chapter 3comp.mq.edu.au/books/rasd2ed/readersarea/lecturesli… · · 2008-12-07chapter 3.1...

MACIASZEK, L.A. (2005): Requirements Analysis and System Design, 2nd ed.

Addison Wesley, Harlow England, 504p.ISBN 0 321 20464 6

© Pearson Education Limited 2005

Chapter 3.1 Objects and Object Modeling

Fundamentals of Object Technology

© Pearson Education 2005© Pearson Education 2005 Chapter 3.1 (Maciaszek Chapter 3.1 (Maciaszek -- RASD 2/e)RASD 2/e) 22

TopicsTopicsFundamentals of object

technology

• Instance object

• Class

• Variables, methods, and

constructors

• Association

• Aggregation and composition

• Generalization and

inheritance

• Abstract class

• Interface

Fundamentals of object

modeling

• Use case modeling

• Activity modeling

• Class modeling

• Interaction modeling

• Statechart modeling

• Implementation models


Fundamentals of OTFundamentals of OT

Object has

• State

• Behavior

• Identity

(equal ≠ identical)

Objects and natural systems


Instance objectInstance objectClass• an abstraction (generic description) for a set of

objects• a class for objects (but better to avoid the term

“object class” because a class can be instantiated into an object – “object class object’ would sound a bit strange)

Instance object• an instance of a class• object, instance, but not object instance

Class object• an instantiated class (everything in an object

oriented system is an object)


Object notationObject notation

c1 : Course

course_number = COMP227course_name = Requirements Analysis and Systems Design

c1 : Course :Course c1

objectname: classname attributename: [type] = value

No compartment for operations in objects!Exception – prototypical (delegation-based) languages, such as Self or Newton

anonymous object classname suppressed


How do objects collaborate?How do objects collaborate? : Order

: Shipment : Stock

: Purchase

3. analyzeLevels( )1 . shipOrder(ord : Order)

2. getProducts(ord : Order)

4. reorder(prd : Product)

a role that many objects can play

a message invoking an operation on an object(numbers do not imply any sequence of execution)


How objects identify each other?How objects identify each other?object identifier - OID

Object longevity• Persistent object

–– outlives the execution of the programoutlives the execution of the program

–– swizzlingswizzling to convert persistent OID (disk address) to transient OID to convert persistent OID (disk address) to transient OID (memory address)(memory address)

• Transient object

c1 : Course

course_number = COMP227course_name = Requirements Analysis and Systems Designteacher: identity = TTT999

CCC888c1 : Course

course_number = COMP227course_name = Requirements Analysis and Systems Designteacher: identity = TTT999

CCC888


OIDs to implement associationsOIDs to implement associations

c1 : Course

course_number = COMP227course_name = Requirements Analysis and Systems Design

c2 : Course

t1 : Teacher

coursecourse

teacher

teacher


Transient linkTransient linkHow does an object know the OID of another object

if there is no persistent link?

• Previous access to an object still “memorized” in some

program variable

• Search on the database

• A “map” object that associates objects to other objects by

logical identifiers (primary keys) or similar means

• Creating a new object


Message passingMessage passingcrs_ref.getCourseName(out crs_name)

in, out, and in/out arguments• Most OO languages do not make such distinction explicit• In Java:

–– message arguments of primitive data types are passed by valuemessage arguments of primitive data types are passed by value• act as input arguments• the change of argument values not possible because the operation acts

on a copy of the argument

–– “pass by value” for non“pass by value” for non--primitive data types results in the operation primitive data types results in the operation receiving the reference of the argument, not its valuereceiving the reference of the argument, not its value

• the reference can be used to access and possibly modify the attribute values within the passed object

• the above eliminates the need for explicit in/out arguments

–– return type of an operation substitutes a need for explicit return type of an operation substitutes a need for explicit out out argumentsarguments

• operation can return only one return value or no value at all (void)• however, it can return non-primitive type (i.e. an object of any complexity)


Class, attributesClass, attributesClas s nam e

Attributes

Operations ()

Orderorder_number : Int egerorder_date : Dateorder_value : Currency

Coursecourse_number : Stringcourse_name : String


Attribute type designating a classAttribute type designating a classShipment

shipOrder(ord : Order)

OrderorderNumber : IntegerorderDate : DateorderValue : Currency theShipment

theOrder

ShipmenttheOrder : Order


OrderorderNumber : IntegerorderDate : DateorderValue : CurrencytheShipment : Shipment

analysis model

implementation model


Attribute visibilityAttribute visibilityprivate attributes and public operationsoperations encapsulate attributes

Purchase- purchaseNumber : String- purchaseDate : Date- purchaseValue : Currency

+ reorder(prd : Product)

PurchasepurchaseNumber : StringpurchaseDate : DatepurchaseValue : Currency

reorder(prd : Product)


Operations in object collaborationOperations in object collaboration

Stock

getProducts(ord : Order) : CollectionanalyzeLevels()

Purchase

reorder(prd : Product)

Shipment


Order Product

: Order

: Shipment : Stock

: Purchase

3. analyzeLevels( )1 . shipOrder(ord : Order)

2. getProducts(ord : Order)

4. reorder(prd : Product)


Operation, visibility, scope, class objectOperation, visibility, scope, class objectmethod – procedure that implements an operationmessage name = method namesignature = list of formal arguments of a methodvisibility ≠ scope• instance scope when operation invoked on instance

object (findEmpAge())• class scope when operation invoked on class object

(findAverageAge())Class object• most prog. lang. do not instantiate class object• they only provide a syntax to refer to the class name in

order to access a class-scope attribute or call a class-scope operation → static attribute/operation

Example → next slide


ClassClass--scope attributes and operations scope attributes and operations -- exampleexampleStudent

studentId : S tringstudentName : S tringnumberOfS tudents : intmaxCoursesPerSemester : int

<<static>> averageStudentAge() : double

public class Student {

private String studentId; //accessible via Student’s operations private String studentName; //accessible via Student’s operationsprivate static int numberOfStudents;//accessible only to Student’s static methods, such as averageStudentAge() public static int maxCoursesPerSemester; //accessible via Student:: maxCoursesPerSemester

public static double averageStudentAge() { implementation code here }//callable by referring to the class name – Student::averageStudentAge()//callable also with an object of the class – std.averageStudentAge()

}


Variables, methods, constructorsVariables, methods, constructorsVariable – name for a storage space• data member – variable declared in a class

–– instance variable (instance scope)instance variable (instance scope)–– class variable (class scope)class variable (class scope)

• local variable – variable declared in a method bodyMethod – implementation of an operation• method prototype = name + signature + return type• overloaded methods – same names, different signatures

Constructor• special “method” to instantiate objects of the class• constructor name = class name• constructor has no return type• class must have at least one constructor• invoked with the new keyword

Student std22 = new Student(); Student std22 = new Student(); //default constructor//default constructor


AssociationAssociation

ShipmentshipmentId : StringshipmentDate : Datecarrier : String


OrderorderNumber : IntegerorderDate : DateorderValue : Currency

n

n

theShipment n

theOrder

n

OrdShip


Association degreeAssociation degreeBinary

Unary (singular)

Ternary

Employee0..n

0..1

managerOf

0..n

managedBy

0..1


Association multiplicityAssociation multiplicity0..10..n1..11..nn

CourseOffering

Teacher

0..n

1..nteaches

0..n

taughtBy

1..n

0..n

1..1

isInChargeOf

0..n

isManagedBy

1..1


Association link and extentAssociation link and extentLink – association instance• represents a rolename• can be a collection of references

Extent – set of association instances• in the figure, the extend of the association is five (five links)

Order 1Shipment 1

Shipment 2

Shipment 2Order 2

Link 1 with

3 references

Link 2

Link 3

Link 5

Order 1Shipment 1

Shipment 2

Shipment 3Order 2

Link 1 with

3 references

Link 4with

2 references

Link 2

Link 3

Link 5

Order 1Shipment 1

Shipment 2

Shipment 2Order 2

Link 1 with

3 references

Link 2

Link 3

Link 5

Order 1Shipment 1

Shipment 2

Shipment 3Order 2

Link 1 with

3 references

Link 4with

2 references

Link 2

Link 3

Link 5Link 5


Association classAssociation class

Assessmentmark : List(Number)totalMark : Numbergrade : Byte

StudentCourseOffering

nn nn

Parameterized type


Composition and aggregationComposition and aggregationComposition –aggregation by valueAggregation –aggregation by referenceProperties:• Transitivity• Asymmetry• Existence

dependency

Implemented by buried references or inner classes → next slides

Book

Chapter

n

is_part_of

hasn

Sectionnn

Crate

BeerBottle

nn


Implementing aggregation by buried referenceImplementing aggregation by buried reference

public class Book {

private String title;private Chapter theChapter[];private TableOfContents theTableOfContents;public Book() {//default constructor }public boolean search(String what) {return true;}

}

Chaptertext : Textfigure : Graphics

search(what : String) : booleanChapter()

Booktitle : String

search(what : String) : booleanBook()

n

TableOfContents

generate() : VoidTableOfContents()

1n

1

-theBook

-theChapter -theTableOfContents

-theBook

not different to associationby means of variable with private visibilityhowever, in Java, classes cannot have private visibility

• subset classes must have public or package visibility


Implementing aggregation by inner classesImplementing aggregation by inner classespublic class Book {

private String title;private Chapter[] ch;private TableOfContents toc;public Book(...) { ...

toc = new TableOfContents();ch = new Chapter[numberChapters];for (int i=0; i<numberChapters; i++)

ch[i] = new Chapter();}public Void displayToc(){

toc.generate();return;

}private class TableOfContents

{private Void generate() {...}

}}

TableOfContents

generate() : VoidTableOfContents()

<<inner>>

Booktitle : S tring

displayToc() : Voidsearch(what : S tring) : booleanBook()

1-toc 1

Chaptertext : Textfigure[ ] : Graphics

search(what : String) : booleanChapter(chNum : int)

<<inner>>

n-ch n

inner class can be private (accessible

only from outer class)

outer class instantiates inner objects in its own constructor


GeneralizationGeneralizationPerson

fullName : StringdateOfBirth : java.util.Date

age() : intgetYear() : intgetYear(date : java.util.Date) : intPerson()

EmployeedateHired : java.util.Datesalary : intleaveEntitlement : intleaveTaken : int

remainingLeave() : intEmployee()

public class Person{

private String fullName;private Date dateOfBirth;public Person(){...}public int age(){

return getYear() - getYear(dateOfBirth);}

}

public class Employee extends Person{

private Date dateHired;private int salary;private int leaveEntitlement;private int leaveTaken;public Employee(){...}public int remainingLeave(){

return leaveEntitlement - leaveTaken;}

}

A subclass inherits the structure and behavior of its superclass


PersonfullName : StringdateOfBirth : java.util.Date

age() : intPerson()

EmployeedateHired : java.util.Datesalary : intleaveEntitlement : intleaveTaken : int

remainingLeave() : intEmployee()

ManagerdateAppointed : java.util.DateleaveSupplement : int

remainingLeave() : intManager()

PolymorphismPolymorphism

The same signature(operation name and the number and type of arguments)

public class Manager extends Employee {

private Date dateAppointed;private int leaveSupplement;public Manager() {...}public int remainingLeave() {int mrl;mrl = super.remainingLeave() + leaveSupplement;return mrl;

}}


Multiple inheritanceMultiple inheritancePerson

fullName : StringdateOfBirth : Date

age() : Integer

Teacher S tudent

Tutor

PostgraduateStudent


Multiple classificationMultiple classificationMultiple inheritance• A class may have many

superclasses, but a single class must be defined for each object

Multiple classification• An object is

simultaneously the instance of two or more classes

The problem arises if The problem arises if PersonPerson is specialized in few orthogonal is specialized in few orthogonal hierarchies hierarchies

PersonPerson can be can be EmployeeEmployee or or StudentStudent, , MaleMale or or FemaleFemale, , ChildChild or or AdultAdult, etc. , etc.

Without multiple classificationWithout multiple classificationneed to define classes for each legal combination between need to define classes for each legal combination between the orthogonal hierarchies the orthogonal hierarchies ChildFemaleStudentChildFemaleStudent etc.etc.


Dynamic classificationDynamic classificationAn object does not only belong to multiple classes but it can gain or lose classes over its lifetimeA Person object can be just an employee one day and a manager (and employee) another dayIn most current object-oriented programming environments, an object cannot change its class after it has been instantiated (created)


Abstract classAbstract classParent class that will not have direct instance objectsAbstract class cannot instantiate objects because it has at least one abstract operation

public abstract class VideoMedium{

public abstract Double rentalCharge();}

public class VideoDisk extends VideoMedium{

public VideoDisk() {...}public Double rentalCharge() {return null;

}}

VideoMedium

rentalCharge() : Double

V ideoTape

V ideoTape()renta lCharge() : Double

VideoDisk

VideoDisk()rentalCharge() : Double


Interface Interface vsvs abstract classabstract classInterface – a definition of a semantic type with attributes (constants only) and operations but without actual declarations (implementations) of operations• classes that implement the interface provide the declarations

Abstract class has undesirable effect of the fragile base class problemUnlike abstract classes• interfaces are helpful for modeling situations that ask for multiple

inheritance• interface does not implement (even partially) any of its methods

–– but still, but still, pure abstract class pure abstract class ≠≠ interfaceinterface• in case of interface, any class in the system can implement it, not just the

subclasses• a class can implement any number of interfaces

• interface defines a reference type that separates client objects from the implementation changes in the supplier objects

–– the implementation of the interface can change and the client obthe implementation of the interface can change and the client object ject may not be affectedmay not be affected


Multiple implementation inheritance not allowed in JavaMultiple implementation inheritance not allowed in Java

VideoMedium


VideoTape

VideoTape()rentalCharge() : Double

VideoDisk


VideoPlayer

VideoEquipmentpurchasePrice : DoubledateOfPurchase : java.sql.Date

VideoCamera

Not allowed in Java!


Implementing Java interfaceImplementing Java interface

VideoMedium


VideoTape


V ideoDisk


V ideoPlayer

V ideoP layer()renta lCharge() : Double

SoundSystem


VideoCamera

public interface VideoMedium{

Double rentalCharge();}

public class VideoPlayerextends VideoEquipmentimplements VideoMedium

{public VideoPlayer() {...}public Double rentalCharge() {return null;

}}


Using interface to eliminate dependency to supplierUsing interface to eliminate dependency to supplier

VideoTape


V ideoDisk


V ideoPlayer

V ideoP layer()renta lCharge() : Double

SoundSystem


VideoCamera

ChargeCalculator

getRentalCharge() : DoubleChargeCalculator()

VideoMedium


theVideo

<<uses>>

public class ChargeCalculator{

VideoMedium theVideo;public Double getRentalCharge() {return theVideo.rentalCharge();

}}


SummarySummaryEach object has a state, behavior and identityThere are instance objects and class objectsClass defines attributes and operationsThere are three kinds of relationships –association, aggregation, generalizationGeneralization provides the basis for polymorphism and inheritanceCommercial programming environments support multiple inheritance directly (C++, C#) or by means of interfaces (Java)Multiple and dynamic classification is still not supported commerciallyAbstract classes and interfaces are important in modeling

chapter 3comp.mq.edu.au/books/rasd2ed/readersarea/lecturesli… · · 2008-12-07chapter 3.1...

Documents