f10-1: adm, architectural patterns, design patterns and ... · f10-1: adm, architectural patterns,...
Post on 07-May-2018
224 Views
Preview:
TRANSCRIPT
19.04.2010
1
ICT
INF5120 – Modellbasert
Systemutvikling
F10-1: ADM, Architectural Patterns, Design
Patterns and Refactoring
Forelesning 12.04.2010
Arne-Jørgen Berre
ICT 2
INF5120 - Lecture plan - 2010 1: 25/1: Introduction to MBSU, MDA, OO and Service/SOA modeling, Overall EA, 4 parts: MDE/SSS/MS/MDI
(AJB)
Part I: MDE – Model Driven Engineering
2: 1/2: MDE I: Metamodeling. DSL and UML profiles, MDA technologies (XMI, Eclipse, EMF/GMF) (AJB/BRE)
Part II: SSS – Service Science and Service/SOA technologies
3: 8/2: SSS I: Service science (top down) - Service and SOA Technologies (bottom up) (AJB)
Part I continued: MDE – Model Driven Engineering
4: 15/2: MDE II: Model transformations with MOFScript, ATL and other technologies (GO/JO)
5 :22/2: MDE III: Code generation with MOFScript, ATL and other technologies (GO/JO)
Part III: MOS – Modeling of Services - with SoaML
6: 1/3: MOS I: Business Process Modeling (CIM) - with BPMN 2.0, and BMM, EA with UPDM (AJB)
7: 8/3: MOS II: Soaml, UML2 and SysML, Modelio SOA and Scope, –Collaboration and Component models (AJB)
8: 15/3: MOS III: SoaML (PIM) and Requirements modeling , CIM->PIM and SoaML (AJB)
9: 22/3: MOS IV: Method Engineering and SPEM / EPF - for Service systems (BRE)
EASTER
Part IV – Model Driven Interoperability
10: 12/4: MS V: SOA and Service Design, MDA and ADM - Intro to MDI (AJB )
11: 19/4: MDI I: Semantic Web with Ontologies and Model Driven Interoperability (TIR)
12: 26/4: MDI II: Semantic Services and Model Driven Interoperability (TIR)
13: 3/5: MDE IV: Evolution and industrial practice of modelbased technologies (AJB++)
14: 10/5: Course summary and preparation for Exam 31/5 (AJB)
Exam: May 31st, 2010 (Monday), 0900-1200 (3 hours)
19.04.2010
2
ICT
Agenda
ADM
Architecture Driven Modernisation
Patterns
GRASP patterns
Design principles
Design Patterns
Refactoring
ICT
ADM – Architecture-Driven
Modernization (Reverse MDA)
19.04.2010
4
ICT
Data
(What)
Function
(How)
Network
(Where)
People
(Who)
Time
(When)
Motivation
(Why)
Scope
(Contexts)
Business
(Concepts)
System
(Logic)
Technology
(Physics)
Component
(Assemblies)
List of things
important
to business
List of processes
that the business
performs
List of locations
which the business
operates
List of organizations
important to the
business
List of events/cycles
important to the
business
List of business
goals/strategies
Semantic Model
Business
Process
Model
Business
Logistics
System
Workflow
Model
Master
Schedule
Business
Plan
Logical Data ModelApplication
Architecture
Distributed
System
Architecture
Human
Interface
Architecture
Process
Structure
Business Rule
Model
Physical Data Model System DesignTechnology
Architecture
Presentation
Architecture
Control
Structure
Rule
Design
Data Definition ProgramNetwork
Architecture
Security
Architecture
Timing
Definition
Rule
Definition
Operation
(Instances)Data Function Network Organization Schedule Strategy
BMM
SBVR
VDM OSMSBVR
DTFV
BPMN
UMLIMM
(CWM)
CMPM
SoaML
ODM
Business architecture models in OMG
in the Zachman framework
ICT
IT Architecture Ecosystem
19.04.2010
9
ICT
Convergence to Cloud Computing
Adaptive Data
CentersIBM, HP, Sun
Infrastructure
as a ServiceAmazon.com
Cloud
Computing
VirtualizationVMware, Citrix
Software
as a ServiceSaleforce.com
Platform
as a ServiceGoogle, Microsoft
Utility
ComputingRackspace,
Terremark,
Savvis, IBM
GridsUniva Ud,
Gigaspaces,
IBM
Enterprise AppsMicrosoft, IBM, Oracle,
Tibco
Desktop as a
ServiceSimtone, Desktone
Desktop
AppsGoogle, Zoho
ICT
Cloud Computing Definition
“Cloud computing is a model for enabling convenient, on-demand
network access to a shared pool of configurable computing
resources (e.g., networks, servers, storage, applications, and
services) that can be rapidly provisioned and released with
minimal management effort or service provider interaction. This
cloud model promotes availability and is composed of five essential
characteristics, three service models, and four deployment models”.
5: On-demand self-service, Broad network access, Resource
pooling, Rapid elasticity, Measured Service
3: IaaS, PaaS, SaaS
4: Private, Community, Public, Hybrid
NIST
Definition of Cloud Computing, Draft version 15, Oct 7, 2009
http://csrc.nist.gov/groups/SNS/cloud-computing/index.html
19.04.2010
10
ICT
Government Cloud Framework
ICT
Service Model Overview
SaaS
To use the provider’s applications running on a cloud
infrastructure and accessible from various client
devices through a thin client interface such as a Web
browser
Citizen Engagement (Wikis,
Blogs, Data.gov)
Government Productivity (Cloud
based tools)
Business Enablement
(Salesforce.com)
Enterprise Applications (Core
Mission & Business Svcs
PaaS
To deploy onto the cloud infrastructure consumer-
created applications using programming languages
and tools supported by the provider (e.g., java,
python, .Net)
Database and Database
Management Systems
Developer / Testing Tools
Virtual Environments
IaaS
To provision processing, storage, networks, and
other fundamental computing resources where the
consumer is able to deploy and run arbitrary
software, which can include operating systems and
applications
• Computing
• Storage
• Application hosting
Model Capability Provided Example Services
19.04.2010
11
ICT
REMICS Overall process
Recover
Legacy
Artifacts
Source
Architecture MigrateTarget
Architecture
for Service
Cloud platform
Forward MDA
through
PIM4Cloud
Service
Cloud
Implementa
tion
Model Driven
Interoperability
Validate,
Control and
Supervise
Knowledge: REMICS KDM
Business Process and Rules
Components: SoaML
Implementation: UML, U2TP
Knowledge Discovery,
Reverse Engineering
Source code, binaries,
documentation, users
knowledge, configuration files,
execution logs and traces.
SOA and Cloud Computing
Patterns applied,
Legacy Components Replacement
and Wrapping,
Design by Service Composition
Service mediation for
adaptation
SoaML with REMICS extensions
for Service Clouds,
Links to Business Models
Model Transformation, Code
Generation, Traceability
RESERVOIR, Joyant, Amazon,
Google, Microsoft
Models@Runtime for application
management,
Model Checking, Model-based
Testing for validation
ICT
REMICS Metamodel extensions
19.04.2010
12
ICT
Analysis(Domain)Patterns
Architecture Patterns (Macro Architecture)
Design Patterns (Micro Architecture)
Domain Framework
(OO) Reusable Components
Analysis Design Implementation
Idioms(Languagedependentpatterns)
Patterns: From Analysis to
Implementation
ICT
Patterns on various design levels
Object level patterns: GRASP
Collaboration level patterns: Design Patterns
Module level patterns: Architecture Patterns
Refa
cto
ring
19.04.2010
13
ICT
General Responsibility Assignment
Software Patterns.
Responsibility assignment.
1. knowing (answering)
2. or, doing
Guidance and evaluation in
mechanistic design.
1. Expert2. Creator3. Controller4. Low Coupling5. High Cohesion6. Polymorphism7. Pure Fabrication8. Indirection9. Don’t Talk to
Strangers
ICT
Patterns – Abstract Factory
19.04.2010
14
ICT
Design patterns
(with UML & Java examples)
Based on: Gamma/Helm/Johnson/Vlissides (GoF): Design Patterns, 1995
R. Ryan:, D. Rosenstrauch:Design Patterns in Java, 1997
ICT 28
What are patterns?
"A solution to a problem in a context"?
Insufficient, says the “Gang of Four” (GOF)
What’s missing? 3 things:
Recurrence
Teaching (e.g., implementation consequences, trade-offs, and variations)
A name
GOF:
Patterns contain 4 essential elements
pattern name
problem
solution
consequences
Christopher Alexander (as quoted in the GOF book):
"Each pattern describes a problem which occurs over and over again ... and then
describes the core of [a] solution to that problem, in such a way that you can use
this solution a million times over, without ever doing it the same way twice."
19.04.2010
15
ICT
Design Pattern
A design pattern describes a basic scheme for structuringsubsystems and components of a software architecture aswell as their relationships. It identifies, names, and abstractsa common structural or functional principle by describingits different parts, their collaboration and responsibilities.
ICT
GOF (Gang of Four) 23
Patterns
Creational Patterns (5)
Abstract Factory, Builder, Factory Method, Prototype,
Singleton
Structural Patterns (7)
Adapter, Bridge, Composite, Decorator, Façade,
Flyweight, Proxy
Behavioural Patterns (11)
Chain of responsibility, Command, Interpreter,
Iterator, Mediator, Memento, Observer, State,
Strategy, Template method, Visitor
19.04.2010
16
ICT 31
Skylight Spelunker
“Skylight Spelunker” is a Java framework for a file browser
similar in appearance to the “Windows Explorer” included
with Windows 98.
Spelunker has two views:
Disks and folders in tree structure (FolderView - Left pane)
All contents of selected folder (ContentsView - Right pane)
Spelunker provides support for :
Multiple ways of arranging ContentsView icons
Accessing network drives as well as local
Deleting, renaming and viewing disk contents
ICT 32
Windows Explorer Screen Shot
FolderView ContentsView
19.04.2010
17
ICT 33
Patterns in Spelunker example
Composite
used to model the file tree data structure
Strategy
used to layout the file and folder icons in ContentsView
Observer
used to re-display FolderViews and ContentsViews after user
requests
Proxy and State
used to model password-protected network disk drives
Command
used to carry out user requests
ICT 34
The “Composite” pattern
Problem
What is the best way to model the Spelunker file tree?
The Spelunker file tree is a classic tree structure.
Thus we need a leaf class (File) and a tree class (Folder)
which contains pointers to the Files and Folders in it.
However, there are many operations that are relevant
to both a File and a Folder (e.g., getSize()).
The user doesn’t treat Files and Folders differently,
so why should calling modules have to?
The design would be less complex and more flexible
if the calling module could initiate operations on a target object,
without knowing whether the target was a File or a Folder.
File and Folder should share a common interface.
19.04.2010
18
ICT 35
The “Composite” pattern
How the pattern solves the problem
Intent
“Compose objects into tree structures to represent part-whole
hierarchies. Composite lets clients treat individual objects and
compositions of objects uniformly.” [GHJV94]
Explanation
The Composite pattern works by having leaf and tree objects share a
common interface.
Create an abstract base class (or interface) that represents both File
and Folder.
Files and Folders need to provide implementations for the same
operations, but they can implement them differently.
E.g., leaves usually handle an operation directly, while trees usually
forward the operation to its children (and/or perform additional work
before or after forwarding)
ICT 36
The “Composite” pattern
How the pattern solves the problem, cont.
Gang of Four UML [GHJV94]
children
Leaf
Operation( )
Client
Composite
Operation( )
Add(Component)
Remove(Component)
GetChild(int)
Component
Operation( )
Add(Component)
Remove(Component)
GetChild(int)
for all g in children
g.Operation();
19.04.2010
19
ICT 37
The “Composite” pattern
Use of the pattern in Spelunker
Both File and Folder share a common interface: Node.
Spelunker UML
children
File
getSize( )
Resource Tree
Folder
getSize()
getContents()
Node
getSize( )
size =
total of size
of each child
ICT 38
The “Composite” pattern
Use of the pattern in Spelunker, cont.
Code examplespublic class File extends Node{
private long size = 0;
public long getSize(){
return size;}
}
public class Folder extends Node{
private Vector contents;
public long getSize(){
long size = 0;
if (contents != null) {Enumeration e = contents.elements();while (e.hasMoreElements()) {
size += ((Node)e.nextElement()).getSize();}
}return size;
}}
19.04.2010
20
ICT 39
The “Strategy” pattern
Problem
The way in which the icons are arranged varies according to user
preference - the user may choose an iconic view only, or a
short/long detail view.
Including the algorithms to arrange the icons as methods in
ContentsView would make it cumbersome to add new icon
arrangement algorithms to ContentsView; ContentsView would
have to be subclassed and some implementation details might
have to be unnecessarily exposed.
A switch statement would most likely be used to choose the
correct arrangement algorithm.
ICT 40
The “Strategy” pattern
How the pattern solves the problem
Intent
“Define a family of algorithms, encapsulate each one, and make them
interchangeable. Strategy lets the algorithm vary independently from
clients that use it.” [GHJV94]
Explanation
The algorithms for arranging the icons are encapsulated into a
separate interface.
The correct arrangement algorithm is chosen polymorphically.
ContentsView neither knows nor cares which arrangement is
presently in use.
19.04.2010
21
ICT 41
The “Strategy” pattern
How the pattern solves the problem, cont.
Gang of Four UML [GHJV94]
Strategy
AlgorithmInterface()
ConcreteStrategyC
AlgorithmInterface()
ConcreteStrategyB
AlgorithmInterface()
Context
ContextInterface()
strategy
ConcreteStrategyA
AlgorithmInterface()
ICT 42
The “Strategy” pattern
Use of the pattern in Spelunker ContentsView delegates the task of arranging the icons to ViewManager.
Spelunker UML
ViewManager
updateVisibleNodes()
ListViewManager
updateVisibleNodes()
IconViewManager
updateVisibleNodes()
ContentsView
updateVisibleNodes()
strategy
19.04.2010
22
ICT 43
The “Strategy” pattern
Use of the pattern in Spelunker, cont.
Code examples
public class ContentsView extends ResourceTreeView
{
private ViewManager viewManager;
public void showIconView()
{
viewManager = new IconViewManager(this);
}
public void showListView(boolean showDetail)
{
viewManager = new ListViewManager(this, showDetail);
}
public void updateVisibleNodes(Folder activeFolder)
{
viewManager.updateVisibleNodes(activeFolder);
}
}
public interface ViewManager
{
public void updateVisibleNodes(Folder activeFolder);
}
ICT 44
The “Observer” pattern
Problem
What is the best way to keep all views of the file tree in sync?
We need to be able to re-draw the display window after the user
modifies a file/folder (e.g., when user clicks on a folder to select it)
However, there may be several windows and panes that display the
same file/folder. We need to re-draw all of them.
To do this, the tree needs to keep a list of all of its views, and notify
each one after a modification is done.
However, the tree and view objects might:
have little other relationship besides this notification
need to have their code modified independently
need to be reused separately
So it would be preferable not to make them too tightly coupled to each
other.
19.04.2010
23
ICT 45
The “Observer” pattern
How the pattern solves the problem
Intent
“Define a one-to-many dependency between objects so that when one
object changes state, all its dependents are notified and updated
automatically.” [GHJV94]
Explanation
The Observer pattern works by defining an abstract class (or
interface) with a single method signature. The method will be used as
a mechanism for “observer” objects to be notified of changes in their
“subject”.
Concrete observer sub-classes will each provide their own
implementation of what to do when the notification occurs.
The subject can notify each observer the same way, without caring
which specific sub-class of observer the object actually is.
ICT 46
The “Observer” pattern
How the pattern solves the problem, cont.
Gang of Four UML [GHJV94]
subject
observers
Observer
Update( )
Subject
Attach(Observer)
Detach(Observer)
Notify( )
ConcreteSubject
SubjectState
GetState( )
ConcreteObserver
ObserverState
Update( )
return SubjectStateObserverState = subject.GetState()
for all o in observers
o.update();
19.04.2010
24
ICT 47
The “Observer” pattern
Use of the pattern in Spelunker
ResourceTree notifies all ResourceTreeViews whenever its
state is modified.
Spelunker UMLResourceTreeObserver
subject
observers
resourceTreeChanged(Folder)
ResourceTree
activeFolder
AttachObserver(ResourceTreeObserver)
DetachObserver(ResourceTreeObserver)
NotifyObservers( )
ResourceTreeView
updateVisibleNodes(activeFolder);
repaint();Enumeration e = observers.elements();
while (e.hasMoreElements()) {
ResourceTreeObserver o = (ResourceTreeObserver)e.nextElement();
o.resourceTreeChanged(activeFolder);
}
resourceTreeChanged(
Folder activeFolder)
ICT 48
The “Observer” pattern
Use of the pattern in Spelunker, cont. Code examples
public class ResourceTree {private Vector observers;
public void setActiveFolder(Folder folder){
if (activeFolder != folder) {activeFolder = folder;notifyObservers();
}}
public void notifyObservers(){
Enumeration e = observers.elements();while (e.hasMoreElements()) {
((ResourceTreeObserver)e.nextElement()).resourceTreeChanged(activeFolder);}
}}
public abstract class ResourceTreeView extends Panel implements ResourceTreeObserver {
public void resourceTreeChanged(Folder activeFolder){
updateVisibleNodes(activeFolder);repaint();
}}
19.04.2010
25
ICT 49
The “Proxy” pattern
Problem
Network drives might require the user to login before the drive can
be accessed - however, the protocol for accessing a network drive
when logged in might not differ from accessing a local drive.
LocalDrive should not contain network code - this code should be
moved to a separate class, i.e. NetworkDrive.
Creating NetworkDrive as a subclass of LocalDrive would be
complicated and unwieldy - we would have to check access
everytime a drive operation was requested.
Creating NetworkDrive as a subclass of Folder would force us to
duplicate all drive access operations already in LocalDrive.
ICT 50
The “Proxy” pattern
How the pattern solves the problem
Intent
“Provide a surrogate or placeholder for another object to control
access to it.” [GHJV94]
“A Protection Proxy controls access to the original object.
Protection Proxies are useful when objects should have different
access rights.” [GHJV94]
Explanation
The network protocols necessary for logging in and out are
moved into a subclass of Folder called NetworkDrive.
NetworkDrive contains the code necessary for logging in and
out of a network drive.
After logging in, NetworkDrive delegates drive access requests
to LocalDrive (indirectly through ConnectionState).
19.04.2010
26
ICT 51
The “Proxy” pattern
How the pattern solves the problem, cont.
Gang of Four UML [GHJV94]
Subject
Request()
Proxy
Request()
RealSubject
Request()
realSubject
...
RealSubject->Request();
...
ICT 52
The “Proxy” pattern
Use of the pattern in Spelunker
NetworkDrive acts as a Proxy for a remote LocalDrive.
Spelunker UML
Note:
NetworkDrive delegates to
LocalDrive indirectly through
ConnectionOpenedState.
Folder
getContents()
NetworkDrive
getContents()
LocalDrive
getContents()
realSubject
...
localDrive.getContents();
...
19.04.2010
27
ICT 53
The “Proxy” pattern
Use of the pattern in Spelunker, cont.
Code examples
public class NetworkDrive extends Folder{
private ConnectionState connectionState;
public Vector getContents(Folder folder){
return connectionState.getContents(folder);}
}
public class ConnectionOpenedState extends Object implements ConnectionState{
private LocalDrive localDrive;
public Vector getContents(Folder folder){
return localDrive.getContents(folder);}
}
ICT 54
The “State” pattern
Problem
What is the best way to perform password-protection processing
on network drives?
Network drives need to act differently depending on whether the user
has logged in or not; e.g., the user cannot examine or modify a
network drive until they log in.
This can be accomplished by checking a condition before executing
each operation; e.g., “if (loggedIn())”. But this is ugly code, as well as
being inefficient and repetitive.
This is also difficult to extend: what if we need to implement another
set of checks for another condition; e.g., “if (!disconnected())”?
The design would be less complex and more flexible if we could
isolate in one location all behavior related to a particular state of the
object.
19.04.2010
28
ICT 55
The “State” pattern
How the pattern solves the problem
Intent
“Allow an object to alter its behavior when its internal state changes.
The object will appear to change its class.” [GHJV94]
Explanation
The State pattern works by creating an abstract class (or interface) with
method signatures for every state-dependent operation in the main object, and
concrete sub-classes that provide implementations for these methods. The
main object then delegates each of these operations to the state object it is
currently using.
Each state class can implement each operation in its own way (e.g., perform
unique processing, disallow the operation, throw an exception, etc.).
The main object can change its behavior by changing the state object it is
using.
This is a very clean design - and also extendible: we can simply add new state
classes to add additional behavior, without modifying the original object.
ICT 56
The “State” pattern
How the pattern solves the problem, cont.
Gang of Four UML [GHJV94]
state
Context
Request( )
ConcreteStateB
HandleRequest( )
State
HandleRequest( )
ConcreteStateA
HandleRequest( )
state.HandleRequest()
19.04.2010
29
ICT 57
The “State” pattern
Use of the pattern in Spelunker
The NetworkDrive delegates operations to its
ConnectionState.
Spelunker UML
state
NetworkDrive
getContents()
ConnectionClosedState
getContents( )
ConnectionState
getContents( )
ConnectionOpenedState
getContents( )
return
connectionState.getContents()
changeState(ConnectionState)
ICT 58
The “State” pattern
Use of the pattern in Spelunker, cont.
Code examplespublic class ConnectionClosedState implements ConnectionState {
public void login() {LocalDrive localDrive = null;
// login and initiate localDrive
networkDrive.changeState(new ConnectionOpenedState(networkDrive, localDrive));}
public Vector getContents(Folder folder) {login();return networkDrive.getContents(folder);
}}
public class ConnectionOpenedState implements ConnectionState {public void login() {
// display error}
public Vector getContents(Folder folder) {return localDrive.getContents(folder);
}}
19.04.2010
30
ICT 59
The “Command” pattern
Problem
A request might need access to any number of classes.
The initiator of the request should not be tightly coupled to
these classes.
Requests should be storable to support undoable
operations; therefore, requests must be accessible through
some common interface.
How do we implement requests without coupling them to the
initiator or target, or requiring the initiator to know the
implementation details of the request ?
Implementing the code for all requests in one class would
centralize the application and make it difficult to create new
requests.
ICT 60
The “Command” pattern
How the pattern solves the problem
Intent
“Encapsulate a request as an object, thereby letting you parameterize
clients with different requests, queue or log requests, and support
undoable operations.” [GHJV94]
Explanation
Places the implementation of a request into a separate class.
Initiators of the request do not know any implementation details of the
request - they simply fire it off by calling the execute() method.
The targets of the request do not need to know anything about the
request.
All requests are accessible through a common interface.
The correct implementation is chosen polymorphically.
19.04.2010
31
ICT 61
The “Command” pattern
How the pattern solves the problem, cont.
Gang of Four UML [GHJV94]
Command
Execute()
ConcreteCommand
Execute()
Receiver
Action()receiver
Client Invoker
receiver->Action();
state
ICT 62
The “Command” pattern
Use of the pattern in Spelunker
Used to implement user operations on files and folders.
Spelunker UML
Command
execute()
DeleteCommand
execute()
ContentsView
getSelectedNodes()receiver
Skylight
Spelunker
CommandButton
...
Vector selectedNodes = contentsView.getSelectedNodes();
...
if (!node.deleteNode(node)) {
...
19.04.2010
32
ICT 63
The “Command” pattern
Use of the pattern in Spelunker, cont. Code examples
public class CommandButton extends Button {private Command command;
public CommandButton(String label, Command command) {super(label);this.command = command;
}
public boolean action(Event e,Object what) {
command.execute();return super.action(e, what);
}}
public class DeleteCommand extends Command {private ContentsView contentsView;private ResourceTree resourceTree;
public void execute() {(code for retrieving all selected Nodes
from ContentsView and deleting them)}
}
public abstract class Command extends Object {public abstract void execute();
}
ICT
Basis Litteratur (Pattern kataloger)
Design Patterns, Elements of Reusable Object-Oriented SoftwareGamma et. al. Addison-Wesley, ISBN 0-201-63361-2
Analysis Patterns, Reusable Object ModelsMartin Fowler, Addison-Weslwy, ISBN 0-201-89542-0
Pattern-Oriented Software ArchitectureF. Buschmann et. al, J. Wiley, ISBN 0-471-95869-7
http://st-www.cs.uiuc.edu/users/patterns/patterns.html
http://c2.com/ppr/index.html
AntiPatterns - Refactoring Software, Architectures, and Projects in CrisisW. Brown et. al, J. Wiley, ISBN 0-471-19713-0
19.04.2010
33
ICT
Tilleggs litteratur
Design Patterns for Object-Oriented Software Development,Pree, Addison-Wesley, ISBN 0-201-42294-8, 1995
CORBA Design Patterns, T. Mowbray, R. Malveau, j. Wiley, 1997, ISBN 0-471-15882-8
Communications of ACM, “Software Patterns” - special issueOctober 1996, Vol. 39, Number 10
Pattern Languages of Program Design 1J. Coplien, Douglas SchmidtAddison-Wesley, ISBN 0-201-60734-4, 1995
Pattern Languages of Program Design 2J. Vlissides, J. Coplien, N. KerthAddison-Wesley, ISBN 0-201-89527-7, 1996
ICT
Refactoring - Improving the design of
existing code 1. Refactoring - a first example
2. Principles in refactoring
3. Bad Smells in Code
4. Building Tests
5. Toward a catolog of refactorings
6. Composing Methods
7. Moving Features between objects
8. Organizing data
9. Simplifying Conditional Expressions
10. Making Method calls simpler
11. Dealing with Generalization
12. Big Refactorings
13. Refactoring, Reuse and Reality
14. Refactoring tools
M. Fowler, with K. Beck, J. Brant, W. Opdyke, D. Roberts, Addison-Wesley, August 1999
Refactoring: Improving the design of existing code
19.04.2010
34
ICT
Refactoring - What and
Why ?
Refactoring is the process of changing a software
system in such a way that it does not alter the external
behaviour of the code yet improves its internal
structure.
Improving to make it easier to understand and cheaper
to modify
ICT
When should you
refactor
The rule of three - Three strikes and you refactor
Refactor when you add function
Refactor when you need to fix a bug
Refactor as you do a code review
19.04.2010
35
ICT
Why refactoring
works
Programs that are hard to read are hard to modify
Programs that have duplicated logic are hard to modify
Program that require additional behaviour that requries
you to change running code are hard to modify
Programs with complex conditional logic are hard to
modify
We want programs that are easy to read, that have all
logic specified in one and only one place, do not allow
changes to endanger existing behaviour, and allow
conditional logic to be expressed as simply as possible
ICT
Refactoring
strategies
Composing Methods
Moving features between objects
Organizing data
Simplifying conditional expressions
Making method calls simpler
Dealing with generalization
Big refactorings
19.04.2010
36
ICT
Composing
Methods
Extract method
Inline method
Inline temp
Replace temp with query
Introduce explaining variable
Split temporary variable
Remove assignments to parameters
Replace method with method object
Substitute algorithm
ICT
Moving Features between
objects
Move method
Move field
Extract Class
Inline Class
Hide Delegate
Remove middle man
Introduce foreign method
Introduce local extension
19.04.2010
37
ICT
Bad Smells in
Code (1/4)
Duplicated Code (extract method, extract class, pull
up method, form template method)
Long Method (extract method, replace temp with
query, replace method with method object,
decompose conditional)
Large Class (extract class, extract subclass, extract
interface, replace data value with object)
Long ParameterList (replace parameter with method,
introduce parameter object, preserve whole object)
Divergent Change (extract class)
ICT
Bad Smells in
Code (2/4)
Shotgun Surgery (move method, move field, inline class)
Feature Envy (move method, move field, extract field)
Data Clumps (extract class, introduce parameter object,
preserve whole object)
Primitive Obsession (replace data value with object, extract
class, introduce parameter object, replace array with object,
replace type code with class/subclasses, replace type code
with state/strategy)
Switch Statements (replace conditional with polymorphism,
replace type code with subclasses/state/strategy, replace
parameter with explicit methods, introduce null object)
19.04.2010
38
ICT
Bad Smells in
Code (3/4)
Parallell Inheritance Hierarchies (move method,
move field)
Lazy Class (inline class, collapse hierarchy)
Speculative Generality (collapse hierarchy, inline
class, remove parameter, rename method)
Temporary Field (extend class, introduce null
object)
Message Chains (hide delegate)
Middle Man (remove middle man, inline method,
replace delegation with inheritance)
Inappropriate Intimacy (move method, move field,
change bidirection to unidirectional)
ICT
Bad Smells in
Code (4/4)
Alternative classes with different interfaces (rename
method, move method)
Incomplete Library Class (introduce foreign
method, introduce local extension)
Data Class (move method, encapsulate field,
encapsulate collection)
Refused Bequest (replace inheritance with
delegation)
Comments (extract method, introduce assertion)
19.04.2010
39
ICT
Organizing data Self encapsulate field
Replace data value with object
Change value to reference
Change reference to value
Replace array with object
Duplicate observed data
Change unidirectional association to bidirectional
Change bidirectional association to unidirectional
Replace magic number with symbolic constant
Encapsulate field
Encapsulate collection
Replace record with data class
Replace type code with class/sublasses
Replace type code with state/strategy
Replace subclass with fields
ICT
Simplifying Conditional
Expressions
Decompose conditional
Consolidate conditional expression
Consolidate duplicate conditional fragments
Remove control flag
Replace nested conditional with guard clauses
Replace conditional with polymorphism
Introduce null object
Introduce assertion
19.04.2010
40
ICT
Making Method calls simpler
Rename method
Add parameter
Remove parameter
Separate query from modifier
Parameterize method
Replace parameter with explicit methods
Preserve whole object
Replace parameter with method
Introduce parameter object
Remove setting method
Hide method
Replace constructor with factory method
Encapsulate downcast
Replace error code with exception
Replace exception with test
ICT
Dealing with Generalization
Pull up field
Pull up method
Pull up constructor body
Push down method
Push down field
Extract subclass
Extract superclass
Extract interface
Collapse hierarchy
Form template method
Replace inheritance with delegation
Replace delegation with inheritance
19.04.2010
41
ICT
Big refactorings
Tease apart inheritance
Convert procedural design to objects
Separate domain from presentation
Extract hierarchy
ICT
The rhythm of
refactoring ...
test, small change, test, small change, test, ….
… allows refactoring to move quickly and safely
19.04.2010
42
ICT
AntiPatterns
Refactoring Software, Architectures , and Projects in
Crisis: W. Brown, R. Malveau. H. McCormick, T. Mowbray, Wiley, 1998
AntiPattern: A commonly occuring patterns or solution that generates decidely
negative consequences. An AntiPatterns may be a pattern in the wrong context.
When properly documented, an AntiPattern comprises a paired AntiPattern
solution with a refactored solution.
ICT
Software Development
AntiPatterns The Blob (from the film)
Continuous Obsolescence
Lava Flow
Ambiguous Viewpoint
Functional Decomposition
Poltergeists
Boat Anchor
Golden Hammer
Dead End
Spaghetti Code
Input Kludge
Walking through a Minefield
Cut-and-Paste Programming
Mushrooom management
19.04.2010
43
ICT
Software Architecture
AntiPatterns Autogenerated Sovepipe
Stovepipe Enterprise
Jumble
Stovepipe System
Cover your Assets
Vendor Lock-In
Wolf Ticket
Architecture by Implication
Warm bodies
Design by Committee
Swiss Army Knife
Reinvent the Wheel
The Grand Old Duke of York
ICT
Software Project Management
AntiPatterns
Blowhard Jamboree
Analysis Paralysis
Viewgraph Engineering
Death by Planning
Fear of Success
Corncob
Intellectual Violence
Irrational Management
Smoke and Mirrors
Project Mismanagement
Throw it over the wall
Fire Drill
The Feud
E-mail is dangerous
19.04.2010
44
ICT
Practical Refactoring
exercise
ICT
Example:Video rental
Bad smells:
Long Method
Feature Envy
Switch statements
Temporary Fields
Support change ?: Add HTML
statement, change classification of
films
Customer1
+ statement()
Rental1
daysRented : int
0..* 10..* 1
Movie1
priceCode : int
1 0..*1 0..*
19.04.2010
45
ICT
extract from
statement()
public String statement() {
/ ….. Determine amounts for each rentalSwitch (each.getMovie().getPriceCode()) {case Movie.REGULAR thisAmount += 2;
…..
// add frequent renter pointsfrequentRenterPoints ++;
if (each.getMovie().getPriceCode() -----
// show figures for this rental
// add footer lines
}
ICT
Refactorings:Video
rental
Create Tests to check refactoring correctness
Decomposing and redistributing the statement
method (extract method, moving the amount
calculation amountFor() (move the method from
customer to rental), rename variables (I.e each ->
aRental)
similar: extracting frequent renter points, removing
temps (totals) replaceTempWithQuery
totalAmount/freqRentPoint,
19.04.2010
46
ICT
Extracting and Moving
methods
Customer1
+ statement()
Rental1
daysRented : int
getCharge()
getFreqRentPoints()0..* 10..* 1
Movie1
priceCode : int
1 0..*1 0..*
Customer1
+ statement()
+ getTotalCharge()
+ getTotFreqRentPoints()
Rental1
daysRented : int
getCharge()
getFreqRentPoints()0..* 10..* 1
Movie1
priceCode : int
1 0..*1 0..*
ICT
Move calculation of charge
and points
to the “expert”
Customer1
+ statement()
+ getTotalCharge()
+ getTotFreqRentPoints()
Rental1
daysRented : int
getCharge()
getFreqRentPoints()0..* 10..* 1
Movie1
priceCode : int
getCharge(days : int)
getFreqRentPoints(days : int)
10..*10..*
19.04.2010
47
ICT
Refactorings:Video
rental
replace conditional logic on price code with
polymorphism, using inheritance - problem: a movie
can change its classification during its lifetime -> use
the state pattern for price code object (or strategy) ->
replace type code with state/strategy, move method
(switch into price class), replace conditional with
polymorphism to eliminate switch
ICT
Customer1
+ statement()
+ getTotalCharge()
+ getTotFreqRentPoints()
+ htmlstatement()
Rental1
daysRented : int
getCharge()
getFreqRentPoints()0..* 10..* 1
ChildrensPrice
getCharge(days : int)
NewReleasePrice
getCharge(days : int)
getFreqRentPoints(days : int)
RegularPrice
getCharge(days : int)
Movie1
priceCode : int
getCharge(days : int)
getFreqRentPoints(days : int)
1
0..*
1
0..*
Price
getCharge(days : int)
getFreqRentPoints(days : int)11
top related