What is AOP?

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What is AOP?
Once More Around the Wheel

• Gregor Kiczales
• AspectMentor.com and
• University of British Columbia

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• Consider developinga simple drawing application
  (JHotDraw)

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objects are intuitive

• Intuitively thinking of objects?
• Points, Lines
• Drawing surfaces
• GUI Widgets

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objects are not intuitive
objects are intuitive

• In 1969 most programmers would have used
• this has poor design and code modularity!

2 4


22 12
65 93
43 29
86 65






6 7 5 8


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not intuitive

• OOP invented in 1961
• about same time as structured programming
• term object-oriented programming in 1967
• to make simulation code look like the model

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• What is OOP?
• a way of thinking
• objects, classification hierarchies
• supporting mechanisms
• classes, encapsulation, polymorphism
• allows us to
• make code look like the design
• improves design and code modularity
• many possible implementations
• style, library, ad-hoc PL extension, integrated
  in PL

many other benefits build on these
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OOP
MVC
Observer Pattern
fair design modularitybut poor code modularity
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OOP
MVC
Observer Pattern

• Meanwhile back at the ranch
• starting in early 80s (perhaps earlier)
• others began work on
• crosscutting structure
• mechanisms
• behavioral reflection, metaobject
  protocols,subject-oriented programming
• aspect-oriented programming term in 1997

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aspect ObserverPattern private Display
Shape.display pointcut change()
call(void figures.Point.setX(int))
call(void Point.setY(int)) call(void
Line.setP1(Point)) call(void
Line.setP2(Point)) call(void
Shape.moveBy(int, int)) after(Shape s)
returning change()
target(s) s.display.refresh()
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ObserverPattern
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aspect ObserverPattern private Display
Shape.display pointcut change()
call(void Shape.moveBy(int, int))
call(void Shape.set(..)) after(Shape s)
returning change()
target(s) s.display.refresh()
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ObserverPattern
well-definedcrosscutting structure
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Ask yourselfcould you name asingle class
ObserverPattern ?
aspect ObserverPattern private Display
Shape.display pointcut change()
call(void Shape.moveBy(int, int))
call(void Shape.set(..)) after(Shape s)
returning change()
target(s) s.display.refresh()
1
ObserverPattern
well-definedcrosscutting structure
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• What is AOP?
• a way of thinking
• aspects, crosscutting structure
• supporting mechanisms
• join points, pointcuts, advice
• allows us to
• make code look like the design
• improve design and code modularity
• many possible implementations
• style, library, ad-hoc PL extension, integrated
  in PL

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• Other Aspects
• design patterns Google AOP design pattern
• Swing thread safety AspectJ in Action
• policy enforcement
• authentication, synchronization, architecture
• transaction management
• debugging support
• logging (of course)
• and many application-specific aspects

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• IBM reports
• implementation of platform policies
• 15-30 quality improvements
• significant productivity gains
• improvements in modularity of complex software
• new business opportunities

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• Issues
• good vs. bad uses
• can overuse/misuse any mechanism
• we have learned a lot, we need to learn more
• over hype, bad pedagogy
• each new wave of adoption brings new zealots /
  critics
• some old lessons need to be rediscovered
• tools
• quality, support
• training, organization structure
• whats the business value?

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• Issue Proper Style
• mechanisms can be misused
• too many or wrong procedures
• too many or wrong classes
• too much or wrong overriding
• too many or wrong aspects, advice, introductions
• we already know a lot
• 15 rule, well-defined crosscutting, tool support
• we have a lot to learn
• interaction w/ JSR-175 more semantic pointcuts
• scaling

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• Issue Implementation Quality
• implementations vary gt 10x in performance!
• range of existing strategies
• VM-based implementation just now starting
• limited existing benchmarks
• but this is getting better fast

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• Issue Over-stated claims, bad pedagogy
• each wave of interest / adoption
• new proponents and critics
• have different priorities
• but must re-learn old lessons
• new generations of proponents
• can be too optimistic
• new generations of teachers
• can miss critical insights
• new generation of critics
• can miss previously discussed issues

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• Question for panelHow can Java Platform remain
  1 for AOP?
• what are the next steps?
• how does really new technology get in?
• what are the technical issues?
• how can AOP get proven enough
• what are market issues?
• is AOP disruptive technology for J2EE?
• where does it produce significant value?
• what will Redmond do?