AspectOriented Programming:

1

• Aspect-Oriented Programming
• An Overview
• Brandon Wirick
• Feb. 2005

2
Layers of Abstraction

• Machine code to assembly
• Assembly to procedural languages
• Procedural to object-oriented
• Group similar compile-time functional units
• Object- to aspect-oriented
• Group similar run-time functional units

3
Terminology

• AOP
• AOSD
• Concerns
• common
• crosscutting
• Aspect
• AspectJ

• Join-point
• Poincut
• Weaving
• compile-time
• run-time
• Loop fusion
• Tangling

4
AspectJ

• Java with aspects
• Aspects are singleton classes
• Group join-points into pointcuts
• Define behavior before, after, or around
  pointcuts
• Specify contract enforcements
• Can contain members, like classes
• Definitely most prominent language

5
AspectJ Example

• public aspect NoNulls
• public static interface Addable
• public boolean add(Object o)
• pointcut add(Object o)
• call(boolean Addable.add(Object))
  args(o)
• boolean around(Object o) add(o)
• boolean success (o ! null)
• success proceed(o)
• return success
• class NoNullsVector extends Vector implements
  NoNulls.Addable
• class NoNullsArrayList extends ArrayList
  implements NoNulls.Addable

6
Kiczales et al, 1997

• Noted certain problems could have implementations
  that are either
• Efficient, but hard to understand
• Inefficient, but easy to understand
• Efficient and easy to understand, but only with
  AOP!
• Reduction in bloat due to tangling

7
Design Pattern Libraries

• public abstract aspect ObserverProtocol
• protected interface Subject
• protected interface Observer
• ...
• protected abstract pointcut
• subjectChange(Subject s)
• ...
• public aspect ColorObserver extends
  ObserverProtocol
• declare parents Point implements Subject
• declare parents Screen implements Observer
• ...

8
Not for Dumb Programmers

• Easy to do wrong
• Complicated to understand
• Controversial
• Not so much anymore
• Arguments against AOP pretty weak
• Some unpredictable behavior?