Date post: | 22-Dec-2015 |
Category: |
Documents |
View: | 236 times |
Download: | 5 times |
1
Chapter 22Chapter 22Object-Oriented Object-Oriented
DesignDesign
2
Object-Oriented Object-Oriented DesignDesign
responsibilitiesdesign
messagedesign
class and objectdesign
subsystemdesign
3
OOA and OOA and OODOOD
Object-relationship
model
Object-BehaviorModel
CRCIndex Cards
Attributes, operations,collaborators
THE ANALYSIS MODEL
responsibilitiesdesign
messagedesign
Class and objectdesign
subsystemdesign
THE DESIGN MODEL
Use cases
4
OOA and OOA and OODOOD
classesclassesattributesattributesmethodsmethodsrelationshipsrelationshipsbehaviorbehavior
Analysis ModelAnalysis Model
objectsobjectsdata structuresdata structuresalgorithmsalgorithmsmessagingmessagingcontrolcontrol
Design ModelDesign Model
5
Design Design IssuesIssues decomposability—the facility with which a design decomposability—the facility with which a design
method helps the designer to decompose a large method helps the designer to decompose a large problem into subproblems that are easier to solve;problem into subproblems that are easier to solve;
composability—the degree to which a design method composability—the degree to which a design method ensures that program components (modules), once ensures that program components (modules), once designed and built, can be reused to create other designed and built, can be reused to create other systems;systems;
understandability—the ease with which a program understandability—the ease with which a program component can be understood without reference to component can be understood without reference to other information or other modules;other information or other modules;
continuity—the ability to make small changes in a continuity—the ability to make small changes in a program and have these changes manifest themselves program and have these changes manifest themselves with corresponding changes in just one or a very few with corresponding changes in just one or a very few modules;modules;
protection—a architectural characteristic that will protection—a architectural characteristic that will reduce the propagation of side affects if an error does reduce the propagation of side affects if an error does occur in a given module.occur in a given module.
6
Generic Components for Generic Components for OODOOD
Problem domain component—the subsystems that Problem domain component—the subsystems that are responsible for implementing customer are responsible for implementing customer requirements directly;requirements directly;
Human interaction component —the subsystems Human interaction component —the subsystems that implement the user interface (this included that implement the user interface (this included reusable GUI subsystems);reusable GUI subsystems);
Task Management Component—the subsystems Task Management Component—the subsystems that are responsible for controlling and that are responsible for controlling and coordinating concurrent tasks that may be coordinating concurrent tasks that may be packaged within a subsystem or among different packaged within a subsystem or among different subsystems;subsystems;
Data management component—the subsystem that Data management component—the subsystem that is responsible for the storage and retrieval of is responsible for the storage and retrieval of objects.objects.
7
Process Flow for Process Flow for OODOOD
8
System Design System Design ProcessProcess• • Partition the analysis model into subsystems.Partition the analysis model into subsystems.
• • Identify concurrency that is dictated by the problem.Identify concurrency that is dictated by the problem.
• • Allocate subsystems to processors and tasks.Allocate subsystems to processors and tasks.
• • Develop a design for the user interface.Develop a design for the user interface.
• • Choose a basic strategy for implementing data Choose a basic strategy for implementing data management.management.
• • Identify global resources and the control Identify global resources and the control mechanisms required to access them.mechanisms required to access them.
• • Design an appropriate control mechanism for the Design an appropriate control mechanism for the system, including task management.system, including task management.
• • Consider how boundary conditions should be Consider how boundary conditions should be handled.handled.
• • Review and consider trade-offs.Review and consider trade-offs.
9
System System DesignDesign
requestclientsubsystem
contract
contract contract
request
request
serversubsystem
peersubsystem
peersubsystem
10
Subsystem Subsystem ExampleExample
assign to zonetest status
request for alarm notificationperiodic check-inrequire for configuration update
request for statusControlpanel
subsystem
Sensorsubsystem
Centralcommunication
subsystem
request for system statusspecification of type of alarm
periodic status check
11
Subsystem Design Subsystem Design CriteriaCriteria• The subsystem should have a well-defined
interface through which all communication with the rest of the system occurs.
• With the exception of a small number of “communication classes,” the classes within a subsystem should collaborate only with other classes within the subsystem.
• The number of subsystems should be kept small.
• A subsystem can be partitioned internally to help reduce complexity.
12
Subsystem Collaboration Subsystem Collaboration TableTable
13
Object Object DesignDesign A A protocol descriptionprotocol description establishes the establishes the
interface of an object by defining each interface of an object by defining each message that the object can receive and the message that the object can receive and the related operation that the object performs related operation that the object performs
An An implementation descriptionimplementation description shows shows implementation details for each operation implementation details for each operation implied by a message that is passed to an implied by a message that is passed to an object. object.
information about the object's private partinformation about the object's private part internal details about the data structures that describe internal details about the data structures that describe
the object’s attributesthe object’s attributes procedural details that describe operationsprocedural details that describe operations
14
Design Design PatternsPatterns
... you’ll find recurring patterns of classes and communicating objects in many object-oriented systems. These patterns solve specific design problems and make object-oriented design more flexible, elegant, and ultimately reusable. They help designers reuse successful designs by basing new designs on prior experience. A designer who is familiar with such patterns can apply them immediately to design problems without having to rediscover them.
Gamma and his colleagues [GAM95]
15
Design Pattern Design Pattern AttributesAttributes
The design pattern name is an abstraction that The design pattern name is an abstraction that conveys significant meaning about it applicability conveys significant meaning about it applicability and intent. and intent.
The problem description indicates the environment The problem description indicates the environment and conditions that must exist to make the design and conditions that must exist to make the design pattern applicable. pattern applicable.
The pattern characteristics indicate the attributes The pattern characteristics indicate the attributes of the design that may be adjusted to enable the of the design that may be adjusted to enable the pattern to accommodate into a variety of pattern to accommodate into a variety of problems. problems.
The consequences associated with the use of a The consequences associated with the use of a design pattern provide an indication of the design pattern provide an indication of the ramifications of design decisions.ramifications of design decisions.
16
ExExamampleple Miter joint – Dovetail joint in windowMiter joint – Dovetail joint in window
Miter Miter Simpler lightweight inconspicuousSimpler lightweight inconspicuous
Dovetail Dovetail More complex, impervious temperature and humidityMore complex, impervious temperature and humidity Independent of fastening systemIndependent of fastening system Beautiful when made wellBeautiful when made well
17
FacFacadade e
PatPatterternn
Name - FacadeName - Facade ProblemProblem
You need to use only a subset of a complex system. You need to use only a subset of a complex system. Or you need to interact with the system in a Or you need to interact with the system in a particular way.particular way.
SolutionSolution Define a new class (or classes) That has the required Define a new class (or classes) That has the required
interfaceinterface Have this new class use the existing system.Have this new class use the existing system.
18
FaçFaçadade e
(co(cont.)nt.)
Trade-offsTrade-offs The facade simplifies the use of the required The facade simplifies the use of the required
subsystem. However, since the facade is not subsystem. However, since the facade is not complete, certain functionality may be unavailable to complete, certain functionality may be unavailable to the clientthe client
19
FaFacacadedeSubsystem
Facade
20
SuSummmamary – ry –
Applies whenApplies when You do not need to use all the functionality of a complex You do not need to use all the functionality of a complex
systemsystem You want to encapsulate or hide the original systemYou want to encapsulate or hide the original system You want to use the functionality of the original system You want to use the functionality of the original system
and want to add some new functionality as welland want to add some new functionality as well The cost of writing this new class is less than the cost of The cost of writing this new class is less than the cost of
everybody learning how to use the original system or is everybody learning how to use the original system or is less than you would spend on maintenance in the futureless than you would spend on maintenance in the future
21
AdAdaptapterer Name – Adaptor (wrapper)Name – Adaptor (wrapper)
ProblemProblem A system has the right data and behavior but the A system has the right data and behavior but the
wrong interface. Often used when you have to make wrong interface. Often used when you have to make something a derivative of an abstract class we are something a derivative of an abstract class we are defining or already havedefining or already have
22
SolSolutiutionon Provide a wrapper with the desired Provide a wrapper with the desired
interfaceinterface Object adapter – Object adapter –
Adapter contains the adaptee (pointer?)Adapter contains the adaptee (pointer?) Use inline functions to forwardUse inline functions to forward
Class adapterClass adapter Use multiple inheritance – privateUse multiple inheritance – private
23
AdAdapaptortor
Client Target
Adaptor
Adaptee
24
TraTrade de offsoffs Efficiency issuesEfficiency issues
Writing function forwardingWriting function forwarding NoteNote
Facade often hides several classes but may be 1Facade often hides several classes but may be 1 Adapter often hides 1 but may be severalAdapter often hides 1 but may be several
25
FinFind d
whwhat at varvaries ies anand d
encencapsapsulaulate te itit
Abstract classAbstract class Core – defines Core – defines commonalitycommonality
Commonality Commonality Which abstract Which abstract classes to useclasses to use
VariationsVariations Derivations of Derivations of abstract classesabstract classes
SpecificationSpecification Interface of classesInterface of classes
26
AbsAbstratract ct claclass ss
Core concept - commonalityCore concept - commonality Variations are derivation of an abstract Variations are derivation of an abstract
classclass
27
SpSpecifecificaticationion, ,
IntInterferfaceace
, , ImImpleplemementantatiotionn
Specification – conceptual, identifies Specification – conceptual, identifies interfaceinterface
Specification implementation - given Specification implementation - given specification how can I implement this specification how can I implement this particular variationparticular variation
28
BriBridgdge e
PatPatterternn
Name - bridgeName - bridge Problem the derivations of an abstract Problem the derivations of an abstract
class must use multiple implementations class must use multiple implementations without causing an explosion in the without causing an explosion in the number of classesnumber of classes
29
SolSolutiutionon Define an interface for all implementations Define an interface for all implementations
to use and have the derivations of the to use and have the derivations of the abstract class use that.abstract class use that.
30
BriBridgdge e
PaPattetternrn
Abstraction Implementor
Refined Abstraction Concrete
Implementor A
Concrete
Implementor B
31
TraTradedeoffs offs The decoupling of the implementation The decoupling of the implementation
from the objects that use them increases from the objects that use them increases extensibility. extensibility.
Client objects are not aware of Client objects are not aware of implementation issues.implementation issues.
Variations of shape are encapsulated in Variations of shape are encapsulated in shape classshape class
Variations in drawing are encapsulated in Variations in drawing are encapsulated in drawing classdrawing class
32
AbsAbstratract ct
FacFactortoryy
Name: Abstract FactoryName: Abstract Factory Problem: Families of related objects need to be Problem: Families of related objects need to be
instantiated.instantiated. Solution: The abstract factory defines the interface Solution: The abstract factory defines the interface
for how to create each member of the family. Each for how to create each member of the family. Each family is created by having its own unique concrete family is created by having its own unique concrete factory.factory.
33
TraTradedeoffsoffs Isolates concrete classesIsolates concrete classes
Makes exchanging product families easyMakes exchanging product families easy Promotes consistency among productsPromotes consistency among products Hard to add new kinds of products Hard to add new kinds of products
34
AbAbstrstract act FaFactoctoryry
Client
Abstract Product A
Abstract Product B
Abstract
Factory
A1 A2 B1 B2
35
SuSummmamaryry
First, identify the rules for instantiation and define First, identify the rules for instantiation and define an abstract class with an interface that has a an abstract class with an interface that has a method for each object that needs to be method for each object that needs to be instantiatedinstantiated
Implement concrete classes from this class for each Implement concrete classes from this class for each familyfamily
The client object uses this factory object to create The client object uses this factory object to create the server objects that it needsthe server objects that it needs