Object-Oriented Software Engineering More Modelling with Classes Paul J Krause

More Modelling with Classes Contents  Overview of Associations  Generalisation/Specialisation hierarchies  Aggregation  Why I don’t like aggregation  Interfaces Some examples taken from: Mellor and Balcer, Executable UML, Addison Wesley

Class Tuner class name channel frequency attributes get_Frequency set_Frequency operations

Inheritance Hierarchy Tuner A/V TunerFM Tuner

Aggregation Surf List surfListSize addSurfChannel deleteSurfChannel setSurfChannel Source ID presetNumber presetName setPresetNumber setPresetName 0..*

Association Tuner Surf List 1 1

Putting it all together A/V Source Front EndExternal Source Surf List Source ID 0..* 1 1 Tuner 1..* is tuned to

Publisher name address webSite BookProduct bookNumber title unitPrice Customer name shippingAdd Author name address webSite R1R3 R2 is produced and marketed by produces and markets is a purchase of is sold as wrote was written by 10..*1..* 0..* 1..* Order quantity salePrice date makes1..* is made by 1

“Nonuniform Classes”  Consider an on-line “book store”. It may actually sell a variety of products. Product productID: ProductCode title: string copyright: Year unitPrice: Money description: string bookNumber: ISBN subtitle: string recordingLength: Time productVersion: string applicable to all Products only for Books only for Recordings (CDs, videos …) only for Software

Separate Product Classes? BookProduct productID: title: copyright: unitPrice: description: bookNumber: subtitle: RecordingProduct productID: title: copyright: unitPrice: description: recordingLength: SoftwareProduct productID: title: copyright: unitPrice: description: productVersion:

Partitioning Products All Products Recording Products Book Products No Products remain outside a set No products are in more than one set

Generalisation - Specialisation BookProduct bookNumber: subtitle: RecordingProduct recordingLength: SoftwareProduct productVersion: Product productID: title: copyright: unitPrice: description: R11 {disjoint, complete}

Definitions  A superclass is a class that is a generalisation of a set of concepts  A subclass is a specialisation of a high-level concept  A leaf-subclass is a subclass that is not also a superclass of another class  Generally, superclasses will be abstract classes it is not normally possible to create instances of them it is not normally possible to create instances of them

Repeated Specialisation Account {abstract} CheckingAccount {abstract} SavingsAccount RegularCheckingAccountInterestCheckingAccount R1 {disjoint, complete} R2 {disjoint, complete}

Adding an Association Publisher groupCode: publisherCode: name: address: website: is produced and marketed by produces and markets 1 0..* R1 BookProduct bookNumber: subtitle: RecordingProduct recordingLength: SoftwareProduct productVersion: Product productID: title: copyright: unitPrice: description: R11 {disjoint, complete}

Aggregation - “part of” Vehicle TransmissionEngineWheels “A Vehicle is an aggregation (made up) of an Engine, a Transmission and some Wheels (and some more stuff… )”

Complex structures? Picture Sound Features Installation Features Timer Parental Control Child Lock Sleep Parental Control Block All Clear TV Rating Film Rating TV Rating TV Y TV Y7 PG TV 14 …

Menu MenuItem 1..* LeafItemSubMenu 1 is selected from selects 1

Avoiding Aggregation Vehicle Engine powers is powered by 1 1..* Transmission Wheel transmits power through is driven by 1 10,1 1..* generates motion via is rotated by is supported by 1..* 1 supports

Aggregation - Who needs it? Menu MenuItem 1..* LeafItemSubMenu 1 is selected from selects 1 1 consists of is contained in

Interfaces  Sometimes we may find two or more different subclasses share some common behaviour  In this case, they are not strictly “kinds of” some common parent  Rather, they “behave like” some common pattern (under certain circumstances)  We say that they both implement a common interface

A “Cashier” Interface PersonMachine ATMEmployee «interface» Cashier withdraw deposit