An Aspect-Aware Outline Viewer
Michihiro Horie and Shigeru Chiba
Tokyo Institute of Technology, Japan
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Our purpose

Problem: difficulty to understand relationships
between programs and aspects



Obliviousness: aspects and classes separately specified
Must understand whole system to understand one class
Solution:



Overcome program and aspects separation in visualization
But keep obliviousness in the code
To ensure code/visualization consistency: need for
automatic tools
2
AJDT

AJDT shows


For AJDT,



Join points selected by pointcuts
AOP is an event-based programming.
AJDT shows the locations of events.
No modular reasoning


Broken encapsulation
Developers must see the internal implementation of
a class to understand the program behavior.
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Our solution: AspectScope


Overcomes the limitations of AJDT
Preserves modular reasoning


More abstract reasoning
Helps better understand programs
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AspectScope

An outline viewer of a class


Eclipse plug-in for AspectJ
It shows the outline of a class woven with an aspect


Modules = classes, methods and fields
Generates javadoc comments for modules

outline
Document how and when aspects extend their behavior
ここに AspectScope の図
javadoc
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Modular reasoning

AspectScope enables modular reasoning




No show of source code (the implementation of
methods)
Encapsulation is preserved.
Still shows enough information to help understanding
In AspectScope, an aspect is an extension to a class.

AspectScope shows an extension by an aspect as part of
“the specification of a module interface”.
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Modular reasoning

Concrete benefit:


Abstracts the differences between some kinds of
pointcuts, to simplify visualization
Concrete example: unified representation of
“execution pointcuts” and “call pointcuts”
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Execution pointcut

visualized by AspectScope
AspectScope indicates…

an advice extends the behavior of a callee method.
after(): execution(void Point.setX(int)) {
Display.update();
}
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Call pointcut

(also get & set)
AJDT indicates..

An advice intercepts a call in a caller method.
after(): call(void Point.setX(int)) {
Display.update();
}
Caller class
AJDT Editor
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Call pointcut

(also get & set)
Unlike AJDT, AspectScope indicates...

An advice extends the behavior of a callee method.
after(): call(void Point.setX(int)) {
Display.update();
}
AspectScope
Callee
class
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Aspects as conditional extensions

In AspectScope, aspects are module extensions


But can be conditional: within and cflow pointcuts
Extension only if a caller satisfies a condition
after(): call(void Point.setX(int)) && within(Line) {
Display.update();
}
Conditional
extension
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javadoc comments

Automatically generated or gathered from
from source code of methods and advices
From the implementation
of setX()
From the pointcut
definition
From the advice
definition
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Explaining pointcuts

Interprets all AspectJ’s pointcuts into “developer
English”
pointcut move() :
call(void Shape+.set*(int))
|| call(void Shape+.moveBy(..));
void setX(int)
Wild cards *, + , and .. are
expanded to concrete name.
after(): move() && within(Line) {
Display.update();
}
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Concrete example 1: Observer aspect
 An advice is executed when a setter method is
called.
Display
Shape
1
*
…
…
The advice is not executed
when setX() is called
within setP1() in Line.
update()
…
Line
Point
setP1(Point p1)
setP2(Point P2)
…
setX(int x)
setY(int y)
…
pointcut change() : call(void Shape+.set*(..));
after(): change() && !cflowbelow(change()) {
Display.update();
}
Rectangle
…
…
…
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AspectScope vs. AJDT
AspectScope
AJDT Editor
AJDT shows join point
shadow at a caller side.
AspectScope shows how
setP1() is extended for notifying
an observer of updates.
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Concrete example 2: Logging aspect

Print a log message just before a method in
Canvas calls draw() in Graphics.
class Canvas {
Image image;
:
void paint(Graphics g) {
:
g.draw(image);
:
}
:
}
aspect LoggingAspect {
before(): call(* Graphics.draw(..))
&& within(Canvas) {
System.out.println(“log”);
}
}
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AspectScope vs. AJDT
AspectScope
AJDT Editor
AJDT shows a caller-side
expression.
AspectScope shows the
extension to a callee-side
method.
before() : call(void Graphics.draw(Image))
&& within(Canvas) {
System.out.println(…);
}
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Related Work

Aspect-Aware Interface [Kiczales et al. ‘05]

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It shares basic ideas with AspectScope.
Conceptual framework for modular reasoning.

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This paper does not mention call, get, and set pointcuts.
No javadoc comments.
Not a practical development tool, unlike AspectScope.
Classbox/J [Bergel et al. ‘05]


Similar to the interpretation of aspects by AspectScope.
Enables an extension only effective to a particular module.
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Conclusion

AspectScope:
A programming tool for AspectJ


An outline viewer of a class
It shows the outline of a class woven with an aspect




Declared methods and fields
javadoc comments for the methods and fields
How and when the aspect extends their behavior
It enables modular reasoning
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Intertype declaration

AspectScope indicates appended methods and fields.
public aspect UpdateSignaling {
Point Point.getLocation() { … }
:
}
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