chapter 9 behavioral design patterns

Chapter 9Behavioral Design Patterns

Process Phase Affected by This ChapterRequirementsAnalysis

Design

Implementation

ArchitectureFramework Detailed Design

xKey: = secondary emphasisx = main emphasis

Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

Design Purpose

Interpret expressions written in a formal grammar.

Design Pattern Summary

Represent the grammar using a

Recursive design pattern form: Pass

interpretation to aggregated objects.

Interpreter


Interpreter Client Interface

AbstractExpressioninterpret()

Client


Interpreter Design Pattern

AbstractExpressioninterpret()

Client

TerminalExpressioninterpret()

NonTerminalExpressioninterpret()

1..n


interpret()

Interpreter Sequence Diagram

TerminalExpression

:NonterminalExpression:Client AbstractExpression

NonterminalExpression

...

create & interpret()

create & interpret()

...

...


Example of a Virtual Machine “Program”

260Mhz & 64MB

400Mhz & 128MB

260Mhz & 32MB

assemble ….

Graphics reproduced with permission from Corel.Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

Input For Network Assembly Example


Output of Network Assembly Example (1 of 3)


Design Goal At Work: Flexibility ,

Correctness, Reuse

Separate the processing of each part of the network order.


Interpreter Design Pattern

Componentassemble()

NetSystemassemble()

component1

Client


Application of Interpreter Design Pattern

Componentassemble()

Computerassemble()

NetSystemassemble()

component1

component2

RAMdescribe()

CPUdescribe()

cpu

ram

Client

SetupgetInputFromUser()

parse()

1

0..1


Key Concept: Interpreter Design Pattern

-- a form for parsing and a means of processing expressions.


- given a collection of objects

e.g.,

o the videos in a video store

o a directory

- having specified ways to progress through them

e.g.,

o “list in alphabetical order”

o “list all videos currently on loan”

... encapsulate each of these ways

Aggregate object

Purpose of Iterator

iterator2

iterator7


Design Purpose (Gamma et al)

Provide a way to access the elements of an

aggregate object sequentially without

exposing its underlying representation.


Encapsulate the iteration in a class pointing

(in effect) to an element of the aggregate.

Iterator


Using Iterator Functions

/*

To perform desiredOperation() on elements of

the aggregate according to the iteration (order) i:

*/

for( i.setToFirst(); !i.isDone(); i.increment() )

desiredOperation( i.getCurrentElement() );


Functions for Iterator

// Iterator "points" to first element:

void setToFirst();

// true if iterator "points" past the last element:

boolean isDone();

// Causes the iterator to point to its next element:

void increment();

// Return the element pointed to by the iterator:

C getCurrentElement(); Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

Iterator Operations

Set to beginning Increment Get current

elementCheck not done yet

The Iterator

Index (integer) i on

array myArrayi = 0 ++i myArray[ i ]

i < myArray.length

Index (integer) j on

VectormyVector

j = 0 ++jmyVector

.get( j )j < myVector

.size()

Iterator (object)myIterator

myIterator.setToFirst()

myIterator.increment()

myIterator.getCurrent Element()

! myIterator.isDone()

Iterator in Arrays, Vector, and in General


Imagining Iterator

iterator:Iterator

element:Element

Aggregate of Elementobjects

Key: Intended sequence of Element objects

After first() executes, iterator references this object.

After increment() executes, iterator references this object.

Before increment() executes, iterator references this object.


Iterator Example Setup Code

// Suppose that we have iterators for forward and

// backward order: we can re-use print_employees()

List employees = new List();

ForwardListIterator fwd // to go from front to back

= new ForwardListIterator ( employees );

ReverseListIterator bckwd // to go from back to front

= new ReverseListIterator ( employees );

client.print_employees( fwd ); // print from front to back

client.print_employees( bckwd ); // print from back to front


Iterator Class Model

Aggregate

Client

IteratorsetToFirst()increment()

isDone()getCurrentItem()

ConcreteIterator ConcreteAggregateAggregatedElement 1…n1


An Organizational Chart Example

Vanna Presleyvice president, 4 years

Sue Millersvce. mgr., 7 years

Sam Markhamsvce. mgr., 5 years

Sal Monahansvce. mgr., 1 year

Iolanthe Carpind. contrib., 8

Inge Carlsonind. contrib., 12

Inez Clappind. contrib., 11

Inky Conwayind. contrib., 6


Iterating by Organizational Seniority Over a Bank Organization


Iterating by Years of Service Over an Organization Chart


Design Goal At Work: Flexibility ,

Correctness

Separate the “visiting” procedure from the processing of individual employees.


Class Structure for Iterator Example

ServiceIterator

OrgSeniorityIterator

OrgChartDP OrgChartIteratorDP

Teller

Employeedisplay()

Supervisor

Client Setup

OrgChartIteratorfirst()next()isDone()currentItem()


Computing next()

root

1

4 5 6

9 10

2 3

7 8

11 12

( 1, 2, 0, 0 ) // my distance from the end of my sibling list )

DeepRoot

doneNode( 1 ) ( 0 )


main()

Sequence Diagram for Encounter Foreign Character

Use CaseUser Employee

display( OrgCharIterator )

display()

first(), next(), idDone(), getItem() etc.

Employee

OrgChartIterator :Client

AlphabeticalOrgChartIterator

:Setup

Get org chart as in Composite example tbd

getTheIterator()


Computing next()

root

1

4 5 6

9 10

2 3

7 8

11 12

( 1, 2, 0, 0 )

DeepRoot

doneNode( 1 ) ( 0 )

“distance from the end of my sibling list”

( 1, 2, 0 )

( 1, 2 )


main()

Iterator Example Sequence Diagram

User Employee

display( OrgCharIterator )

display()

first(), next(), isDone(), getItem() etc.

Employee

OrgChartIterator :Client

AlphabeticalOrgChartIterator:Setup

Get org chart as in Composite example tbd

getTheIterator()


Iterator in the Java APICollection

Iterator iterator()

Iteratornext()hasNext()remove()

ListIterator List AbstractCollection

AbstractListListIterator listIterator()

Iter*

ListItr*

* IBM implementationArrayList Vector


Output for Iteration on a Java ArrayList


Address Book Application Using Java Iterator

CollectionIterator iterator()

Iteratornext()

hasNext()remove()

ListIterator List

AbstractListListIterator listIterator()

ListItr*

ArrayList

NameAddrEntry AddressBook0..n

This application

Key:

Java API


Iterator Class Model

ConcreteIterator

ClientAggregate

createIterator( )

IteratorsetToFirst()increment()isDone()getCurrentItem()

ConcreteAggregate

createIterator( )

return new ConcreteIterator( this );

OLD


Output for StringTokenizer Example


Key Concept: Iterator Design Pattern

-- to access the elements of a collection.


Solicitation of Customer Information 1 of 2

Name and Location

Basic information


Solicitation of Customer Information 2 of 2

Account Information

Additional information

Customer ID

Total business

Amount due


Design Purpose

Avoid references between dependent objects.


Capture mutual behavior in a separate class.

Mediator


The Mediator Class Model

Mediator Colleague

ConcreteMediator

ConcreteColleague1 ConcreteColleague2


:ConcreteMediator

:ConcreteColleague1 :ConcreteColleague2

:Mediator2. Initiation on a ConcreteColleague

doPart1()

doPart2()

1. Initiation by ConcreteMediator

mediate()

mediate()

doSome1()

doSome2()

Mediator Sequence Diagrams


Design Goal At Work: Reusability and

Robustness

Avoid hard-coded dependencies among the game’s GUI classes, enabling their use in other contexts.


Application of Mediator To Customer Information Application

CustomerDisplay

:BasicInfoGUI:

CustomerGUI

:CustTypeDisplay :CustInfoDisplay


The Mediator Class Model in the Java API

ComponentListeneractionPerformed()

ComponentaddComponentListener()

MyEventListener

MyComponent1 MyComponent2


Key Concept: Mediator Design Pattern

-- to capture mutual behavior without direct dependency.


Design Purpose

Arrange for a set of objects to

be affected by a single object.


The single object aggregates the set, calling a

method with a fixed name on each member.

Observer


Observer Design Pattern

Sourcenotify()

Observerupdate()

for all Observer’s o:o.update();

Client of thissystem1

2

1..n

Server part Client part


Observer Design Pattern

Sourcenotify()

Observerupdate()

ConcreteSourcestate

ConcreteObserverobserverState

update()

for all Observer’s o: o.update();

Client

2

3

1..n


1


Observer Applied to International Hamburger Co.

Sourcenotify()

Observerupdate()

Headquartersdemand

SeniorManagementforecastupdate()

Client1..n

MarketingmarketingDemand

update()doDisplay()if( abs( hq.demand - marketingDemand ) > 0.01 )

{ marketingDemand = hq.getDemand();doDisplay();

}



I/O Example for Mutual Fund Observer Example

Note: HiGrowthMutualFund starts with 3 shares of Awesome, assumes price of 1.0, and has non-Awesome holdings totalling 400.0

Note: MedGrowthMutualFund starts with 2 shares of Awesome, assumes price of 1.0, and has non-Awesome holdings totalling 300.0

Note: LoGrowthMutualFund starts with 1 shares of Awesome, assumes price of 1.0, and has non-Awesome holdings totalling 200.0

Enter 'quit': Any other input to continue.

go on

Enter the current price of Awesome Inc. in decimal form.

32.1

Value of Lo Growth Mutual Fund changed from 201.0 to 232.1

Value of Med Growth Mutual Fund changed from 302.0 to 364.2

Value of Hi Growth Mutual Fund changed from 403.0 to 496.3


go on

Enter the current price of Awesome Inc. in decimal form.

21.0

Value of Lo Growth Mutual Fund changed from 232.1 to 221.0

Value of Med Growth Mutual Fund changed from 364.2 to 342.0

Value of Hi Growth Mutual Fund changed from 496.3 to 463.0



Design Goal At Work: Flexibility

Allow mutual funds objects to easily acquire or divest of stocks.


ObservablenotifyObservers()

Observerupdate( Observable, Object )

AwesomeIncprice

LongTermMutualFund….

update(…)

Observer Example:

Mutual Funds

Key:Developer Class

Java API Class

MediumTermMutualFund….

update(…)HiGrowthMutualFund

….update(…)

MutualFundvalue

numAwesomeShares

Client

Setup


ObservablenotifyObservers()

Observerupdate( Observable, Object )

MyObservableMyConcreteObserver

observerStateupdate(…)

Observer in the Java API

subject

Key: Developer ClassJava API Class


Key Concept: Observer Design Pattern

-- to keep a set of objects up to date with the state of a designated object.


Design Purpose

Cause an object to behave in a

manner determined by its state.


Aggregate a State object

and delegate behavior to it.

State


TargetStateBhandleRequest()

TargetdoRequest()

State Design Pattern Structure: doRequest() behaves according to state of Target

targetState TargetStatehandleRequest()

Client

TargetStateAhandleRequest()

1

{ targetState.handleRequest(); }

. . . . . .


GUI For a Role-Playing Video Game

Set Characteristics

Courtesy Tom VanCourt and CorelAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

Design Goal At Work: Correctness and

Reusability

Separate the generic code for handling button clicks from the actions which depend on the game’s status at the time.


State Design Pattern Applied to Role-Playing Game

MyGamesetCharacteristics()

MyGameStatehandleClick()

state

{ state.handleClick(); }

EngaginghandleClick()

SettingUphandleClick()

WaitinghandleClick()

SettingCharacteristicshandleClick()

{ showWindow(); …. // more }

{ showWindow(); …. // more }

{ // already responding … // display message }

{ // do nothing … // display message}


Key Concept: State Design Pattern

-- to cause a object’s functions to behave according to the state it’s in.


Design Purpose

Allow a set of objects to service a request.

Present clients with a simple interface.


Link the objects in a chain via aggregation,

allowing each to perform some of the

responsibility, passing the request along.

Chain of Responsibility


Chain of Responsibility: Object Model

entryHandler:HandlerSubclassX

(next element): HandlerSubclassY

(next element): HandlerSubclassZ

successor successor


HandlerSubclassAhandleRequest()respondA()

Chain of Responsibility Class Model

Client

HandlerSubclassBhandleRequest() respondB()

successor

Handler

handleRequest()

respondA(); // handle some of the required functionality successor.handleRequest(); // pass along remaining responsibility

. . . .


GUI For Customer Information Application


Output for Customer Information Application


Design Goal At Work: Flexibility

Isolate the responsibilities of each part of the input form to generate its XML.


Class Model For User Information Collection

CustomerInfoElement

CustomerName CompanyNameCustomerInfo

CustomerPersonal CustomerProfessionalCustomerAddress Company

container

TextFieldListener«client»

CustomerInfoApp«setup»

Each of these classes supports handleClick()


Object Model Fragment for Customer Information Example

: CompanyName

:Company

:CustomerProfessional

container

:CustomerInfo

handleClick()

container

handleClick()

container

handleClick()


Key Concept: Chain of Responsibility Design Pattern

-- to distribute functional responsibility among a collection of objects.


Design Purpose

Increase flexibility in calling for a service

e.g., allow undo-able operations.


Capture operations as classes.

Command


Target1action1()

The Command Design Pattern

Action2Commandexecute()

Target2action2()

replacedCommand

execute()

Action1Commandexecute()

Client


The Command Design Pattern: Example

MenuItemhandleClick()

Commandexecute()

CutCommandexecute()

Documentcut()

copy()

document

command

CopyCommandexecute()

document

document.cut()

document.copy()

command.execute()


execute()

Sequence Diagram for Document Command Example

:MenuItem

handleClick()

command:Command

:CopyCommand

document:Document

copy()


I/O for Word Processor Undo

Example1 of 2


I/O for Word Processor Undo Example

2 of 2


Design Goal At Work: Flexibility and

Robustness

Isolate the responsibilities of the Word Processor commands, making them save-able and reversible.


Undo Example Class Model

WordProcessorCommand

execute()undo()

CutCommandtextCut: String

offset: int execute()

undo()

Documenttext: String

commandHistory

PasteCommand offset: intlength: intexecute()

undo()

0..n

QuitCommandexecute()

UndoCommandexecute()

document

DocumentCommandgetInputFromUser()document


Key Concept: Command Design Pattern

-- to avoid calling a method directly (e.g., so as to record or intercept it).


• Required to solve equations of the form

ax2 + bx + c = 0.

• Must be able to handle all input possibilities for a, b, and c.

• This is a tutorial application that must provide full explanations to users about the solutions for all values for a, b, and c.

Example of Template Motivation


1. Report progress2. Display number of solutions3. Display first solution, if any 4. Display second solution, if any

A Basic

Quadratic

Algorithm


Design Purpose

Allow runtime variants on an algorithm.


Express the basic algorithm in a base class,

using method calls where variation is

required.

Template


Class Model for Template

TemplateAlgorithmhandleRequest()

nonInheritedMethod()calledMethod1()calledMethod2()

….

Algorithm1calledMethod1()calledMethod2()

….

algorithm


….

Client


….

{ algorithm.handleRequest(); }

SubjectdoRequest()


I/O For Quadratic Example 1/2


I/O For Quadratic Example 2/2


displaySolutions()

{

displayWhatsHappening();

displayNumSolutions();

displayFirstSolutions();

displaySecondSolution();

}

Quadratic Display Algorithm

Override

Override

Override


Design Goal At Work: Flexibility and

Robustness

Isolate the main algorithm for quadratic solution display. Isolate the variants that depend on the coefficients.


NoSolutionsdisplayNumSolutions()displayFirstSolution()

displaySecondSolution()

OneSolutiondisplayNumSolutions()displayFirstSolution()


Class Model for Quadratic Problem

QuadraticEquationfloat a, b, c

solveQuadratic()

QuadraticAlgorithmdisplayWhatsHappening()

displaySolution()inputMakesSense()

displayNumSolutions();displayFirstSolution()


algorithm

TwoSolutionsdisplayNumSolutions()displayFirstSolution()


Client

{ algorithm.displaySolution(); }

SetupgetABC()

InfinitelyManySolutionsdisplayNumSolutions()displayFirstSolution()



Key Concept: Template Design Pattern

-- to capture a basic algorithm and its variants.


Behavioral Design Patterns capture behavior among objects

Interpreter handles expressions in grammers

Iterator visits members of a collection

Mediator captures behavior among peer objects

Observer updates objects affected by a single object

State allows method behavior to depend on current status

Chain of Responsibility allows a set of objects to provide

functionality collectively

Command captures function flexibly (e.g. undo-able)

Template captures basic algorithms, allowing variability

Summary of Behavioral

Patterns


chapter 9 behavioral design patterns

Documents

software design

braude wiley

design goal

recursive design pattern

network order

formal grammar

collection of objects

pass interpretation