19.12.2006 1

Aspect Oriented Programming

Gülşah KARADUMAN

219.12.2006

Outline

Introduction The Problem Goal of AOP Programming with Aspects AspectJ Conclusions

319.12.2006

Background Information

Functional decomposition Break the system into smaller units

Programming languagesDefine abstractions for the small unitsCompose the units into systems

419.12.2006

Procedure Based Languages

Functional, Procedural, OO Comfortable to talk about what is

encapsulated as a functional unit of the overall system

What about the units of decomposition that are not functional

519.12.2006

Modularity

Abstraction Decomposition Encapsulation Information Hiding Separation of Concerns

Low couplingHigh cohesion

619.12.2006

Concerns

Particular goal, concept, or area of interest Primary motivation for organizing and

decomposing software into manageable and comprehensible parts

719.12.2006

Separation of Concerns

CohesionMaximize cohesion within a component

CouplingMinimize coupling between components

819.12.2006

Separation of Concerns

AdvantagesUnderstandabilityReusabilityExtensibilityMaintainabilityAdaptability

919.12.2006

The Problem

Limitations of OOPdecomposition resulting in cross-cutting

concerns Insufficieny of OO and procedural

development techniques

1019.12.2006

Crosscutting, Scattering, and Tangling Crosscutting

Concerns inherently relating to multiple components

ScatteringSingle concern affecting multiple modules

TanglingMultiple concerns interleaved in a single

module

1119.12.2006

Crosscutting Concern Examples Synchronization Real-time constraints Error-checking Object interaction constraints Memory management Persistency Security Caching Logging Monitoring Testing Domain specific optimization

1219.12.2006

Crosscutting Concern Examples

Display

Figure FigureElement*

Point LinegetX()

getY()

getP1

setP1

DisplayTrackingsetX(int)

setY(int)

setP1(Point)

setP2(Point)

2

1319.12.2006

Cost of Crosscutting Concerns

Reduced understandability Decreased adaptability Decreased reusability

Decreased maintainability

1419.12.2006

Component

Cleanly encapsulated in a generalized procedure (i.e. object, method, procedure, API)

Well-localized, and easily accessed and composed

1519.12.2006

Aspect

Properties that affect the performance or semantics of the components in systemic ways

Not cleanly encapsulated in a generalized procedure

1619.12.2006

Goal of AOP

Separate components and aspects from each other

Abstract and compose the components and aspects to produce the overall system

1719.12.2006

AOP

A promising new technology for separating crosscutting concerns that are usually hard to do in object-oriented programming

1819.12.2006

Fundamentals of AOP

Aspect as a modularization unit Three distinct development steps:

Aspectual decomposition Concern implementation Aspectual recomposition

1919.12.2006

Steps of AOP

2019.12.2006

Programming with Aspects

Writing the components Writing the aspects Weaving

2119.12.2006

Aspect Weaving

2219.12.2006

Tools for AOP

AspectJ AspectC++ AspectWerkz JAC JBoss-AOP Nanning

2319.12.2006

AspectJ

Small, well-integrated extension to JavaJava programs as input.class files compatible with any JVM as

output Free and open source AspectJ compiler

2419.12.2006

AspectJ Terminology

Join point Pointcut Advice Introduction Aspect

2519.12.2006

Join Points

Well-defined points in a program's execution

Key points in dynamic call graph

2619.12.2006

Pointcuts

A named collection of join points Designate join points

2719.12.2006

Advice

Before advice After advice Around advice

2819.12.2006

Introduction

ModifiesMembers of a classRelationship between classes

2919.12.2006

Aspect

Module for handling crosscutting concernsDefined in terms of pointcuts, advice,

and introductionReusable and inheritable

3019.12.2006

class Line { private Point _p1, _p2;

Point getP1() { return _p1; } Point getP2() { return _p2; }

void setP1(Point p1) { Tracer.traceEntry(“entry setP1”); _p1 = p1; Tracer.traceExit(“exit setP1”); }

void setP2(Point p2) { Tracer.traceEntry(“entry setP2”); _p2 = p2; Tracer.traceExit(“exit setP2”); }

class Point {

private int _x = 0, _y = 0;

int getX() { return _x; } int getY() { return _y; }

void setX(int x) { Tracer.traceEntry(“entry setX”);

_x = x; Tracer.traceExit(“exit setX”) } void setY(int y) { Tracer.traceEntry(“exit setY”);

_y = y; Tracer.traceExit(“exit setY”); }}

Example – Without AOP

Tangling Code

ScatteredConcern

class Tracer { static void traceEntry(String str) {

System.out.println(str); } static void traceExit(String str) {

System.out.println(str); }}

3119.12.2006

class Line { private Point _p1, _p2;

Point getP1() { return _p1; } Point getP2() { return _p2; }

void setP1(Point p1) { _p1 = p1; } void setP2(Point p2) { _p2 = p2; }}

class Point {

private int _x = 0, _y = 0;

int getX() { return _x; } int getY() { return _y; }

void setX(int x) { _x = x; } void setY(int y) { _y = y; }}

Example - AspectJaspect Tracing {

pointcut traced(): call(* Line.* || call(* Point.*);

before(): traced() { println(“Entering:” +

thisjopinpoint);

after(): traced() { println(“Exit:” +

thisjopinpoint);

void println(String str) {<write to appropriate stream>}

}}

pointcut

advice

aspect

Aspect is defined in a separate moduleCrosscutting is localizedNo scattering; No tanglingImproved modularity

3219.12.2006

Advantages of AOP

TractabilitySimpler cleaner codeReusabilityEasier to maintain

3319.12.2006

Disadvantages of AOP

Difficult to understand a software because of invisibly injected aspects

Fragile build problems Complicated control flow breakage Reduced quality of software if aspects are not

appropriately managed

3419.12.2006

Conclusions

Scattered crosscutting concerns over several modules causing tangling code

Explicit abstraction mechanism with AOP Increased modularity of the system

3519.12.2006

References

http://fsl.cs.uiuc.edu/images/9/9c/Kiczales97aspectoriented.pdf

http://en.wikipedia.org/wiki/Aspect-oriented_programming

http://www.developer.com/design/article.php/3308941

3619.12.2006

Thank you for your attention!

Questions?