1 An Aspect-Aware Outline Viewer Michihiro Horie and Shigeru Chiba Tokyo Institute of Technology, Japan

2 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

3 AJDT AJDT shows  Join points selected by pointcuts For AJDT,  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.

4 Our solution: AspectScope Overcomes the limitations of AJDT Preserves modular reasoning  More abstract reasoning  Helps better understand programs

5 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  Document how and when aspects extend their behavior ここに AspectScope の図 outline javadoc

6 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, a n aspect is an extension to a class.  AspectScope shows an extension by an aspect as part of “the specification of a module interface”.

7 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”

8 Execution pointcut visualized by AspectScope  AspectScope indicates… an advice extends the behavior of a callee method. after(): execution(void Point.setX(int)) { Display.update(); }

9 Call pointcut(also get & set) AJDT indicates..  An advice intercepts a call in a caller method. AJDT Editor after(): call(void Point.setX(int)) { Display.update(); } Caller class

10 Call pointcut(also get & set) Unlike AJDT, AspectScope indicates...  An advice extends the behavior of a callee method. AspectScope after(): call(void Point.setX(int)) { Display.update(); } Callee class

11 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

12 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

13 Explaining pointcuts Interprets all AspectJ’s pointcuts into “developer English” pointcut move() : call(void Shape+.set*(int)) || call(void Shape+.moveBy(..)); after(): move() && within(Line) { Display.update(); } Wild cards *, +, and.. are expanded to concrete name. void setX(int)

14 Concrete example 1: Observer aspect An advice is executed when a setter method is called. Shape … Point setX(int x) setY(int y) … Line setP1(Point p1) setP2(Point P2) … Rectangle … Display update() … * 1 pointcut change() : call(void Shape+.set*(..)); after(): change() && !cflowbelow(change()) { Display.update(); } The advice is not executed when setX() is called within setP1() in Line.

15 AspectScope vs. AJDT AJDT Editor AJDT shows join point shadow at a caller side. AspectScope AspectScope shows how setP1() is extended for notifying an observer of updates.

16 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”); }

17 AspectScope vs. AJDT AJDT Editor AspectScope AspectScope shows the extension to a callee-side method. AJDT shows a caller-side expression. before() : call(void Graphics.draw(Image)) && within(Canvas) { System.out.println(…); }

18 Related Work Aspect-Aware Interface [Kiczales et al. ‘05]  It shares basic ideas with AspectScope.  Conceptual framework for modular reasoning. 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.

19 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

20 public aspect UpdateSignaling { Point Point.getLocation() { … } : } Intertype declaration  AspectScope indicates appended methods and fields.