNew requirements Give special instructions to graduate students Give special instructions to graduate students

who are assisting at the conferencewho are assisting at the conferenceCollect course evaluationsCollect course evaluations

Take them to the conference office before going to Take them to the conference office before going to the next classthe next class


Why the DifferenceWhy the Difference

First case First case Modify the control program to distinguish the graduate Modify the control program to distinguish the graduate

students from the undergraduatesstudents from the undergraduates Give special instructions to the graduate studentsGive special instructions to the graduate students

Modify the program considerablyModify the program considerably

Second caseSecond case Write an additional routine for graduate students to Write an additional routine for graduate students to

followfollow Control program remains the sameControl program remains the same

Significant differenceSignificant difference Control programControl program


What Makes It HappenWhat Makes It Happen

The people are responsible for themselvesThe people are responsible for themselves Instead of the control program being Instead of the control program being

responsible for themresponsible for them

The control program can talk to different The control program can talk to different types of people as if they were exactly the types of people as if they were exactly the samesame

The control program does not need to The control program does not need to know about any special stepsknow about any special steps


Perspectives in the Perspectives in the Software Development ProcessSoftware Development Process

ConceptualConceptual The concepts in the domain under studyThe concepts in the domain under study With little or no regard for the software that With little or no regard for the software that

might implement itmight implement it

SpecificationSpecification Look at the interface of the software, not Look at the interface of the software, not

implementationimplementation

ImplementationImplementation Look at the code itselfLook at the code itself


How Perspectives HelpHow Perspectives Help

Conceptual levelConceptual level Go to your next classGo to your next class What to do, not how to doWhat to do, not how to do

Implementation levelImplementation level The way they go to their classThe way they go to their class

Communicating at one level (conceptually) while Communicating at one level (conceptually) while performing at another level (implementation)performing at another level (implementation) The requestor (the instructor) does not know exactly The requestor (the instructor) does not know exactly

what is happeningwhat is happeningOnly know conceptually what is happeningOnly know conceptually what is happening


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Centered on the concept of the objectCentered on the concept of the object

ObjectObject Data with methodsData with methods

Data (Attributes) can be simple things like number Data (Attributes) can be simple things like number or character strings, or they can be other objectsor character strings, or they can be other objects

Define things that are responsible for Define things that are responsible for themselvesthemselves

Data: to know what state it is inData: to know what state it is in

Method (Code): to function properlyMethod (Code): to function properly


Objects and Their ResponsibilitiesObjects and Their Responsibilities

This Object…This Object… Is Responsible ForIs Responsible For

StudentStudent

Knowing which classroom they are inKnowing which classroom they are in

Know which classroom they are to go to nextKnow which classroom they are to go to next

Going from one classroom to the next classroomGoing from one classroom to the next classroom

InstructorInstructor Telling people to go to next classroomTelling people to go to next classroom

ClassroomClassroom Having a locationHaving a location

Direction GiverDirection Giver Given two classrooms, giving directions from one Given two classrooms, giving directions from one classroom to the otherclassroom to the other


How to Think About ObjectsHow to Think About Objects

ObjectsObjects Something with responsibilitiesSomething with responsibilities

A good design ruleA good design rule Objects should be responsible for themselves Objects should be responsible for themselves

and should have those responsibilities clearly and should have those responsibilities clearly defineddefined


How to Think About ObjectsHow to Think About Objects

At the conceptual levelAt the conceptual level An object is a set of responsibilitiesAn object is a set of responsibilities

At the specification levelAt the specification level An object is a set of methods that can be An object is a set of methods that can be

invoked by other objects or by itselfinvoked by other objects or by itself

At the implementation levelAt the implementation level An object is code and dataAn object is code and data


Public InterfacePublic Interface

Many methods of an object will be identified as Many methods of an object will be identified as callable by other objects.callable by other objects.

The collection of these methods is called the The collection of these methods is called the object’s object’s public interfacepublic interface StudentStudent object with the method gotoNextClassroom() object with the method gotoNextClassroom() More kinds of studentsMore kinds of students

Inefficient for each student type to have its own set of Inefficient for each student type to have its own set of methodsmethods

A more efficient approachA more efficient approach A general student to contain common methodsA general student to contain common methods Be used or tailored to their needsBe used or tailored to their needs



A class is a definition of the behavior of an A class is a definition of the behavior of an object, containing a complete description ofobject, containing a complete description of The data elements the object containsThe data elements the object contains The methods the object can doThe methods the object can do The way these data elements and methods can be The way these data elements and methods can be

accessedaccessed

Objects are Objects are instancesinstances of classes of classes Creating instances of a class is called Creating instances of a class is called instantiationinstantiation Each object of the same typeEach object of the same type

Different data, but have the same functionalityDifferent data, but have the same functionality


Go to the Next ClassroomGo to the Next Classroom

1.1. Start the control programStart the control program2.2. Instantiate the collection of students in the classroomInstantiate the collection of students in the classroom3.3. Tell the collection to have the students go to their next Tell the collection to have the students go to their next

classclass4.4. The collection tells each students to go to their next The collection tells each students to go to their next

classclass5.5. Each studentEach student

Finds where his next class isFinds where his next class is Determines how to get thereDetermines how to get there Goes thereGoes there

6.6. DoneDone


The Need for an Abstract TypeThe Need for an Abstract Type

The dilemmaThe dilemma Allow any type of student into the collectionAllow any type of student into the collection The collection is an array or something of some type The collection is an array or something of some type

of objectof objectRegularStudentRegularStudentGraduateStudentGraduateStudent

The solutionThe solution A general type that encompasses more than one A general type that encompasses more than one

specific typespecific typeStudent : an Student : an abstract classabstract class

RegularStudentRegularStudent GraduateStudentGraduateStudent


Abstract ClassAbstract Class

Abstract class define what other, related Abstract class define what other, related classes can do.classes can do. These “other” classes represent a particular These “other” classes represent a particular

type of related behavior.type of related behavior. Such a class is often called a Such a class is often called a concrete classconcrete class..

The abstract class is StudentThe abstract class is Student Concrete classes are RegularStudent and Concrete classes are RegularStudent and

GraduateStudentGraduateStudentRegularStudent is one kind of StudentRegularStudent is one kind of StudentGraduateStudent is one kind of StudentGraduateStudent is one kind of Student


Abstract ClassAbstract Class

InheritanceInheritance An An is-ais-a relationship relationship

RegularStudent class inherits from StudentRegularStudent class inherits from Student Derives fromDerives from SpecializesSpecializes A A subclasssubclass of of

Student class is the base class of Student class is the base class of GraduateStudent and of RegularStudentGraduateStudent and of RegularStudent GeneralizesGeneralizes A A superclasssuperclass of of


Abstract Class Abstract Class

Placeholders for other classesPlaceholders for other classes Define the methods their derived classes must Define the methods their derived classes must

implementimplement Contain common methods that can be used Contain common methods that can be used

by all derivationsby all derivations

Controller contains StudentsController contains Students The collection only needs to deal with The collection only needs to deal with

StudentsStudents Each kind of Student is left to implement its Each kind of Student is left to implement its

functionality in its own wayfunctionality in its own way


VisibilityVisibility

PublicPublic Anything can see itAnything can see it

ProtectedProtected Only objects of this class and derived classes Only objects of this class and derived classes

can see itcan see it

PrivatePrivate Only objects from this class can see itOnly objects from this class can see it


Encapsulation and PolymorphismEncapsulation and Polymorphism

EncapsulationEncapsulation Hiding dataHiding data

In general, any kind of hidingIn general, any kind of hiding

PolymorphismPolymorphism Poly : manyPoly : many Morph : formMorph : form Different behaviorDifferent behavior

Depend upon the specific type of derived objectDepend upon the specific type of derived object


Review of OO TerminologyReview of OO Terminology

ObjectObjectClassClassEncapsulationEncapsulationInheritanceInheritanceInstanceInstanceInstantiationInstantiationPolymorphismPolymorphismPerspectivesPerspectives


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New ExampleNew Example

Shape ExampleShape Example1.1. Locate the list of shapes in the databaseLocate the list of shapes in the database

2.2. Open up the list of shapesOpen up the list of shapes

3.3. Sort the list according to some rulesSort the list according to some rules

4.4. Display the individual shapes on the monitorDisplay the individual shapes on the monitor


Objects in Shape ProgramObjects in Shape Program

ShapeDataBaseShapeDataBase getCollection – get a specified collection of shapesgetCollection – get a specified collection of shapes

ShapeShape (an abstract class) (an abstract class) display – defines interface for Shapesdisplay – defines interface for Shapes getX – return X location of ShapegetX – return X location of Shape getY – return Y location of ShapegetY – return Y location of Shape

SquareSquare (derived from Shape) (derived from Shape) display – display a square (represented by this object)display – display a square (represented by this object)

CircleCircle (derived from Shape) (derived from Shape) Display – display a circle (represented by this object)Display – display a circle (represented by this object)


Objects in Shape ProgramObjects in Shape Program

CollectionCollection display – tell all contained shapes to display display – tell all contained shapes to display sort – sort the collection of shapessort – sort the collection of shapes

DisplayDisplay drawLine – draw a line on the screendrawLine – draw a line on the screen drawCircle – draw a circle on the screendrawCircle – draw a circle on the screen


Main ProgramMain Program

Create an instance of the database objectCreate an instance of the database object

Ask the database object to find the set of shapesAsk the database object to find the set of shapes Instantiate a collection object containing all of the Instantiate a collection object containing all of the

shapesshapes

Ask the collection to sort the shapesAsk the collection to sort the shapes

Ask the collection to display the shapesAsk the collection to display the shapes

The collection asks each shape to display itselfThe collection asks each shape to display itself

Each shape display itselfEach shape display itself


New RequirementsNew Requirements

Add new kinds of shapes (such as a Add new kinds of shapes (such as a triangle)triangle) Create a new derivation of Shape that defines Create a new derivation of Shape that defines

the shape.the shape. Implement a version of the display method Implement a version of the display method

that is appropriate for that typethat is appropriate for that type

Change the sorting algorithmChange the sorting algorithm Modify the method in Collection. Every shape Modify the method in Collection. Every shape

will use the new algorithmwill use the new algorithm


Encapsulation RevisitedEncapsulation Revisited

Using things is easierUsing things is easier User does not need to worry about User does not need to worry about

implementation issuesimplementation issues

Implementations can be changed without Implementations can be changed without worrying about the callerworrying about the caller

The insides of an object are unknown to The insides of an object are unknown to outside objectsoutside objects


BenefitsBenefits

The more I make my objects responsible The more I make my objects responsible for their own behaviors, the less the for their own behaviors, the less the controlling programs have to be controlling programs have to be responsible for.responsible for.Encapsulation makes changes to an Encapsulation makes changes to an object’s internal behavior transparent to object’s internal behavior transparent to other objects.other objects.Encapsulation helps to prevent unwanted Encapsulation helps to prevent unwanted side effectsside effects


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Special Object MethodsSpecial Object Methods

ConstructorConstructor A special method that is automatically called when the A special method that is automatically called when the

object is createdobject is created Handle starting up the objectHandle starting up the object

To eliminate uninitialized variablesTo eliminate uninitialized variables

DestructorDestructor A special method that helps an object clean up after A special method that helps an object clean up after

itself when the object is destroyeditself when the object is destroyed Release resourcesRelease resources JavaJava

Garbage collectionGarbage collection


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SummarySummary

Object orientation helps us minimize Object orientation helps us minimize consequences of shifting requirementsconsequences of shifting requirements In contrast with functional decompositionIn contrast with functional decomposition

Essential concepts and primary Essential concepts and primary terminology in object-oriented terminology in object-oriented programmingprogramming

The EndThe End

chapter one the object-oriented paradigm ku-yaw chang [email protected] assistant professor,...

Documents

list of shapes

functional steps

database display shapes

description of shapes

shapes location

individual shapes

changing requirements

graceful evolution slide