Agile Object Oriented Design

SOLID principles

dmitry.kandalov@db.com

Why it is Agile?

?

principles != rules

Single Responsibility

Principle

Problem domain

Conceptual model

Implementation

Problem domain

Conceptual model

Implementation

?

?

NOooo!!

Book

InstrumentPositionvalue: double

1

*1 1

Book PositionListener 1

BookPosNode

Book PositionListener 2

NetworkApplication

position

position

position

BookPosNode

AbstractBookPosNode

Subscriber

SnapshotProvider

HeartbeatMonitor

StateMachine

1

2

3

4

the rest of the class is collapsed

5

the rest of the class is collapsed

Open/Closed Principle

AbstractPositionNode

BookPosNode

Client

AbstractPositionNode

BookPosNode JMSNode

Client PositionWatcher

Add

Change

AbstractPositionNode

BookPosNode JMSNode

Client PositionWatcher

Add

NodeV2

Front-end

Back-end

Database

Change

Liskov Substitution Principle

Ellipse-circle problem

rectangle-square

Point

x, y : int

#equals()#hashCode()

Point

x, y : int

#equals()#hashCode()

ColorPoint

color : Color

#equals()#hashCode()

Point

x, y : int

#equals()#hashCode()

ColorPoint

color : Color

#equals()#hashCode()

Can't extend like this preserving equals contract

(Effective Java, Item 8)

@IViolateLSP

class Dog implements ICanBark …

class Button implements IClickable …

Interface Segregation Principle

<<interface>>

BigService

Client1 Client2 Client3

<<interface>>

BigService

<<interface>>

Service1<<interface>>

Service2<<interface>>

Service3

Client1 Client2 Client3

BookPositionNode

<<interface>>

ResubscribingNode AbsPosNode

StateMachine

Client

uses

uses

Dependency Inversion Principle

Client

Service

client

service

Client

<<interface>>

ServiceServiceImpl

client

service

client

service

Client

<<interface>>

ServiceServiceImpl

client

service

Client<<interface>>

Service

ServiceImpl

client

service

client

service

Client<<interface>>

Service

ServiceImpl

client

service

api

SRP

OCP

LSP

ISP

DIP

Single Responsibility

Principle

Open/Closed Principle

Liskov Substitution Principle

Interface Segregation Principle

Dependency Inversion Principle

What else?

Problem domain

Conceptual model

Implementation

F**k Design

Zen Coding

and only then for computers

Code is written for

people

REP

CRP

CCP

ADP

SDP

SAP

UML,

patterns,

and more...

Thanks!

SRP

OCP

LSP

ISP

DIP

http://weblogs.java.net/blog/82/2003/09/02/aristotles-error-or-agile-smagile

http://blog.objectmentor.com/articles/2009/01/31/quality-doesnt-matter-that-much-jeff-and-joel

http://www.codinghorror.com/blog/archives/000805.htmlhttp://www.youtube.com/watch?v=2k1uOqRb0HU

http://blogs.msdn.com/brada/archive/2003/10/02/50420.aspx

http://www.joelonsoftware.com/articles/LeakyAbstractions.html

http://www.joelonsoftware.com/items/2009/09/23.html