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Object-Oriented Analysis and DesignCHAPTERS 16: UML CLASS DIAGRAMS

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What will we learn?UML Class Diagrams – What are they, how to create them

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IntroductionUML provides the tools for creating general class diagrams, i.e. static object modeling, that can be used to create Domain Models or software class diagrams

We will look in more detail at the UML notation that can be used, irrespective of the perspective (conceptual or software class)

Note that UML provides a set of diagraming tools, most of which are optional to useStandardized diagram language, makes it easier to communicate designs

The next slide gives an overview of the concepts we will be discussing in this lecture

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java.awt::Fontor

java.awt.Font

plain : Int = 0 { readOnly }bold : Int = 1 { readOnly }name : Stringstyle : Int = 0...

getFont(name : String) : FontgetName() : String...

«interface»Runnable

run()

- ellipsis “…” means there may be elements, but not shown- a blank compartment officially means “unknown” but as a convention will be used to mean “no members”

SubclassFoo

...

run()...

SuperclassFooor

SuperClassFoo { abstract }

- classOrStaticAttribute : Int+ publicAttribute : String- privateAttributeassumedPrivateAttributeisInitializedAttribute : Bool = trueaCollection : VeggieBurger [ * ]attributeMayLegallyBeNull : String [0..1] finalConstantAttribute : Int = 5 { readOnly }/derivedAttribute

+ classOrStaticMethod()+ publicMethod()assumedPublicMethod()- privateMethod()# protectedMethod()~ packageVisibleMethod()«constructor» SuperclassFoo( Long )methodWithParms(parm1 : String, parm2 : Float)methodReturnsSomething() : VeggieBurgermethodThrowsException() {exception IOException}abstractMethod()abstractMethod2() { abstract } // alternatefinalMethod() { leaf } // no override in subclasssynchronizedMethod() { guarded }

3 common compartments

1. classifier name

2. attributes

3. operations

interface implementation andsubclassing

Fruit

...

...

PurchaseOrder

...

...

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association with multiplicities

dependency

officially in UML, the top format is used to distinguish the package name from the class name

unofficially, the second alternative is common

order

an interface shown with a keyword

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UML: Design Class Diagram (DCD)

Register

...

endSale()enterItem(...)makePayment(...)

Sale

timeisComplete : Boolean/total

makeLineItem(...)

Register

...

Sale

timeisComplete : Boolean/total

Captures

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11Domain Model

conceptual perspective

Design Model

DCD; software perspective

currentSale

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Classifiers, AttributesA UML classifier is a model element that describes behavioral and structure features

Think of classes or interfaces

Attributes may also be called structural properties

Attributes may be displayed in several ways in a UML diagram:Text in a class boxOn an association lineBoth of the above

Full format for attribute text notation (note most items are optional):

Visibility name : type multiplicity = default {property-string}

Note that Visibility is the +- notation we saw earlier (+ public, - private)

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UML: Notating Attributes

Register

...

...

Sale

...

...

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Register

currentSale : Sale

...

Sale

...

...

using the attribute text notation to indicate Register has a reference to one Sale instance

using the association notation to indicate Register has a reference to one Sale instance

OBSERVE: this style visually emphasizes the connection between these classes

currentSale

Register

currentSale : Sale

...

Sale

...

...

1thorough and unambiguous, but some people dislike the possible redundancy

currentSale

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Attributes As AssociationsNotice that there are subtle differences between the conceptual perspective (Domain Model) and software perspective (Design Model) for attributes that are defined as associations

For DCDs, there is usually A navigability arrow A multiplicity at the target end, but not the sourceA role nameNo association name

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UML: Attributes as Associationsthe association name, common when drawing a domain model, is often excluded (though still legal) when using class diagrams for a software perspective in a DCD

Register

id: Int

...

Sale

time: DateTime

...

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currentSale

Register

id : Int

Sale

time : DateTime

Captures-current-sale1 1UP Domain Modelconceptual perspective

UP Design ModelDCD

software perspective

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Attributes: Text versus Associations

We explored the idea of data type objects earlier (Domain Models)Data types referred to objects for which individual identity is not importantRecall a Person object versus a Name data type

One guideline is to use the text for data types (basically primitive types) and associations for more complicated classes

Note that this is a diagram preference – does not matter in the final code

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UML: Attributes as Associations

Register

id: Int

...

Sale

time: DateTime

...

1applying the guideline to show attributes as attribute text versus as association lines

Store

address: Addressphone: PhoneNumber

...

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Register has THREE attributes:1. id2. currentSale3. location

currentSale

location

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Attributes: ListsHow do we notate a list of attributes, e.g. an ArrayList in Java?

notice that an association end can optionally also have a property string such as {ordered, List}

Sale

time: DateTime

...

SalesLineItem

...

...

1..*lineItems

{ordered, List}

Sale

time: DateTimelineItems : SalesLineItem [1..*] orlineItems : SalesLineItem [1..*] {ordered}

...

SalesLineItem

...

...

Two ways to show a collection attribute

“Note” Symbol

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Operations and MethodsOperations are usually displayed in the class box with the notation:

visibility name (parameter-list) {property-string}

Sometime a return-type is value is added

Assume public if no visibility is shown

An operation is a declaration (name, parameters, return type, exceptions list)

A method is an implementation of an operation in sequence diagrams, may show the details and sequence of messages In class diagram, usually include some pseudo-code in a note with the <<method>> tag

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Method Notation in UMLRegister

...

endSale()enterItem(id, qty)makeNewSale()makePayment(cashTendered)

«method»// pseudo-code or a specific language is OKpublic void enterItem( id, qty ){ ProductDescription desc = catalog.getProductDescription(id); sale.makeLineItem(desc, qty);}

Often times constructors (if included) are notated with the <<constructor>> tag

Usually, getters and setters are ignored in class diagrams They are assumed to exist, or are added to the code on an as-needed basis

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KeywordsKeywords are textual adornments used to categorize a model element – they provide some additional information about the element.

Usually notated <<keyword>>, and sometimes {keyword}

Some examples:<<actor>> - this entity is an actor<<interface>> - this entity is an interface{abstract} – this is an abstract element, it can’t be instantiated{ordered} – this set of objects is ordered, e.g. the ArrayList example shown earlier

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Abstract Classes As we saw earlier in Domain Models, UML has the ability to denote generalization

Solid line with open, fat arrow; can also notate {abstract} in super-classIt represents a relationship between more general classifier and more specific classifier. The specific classifier indirectly has the features of the more general classifier

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Dependency in UMLIn UML, dependency lines can be used in any diagram, but they are especially common in class and package diagrams.

In UML, a general dependency relationship indicates that a client element (class, package, use case, etc.) has knowledge of a supplier element and that a change in the supplier could affect the client

Indicated by a dashed arrow from the client to the supplier

Note that we often associate elements with associations (e.g. super- and sub-classes as we just saw), so we do not need to add dependency arrows if an association already exists

Often used when a class has an attribute of another class type, or if one class sends a message to another class

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Dependency in UMLGuideline: Use dependency in UML to depict global parameter variable, local variable, and static-method call to another class.

SalesLineItem

...

...

ProductDescription

...

...

1..*lineItems

Sale

...

updatePriceFor( ProductDescription )...

the Sale has parameter visibility to a ProductDescription, and thus some kind of dependency Public class Sale

{Public void updatePrice(ProductDescription description) { Money basePrice = description.getPrice(); …. } ….}

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Dependency in UML

Public class Foo{Public void doX() { system.runFinalization(); …. } ….}

System

...

runFinalization()...

Foo

...

doX()...

the doX method invokes the runFinalization static method, and thus has a dependency on the System class

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Dependency Labels

«call»Window

a dependency on calling on operations of the operations of a Clock

Clock

getTime()...

«create»A

a dependency that A objects create B objects

B

...

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«interface»Timer

getTime()

Clock1

...

getTime()... lollipop notation indicates Clock3 implements

and provides the Timer interface to clients

Timer is a provided interface

Timer

Clock3

...

getTime()...

Window2

Window3

dependency line notation

Window2 has a dependency on the Timer interface when it collaborates with a Clock2 object

socket line notation

Window3 has a dependency on the Timer interface when it collaborates with a Clock3 object

Window1 Timer

socket line notation

Window1 uses the Timer interface

it has a required interface

Clock2

...

getTime()...

Clock1 implements and provides the Timer interface

Timer

Interfaces may be notated in various ways in UML

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Composition and AggregationWe saw this earlier in Domain Models …

Composition is a whole-part relationship between model entities, such thatan instance of the part belongs to only one instance of the compositea part must belong to a compositethe composite is responsible for creating/deleting the parts. (So if the composite is destroyed, the parts are destroyed or become attached to another composite.)

Aggregation is a weaker form of composition, where the above requirements are not necessarily true

Aggregation does not imply ownership of the parts

Composition involves instantiating objects, aggregation involves pointers to other objects

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Composition: Example

Finger0..7

Hand

composition

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Square40

Board1

SalesLineItem1..*

Sale1

composition means -a part instance (Square) can only be part of one composite (Board) at a time

-the composite has sole responsibility for management of its parts, especially creation and deletion

Generally look for “has a” associations

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Constraints and Qualified Associations

In UML diagrams, a constraint is a restriction on an element

Usually indicated as some text between curly braces in the diagram, either in the class box or next to it

Associations may be qualified – this means the association may depend upon a particular key or parameter.

In the example on the next slide, we see a ProductCatalog that contains many ProductDescriptions. Each one is identified by an itemID.

Note the change in multiplicity in the UML diagram; the association is now related to a single instance, but it is understood that the there may be many associations

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Qualified Association

ProductCatalog

ProductDescription

itemID Contains

ProductCatalog

ProductDescription

Contains

1..*

multiplicity reduced to 1

(a)

(b)

qualifier

1

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Association ClassesIn UML, an association may be considered a class, with attributes, operations, and other features

Include this when the association itself has attributes associated with it

salarystartDate

Employment

EmploysCompany Person**

a person may have employment with several companies

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Takeaways from Chapter 16Understand the basics of reading UML diagrams, in particular with how they represent class diagrams.

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Next …Chapter 15 – Creating interaction diagrams in UML