© m.e. fayad 2000 -- 2006 sjsu -- cmpe software systems engineering dr. m.e. fayad, professor...

© M.E. Fayad 2000 -- 2006 SJSU -- CmpE

Software Systems Engineering

Dr. M.E. Fayad, Professor

Computer Engineering Department, Room #283I

College of Engineering

San José State University

One Washington Square

San José, CA 95192-0180

http://www.engr.sjsu.edu/~fayad

© M.E. Fayad 2000 -- 2006 SJSU – CmpE M.E. Fayad L3-5a-S2 Objects & Classes

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Lesson 14:Objects & Classes


Lesson Objectives

Objectives

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Overview of Previous Lecture

Explore Modeling Notation Understand Objects, Attributes, Operations, and Notes in UML

Discuss the following:

– Different Kind of Classes

– Class Diagrams


Notation

Notation Again !

Modeling Notation

4


Real-world systems can be decomposed into discrete

entities called objects

Objects represent things, concepts, or abstraction with

definable boundaries and behaviors

An object is specific instance of a class to which it

belongs

Classes have attributes and behaviors

Individual objects have their own specific values for each

attribute and share the same behaviors

Objects & Classes (1)

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Example Objects Classes Attributes

A computer screen Screen Resolution, # of colorsA window Window Size, location

IBM Company Name, location, total revenue

Joe Harris Employee Name, department, salary


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Objects with the same attributes, behaviors, and relationships

are grouped together into classes

A class describes general attributes and behaviors for a group of

objects

An object is a single instance of its class (e.g., IBM is an

instance of the Company class)

A Class diagram is used to describe the attributes and behaviors

of a class

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Classes (1)

Classes are the most important building block of any Classes are the most important building block of any

object-oriented systemobject-oriented system

A class is a description of a set of objects that share A class is a description of a set of objects that share

the same attributes, operations, relationships, and the same attributes, operations, relationships, and

semantics.semantics.

Graphically, a class is rendered as a rectangleGraphically, a class is rendered as a rectangle

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Classes (2)

9

RegistrationForm

RegistrationManager

Course

Student

CourseOfferingProfessor

ScheduleAlgorithm


Naming & AttributesNaming & Attributes NamingNaming

Classes should be named using the vocabulary of the domainClasses should be named using the vocabulary of the domain

Naming standards should be created -- e.g., all classes are Naming standards should be created -- e.g., all classes are

singular nouns starting with a capital lettersingular nouns starting with a capital letter

AttributesAttributes

An attribute is a named property of a class that describes a An attribute is a named property of a class that describes a

range of values that instances of the property may holdrange of values that instances of the property may hold

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Attributes

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Each course offeringhas a number, location and time

CourseOffering

numberlocationtime


OperationsOperations

An operation is the implementation of a service that An operation is the implementation of a service that

can be requested from any object of the class to affect can be requested from any object of the class to affect

behaviorbehavior

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RegistrationManager

addCourse(Student,Course)


ResponsibilityResponsibility

A responsibility is a contract or an obligation of a classA responsibility is a contract or an obligation of a class

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RegistrationManager

Responsibility:-- manage the registration

process


Finding Classes

Where to find candidate classes:Where to find candidate classes:

o Nouns in descriptions or conversationNouns in descriptions or conversation

o Checklists of general/typical object typesChecklists of general/typical object types

o Similar computerized systemsSimilar computerized systems

o Technical literature in the problem domainTechnical literature in the problem domain

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Example Classes

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Phenomena Classes

Thing Car, goods, packaging, materials

People & roles Employee, parent, customer, member

Organizations Company, department, group, project

Places Shelf, parking spot, construction site, city

Concepts Square, currency, quality parameters, fee

Resources Money, time, energy, labor force, info

Apparatuses Radar, sensor, valve, motor

Systems Street register, cash register, alarm system


Evaluating Classes

Does the class contain unique information?Does the class contain unique information?

Does the class encompass multiple objects?Does the class encompass multiple objects?

Can we identify objects from the class?Can we identify objects from the class?

Does the class have a manageable number of Does the class have a manageable number of

operations?operations?

Does the class embodies a well-defined responsibility?Does the class embodies a well-defined responsibility?

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Classes in UML (1)

Class AbstractClass

<<utility>>UtilityClass

attribute

operation()

<<Stereotype>>Package::Class{Constraints}

Syntax for attributes and operationsAttribute[Cardinality]:Package::Type = InitialValue {Constraints}Operation(ArgumentList):ReturnType {Constraints}

<<metaclass>>MetaClass

<<ActiveClass>>ActiveClass


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Classes in UML (2)

ParameterizedClass

ParameterizedClass<Parameter>

i:Element

normalOperation()abstractOperation()/derivedOperation()

classOperation()publicOperation()

#protectedOperation()-privateOperation()

Class

normalAttribute/derivedAttribute

classAttributepublicAttribute

#protectedAttribute-privateAttribute

Class


Related Terms: Type

Definition: Class = Attributes + Operations

A class includes the definition of potential constraints, tagged values, and stereotypes.

Notation:

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Classes in UML (3)

Class

attribute1attribute2

operation1()operation2()

Class


Class


Class

Class



Class


<< .. >> stereotype

{ .. } tagged values

:: separate package and class names

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Classes in UML (4)

attribute: Type=InitialValue {Constraints}

operation(Paramter) {Constraints}

<<Stereotype>>Package::Class

{PropertyValues}


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Classes in UML (5)

Circle

Class name

Attribute names

Attribute type

Operations

Class Example

Constraint

Initial value

Parameters(name: type = initial value)

radius {radius>0}centerpoint: Point = (10, 10)

display(0remove()

setPosition(pos: Point)setRadius(newRadius)

Graphics::Circle

Package name


In Smalltalk and CLOS, classes are simply objects, that is, classes can be sent messages, and they can include (class) attributes.

In C++, class attributes and operations can be emulated by declaring them as static.

However, in C++ classes cannot be treated like objects. An example for a class message or a class operation is new, which is used to create a new instance of a class.

In Smalltalk for example:

newObject := Class new;

anEmployee := Employee new;

Classes of class objects are called metaclasses and similarly to a normal class, noted with a stereotype <<metaclass>>

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Classes in UML (6) - Metaclasses

<<metaclass>>CustomerClass


In UML, metaclass is a class describing itself or other classes.

In UML, class operations need not be noted within the metaclass; they may also be contained in the class itself, where they are underlined in order to distinguish them from normal operations.

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Classes in UML (7) - Metaclasses

numInstance: Integername: String

birthDate: Date

new(name)age(): Integer

Person

numInstance: Integer

new(name)

<<metaclass>>PersonClass

<<instance of>>


Definition:

A parameterized class is a template equipped with generic formal parameters, which can be used to generate common (non-parameterized) classes.

The generic parameters serve as placeholders for the actual parameters which represent classes or simple data types.

Description:

In a parameterized class, no concrete class is defined, but only a template for generation of classes.

These templates are usually a type of macro technique which has no special function, apart from a text replacement.

In statically typed languages, parameterized classes are an important means for writing re-usable code.

C++ and Eiffel support parameterized classes. 24

Classes in UML (8) - Parameterized Classes


A class generated with the aid of a parameterized class is called a bound element.

Notation

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Classes in UML (9) - Parameterized Classes

i:Element

WaitingQueue

add()remove()

TrafficJam

WaitingRoom

<<bind>> (Car)

<<bind>> (Patient)

WaitingQueue<Car>


Related Terms: virtual class

Definition:

– An Abstract class is never used to generate object instances.

– It is intentionally incomplete and thus forms the basis for further subclasses which can have instances.

Description:

Abstract classes often represent a general term, a generic term for a set of concrete terms.

Thus a vehicle can be an abstract generic term for bicycle, car, truck, train, and airplane.

Vehicle in this case is merely an abstraction, a generalization.26

Classes in UML (9) - Abstract Classes


An abstract class is always a superclass.

An abstract class that has no subclasses makes no sense. Either it is superfluous, or it lacks a concrete class as subclass.

Notation

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Class{abstract}

attributes

Operations()

Class

attributes

Operations()

Class

Class{abstract}


Example

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GeomFigure

Triangle Circle Rectangle

Abstract Class

Concrete Class


Utility classes are collections of global variables and functions which are combined into a class.

The stereotype <<utility>> marks a class as a utility class

Utility classes are not true classes, but collection of global variables and functions which are, however, noted in the form of a class.

In OO, they are usually not needed.

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Classes in UML (9) - Utility Classes

sin(angle): Realcos(angle): Realtan(angle): Realcot(angle): Real

<<utility>>MathFun


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Objects in UML (1)

Object : Class

attributeName = value

Object

:Class

ActiveObject

Multiobject


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Objects in UML (2)

Related terms: instance Definition:

– An object is a unit which actually exists and acts in the current system.

– Each object is an instance of a class.

– An object contains information represented by the attributes whose structure is defined in the class.

– An object can receive the messages defined in the class, that is, it has appropriate operations for each message defined.


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Objects in UML (3)

Description:

– An alternative term for object is instance.

– A class contains the definition of objects, that is, their abstract description.

– The behavior of an object is described through the possible messages it can understand.

– For each message, the object needs appropriate operations.


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Objects in UML (4)

Notation– Objects are represented by rectangles which either

bear only their own name, or which in addition show the name of their class, or the values of specific or all attributes.

– If attribute values are indicated, the rectangle is divided into two sections, separated by a horizontal line.

– The name of the object is underlined, and usually begins with a lower case letter.


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Objects in UML (5)

Example:

aCircle: Circle

Radius = 25Center = (10,10)

Instance name

Attribute names

Class name

Attribute values


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Attributes in UML (1)

Related terms: data element, instance variable, variable, member

Definition:– An attribute is a (data) element which is

contained in the same way in each object of a class and is represented by each object with an individual value.


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Description: Each attribute is at least described by its name. In addition, a

data type or a class, plus an initial value and constraints may be defined.

Constraints can be used in addition to the type specification to further restrict the value range or value set of the attribute, or to make it dependent on other conditions.

Tagged values can be used to specify additional special properties. Thus, for example, the tagged value {readonly} indicates that an attribute may only be read.


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Notation:– Attribute names begin with lower-case characters and class

names with upper-case one, while tagged values and constraints are enclosed in braces

• attribute : Package::Class =

InitialValue {PropertyValue} {Constrant}

– Derived attributes are marked by a prefixed slash (/)

/derivedAttribute

classAttribute

+publicAttribute

#protectedAttribute

-privateAttribute


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Examples:

name: String = ‘Unknown’

invoiceDate : Date = today

birthDate : Date

color : {red, blue, green}

radius : Integer = 25 {readonly} {radius>0}

/numChildren {numChildren = childrenSet count}

/age {age = today - birthDate}

-counter : Integer

dynamicArray[*]


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Operations, Methods in UML (1)

Related terms: method, service procedure, routine function, message

Definitions:– Operations are services which may be required from an object.

– They are described by their signature (operation name, parameters, and if needed, return type).

– A method implements an operation; it is a sequence of instructions.

– A message passes an object the information on the activity it is expected to carry out, thus requesting it to perform an operation.


Description– A message consists of a selector (a name) and a

list of arguments, and is directed to exactly one receiver.

– The sender of a message is as a rule returned exactly one response object.

– Inside a class definition, an operation has a unique signature composed of the name of the operation, potential parameters, and a potential return value (function result).

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Description (continued)– Operations may be provided with constraints which

can describe the conditions to be met at the call or the values the arguments may have, among other things.

– Tagged values can be used to describe additional special features. Some tagged values are:

• {abstract} to indicate an abstract operation

• {obsolete} to indicate that this operation exists only for compatibility with previous versions.

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Notation– The signature of an operation is given as

follows:• name(argument : ArgumentType = DefaultValue, …):

ReturnType {PropertyValues} {Constraints}

– Example:• setPosition(x : Integer = 1, y : Integer =1):

Boolean {abstract} {(x > 0) and (y > 0)}

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Naming Conventions– Be extremely careful with the naming of

operations. You should be conscious of what the operation is supposed to do and for which outcomes it is responsible.

– Always try to use active verbs, be careful with adjectives, and be precise!

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Related terms: usage context, constraint Definition:

– Stereotypes are project-, enterprise-, or method-specific extensions of pre-existing model elements of the UML metamodel. According to the semantics defined with the extension, the model element to which the stereotype is applied are semantically directly affected.

– In practice, stereotypes mainly specify possible usage contexts of a class, a relationship, or a package.

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Stereotypes in UML (1)


Description:– A stereotype is UML’s way of attaching extra

classifications to model items; it is one of the ways that UML is made extensible. The stereotype describes a model element, and is placed close to the affected element on a diagram, giving extra information about that element

– Some stereotypes are predefined in UML; they are automatically available and cannot be redefined. <<interface>>, <<type>>, and <<implementation class>> are examples. 45



Description: (continued)– Stereotypes can be defied to express

whatever extra classification may be deemed useful.

– For example, if an application had persistent classes, the stereotype <<persistent>> could be defined to show which classes are persistent.

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Notation:– The stereotype is placed before or above the

element name and enclosed in French quotes (<<>>)

– Alternatively, special symbols may be used (decorative stereotypes). These can be seen in Rational Rose. Some of the elements that are represented in this manner are: <<actor>>, <<control>>, <<entity>>, and <<boundary>>. 47



Examples:– Stereotypes can, for example, be used to

indicate the meaning of a class in the application architecture, such as:

• <<presentation>>, <<process>>, <<domain class>>.

– Further examples:• <<model>>, <<view>>, <<controller>>,

<<exception>>, <<primitive>>, <<enumeration>>, <<signal>>, <<complete>>, <<incomplete>>, <<implements>>, <<uses>>, <<extends>>

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Definition:– Interfaces describe a selected part of the

externally visible behavior of model elements (mostly of classes and components).

– Interface classes are abstract classes which define abstract operations, exclusively.

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Interfaces & Interface Classes in UML (1)


Description:– Interfaces are specifications of the external behavior of

classes and contain a set of signatures for operations that classes wishing to provide this interface need to implement.

– Operations in an interface need not be explicitly marked as {abstract}, because this is mandatory.

– Common classes that wish to implement an interface need to provide all the operations defined in the corresponding interface class.

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Notation:– Interface classes are noted in the same way as

common classes, except that they bear the stereotype <<interface>>.

– They do not need a compartment for attributes, as they contain only operations.

– Operations in interface classes define only signatures; they are abstract and should therefore be set in italics. 51



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Example:

String

isEqual(String):BooleanisGreater(String):Boolean

Length():Integer

<<interface>>Sortable

isEqual(Object):BooleanisGreater(Object):Boolean

Realization Relationship


Related terms: restriction, integrity rule, condition, tagged value, stereotype, not dependency, invariant, assertion.

Definition:– A constraint is an expression which restricts the

possible contents, states or the semantics of a model element and which must always be satisfied.

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Constraints in UML (1)


Description:– A constraint describes a condition or integrity

rule.

Notation:– Constraints are enclosed in braces:

• { Constraint }

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Constraints in UML (2)


Dependency

55

Constraints’ Examples in UML (3)

Project Employee{subset} 11..*

has

consists of

projectLeader

projectMembers

Project Employee11..*

has

consists of

projectLeader

projectMembers

Project self.projectMembers -> includes (self.projectLeader)


Consistency

56


Customer

Contract

1

0..*

has

receives

based on

Invoice self.contract.customer = self.customer

Invoice

1

1

0..*


OR

57


Person

Domesticaddress

{or}

*

*

has

Foreignaddress

has


Values

58


Rectangle

a {a > 0}b {b > 0}

Triangle

a {c-b < a < b+c}b {a-c < b < a+c}c {a-b < c < a+b}


Order

59


NameList1..*contains

{ordered: lastName}

1 Person

lastNamefirstName


Formulas

60


Person

birthDate : Date/age {age = today - birthDate}

{/age = today - birthDate}

Person

birthDate : Date/age


Enumerations

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ShoppingSpree1..*

paricipants

{participant.age > 65}1 Person

age


Related terms: property string, feature, characteristic, constraint.

Definition:– Tagged values are user-defined, language and

tool specific keyword/value pairs which extend the semantics of individual model elements with specific characteristic properties.

62

Tagged Values in UML (1)


Description:– Tagged values add specific additional properties

to existing model elements. They detail the semantics of a model element and can influence code generation.

Notation:– Tagged values consist of a keyword and a

value, and are enclosed in braces.

63



64


Examples:– {abstract}– {readonly}– {private}– {obsolete}– {version=2.1}

GeomFigure{abstract Version=1.3}

visible : Boolean {readonly}

display() {abstract}remove() {abstract}getPosition(): PointsetPosition(p: Point)

setPos(x,y) {obsolete}


Related terms: category, subsystem Definition:

– Packages are collections of model elements of arbitrary types which are used to structure the entire model into smaller clearly visible units.

– A package defines a namespace, that is , the names of the elements within a package must be unique.

– Each model element can be referenced in other packages, but it belongs to exactly a single (home) package.

– The package can in turn contain packages. The top package includes the entire system.

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Packages in UML (1)


Description:– Packages my contain different model elements,

for example, classes and use cases. They may be hierarchically structured, with packages inside packages.

– Packages are built on the basis of logical or physical relationships.

66

Packages in UML (2)


Description:– A model element can be contained in several

packages, but each element has its home package. In all other packages, it can only be quoted in the form:

• PackageName::ClassName

– This creates dependencies between the packages: one package uses classes of another package. 67

Packages in UML (3)


Description:– A good architecture leads to few

dependencies between packages. – Packages are also suitable working entities

for project management and organization.

68

Packages in UML (4)


Notation – A package is represented as a folder. Inside this symbol,

the name of the package is noted. – The dependencies between packages are noted by a

dashed arrow which points toward the independent package.

– It is also possible to represent generalization relations between packages if the model elements contained in the packages are generalizations or specializations of elements contained in other packages.

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Packages in UML (5)


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Packages in UML (6)

ExampleProductProduct

Online Tariffing

Online Tariffing

Tariffing Life

Tariffing Life

LifeLife

Contents&PL

Contents&PL

PartnerPartnerTariffing Contents

Tariffing Contents


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Notes in UML (1)

Related Terms: annotation, comment

Definition: Notes are comments to a diagram or an arbitrary element in a diagram, without any semantic effect.

Description: notes are annotations to classes, attributes, operations, relationships, and the like.

Some analysis and design tools provide the possibility of creating notes with user-defined structures and names


72

Notes in UML (2)

Note Notation & Example:

Invoice

invPositions : Set

sumPositions()sumVAT()

InvPosition

quantityitem

unitPrice

totalPrice()

*1

sumPositions “This example is in Smalltalk” “Return total amount of all invoice positions” | s | s:= 0. invPositions do: [:p | s:= s + ( p totalAmount).]. ^s.


Related items: mechanism

Description: Class models and the like are substantially easier to understand when one knows where design patterns have been employed.

Therefore, it is sensible to document this in the model in an appropriate manner. 73

Cooperation / Design Pattern Notation in UML (1)


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Cooperation / Design Pattern Notation in UML (2)

Productelement

ProductProduct

price

Contract11..*

composite

Composite(Gamma et al. 1995)

sheet

componentclient


• T/F statements

1. Abstract classes are used to generate object instances

2. Legacy Software is any preexisting software that must be replaced by, incorporated into, or interfaced with software that is currently being developed

3. Utility class contains global variables and functions.

4. Design patterns identify, name, and describe common and recurring designs appearing frequently in object-oriented systems.

• Define in UML: Abstract Classes, Objects, Metaclasses, Parameterized Classes, Utility Classes, and Notes

75

Discussion Questions


76

Questions for the Next Lecture

Define:–RRelationships–AAssociation relationships

Aggregation

Inheritance

–A

© m.e. fayad 2000 -- 2006 sjsu -- cmpe software systems engineering dr. m.e. fayad, professor...

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