1. For John

2. DAJ (temporary name for AspectJ with traversals)
planned to be added to AspectJ
provides an efficient implementation of traversals using the AP library
we have also added traversals to Java but implementation is very slow (using reflection)
AspectJ + traversals > Java + traversals because AspectJ > Java

3. Adding Demeter Traversals to AspectJ
Because the AspectJ join point model is a generalization of Demeter’s join point model, we can use the AspectJ pointcuts to express the traversal pointcuts for visitors.
declare ClassGraph
declare TraversalGraph
declare Behavior

4. Traversal(t) pointcut
picks out all join points between the start and the end of the traversal that are needed for the traversal only, i.e. the node visits and the edge visits.

5. Traversal Syntax Example
aspect MyTraversal {
ClassGraph defaultCG = new ClassGraph();
ClassGraph cg1 = new ClassGraph(defaultCG,
“from CompoundFile to * bypassing ->*,tail,*”);
declare traversal t1: “from CompoundFile to SimpleFile”;
declare traversal t2(cg1): “from CompoundFile to *”; }

6. Traversal Syntax Example
aspect MyTraversal {
declare visitors : VisitorInterface1;
ClassGraph defaultCG = new ClassGraph();
ClassGraph cg1 = new ClassGraph(defaultCG,
“from CompoundFile to * bypassing ->*,tail,*”);
declare traversal t1(defaultCG):
“from CompoundFile to SimpleFile”;
declare traversal t2(cg1, VisitorInterface1):
“from CompoundFile to *”; }

7. Generate pointcuts / advice
interface VisitorInterface1 {
void before(Object host);
void after(B host);
void after(C source, D target);
void around(A host);
void start();
void finish(); }

8. M1: Equation System used = from EquationSystem
via -> *,rhs,* to Variable
M1: Equation System
EquationSystem
equations
Equation_List
Ident *
lhs
Equation
Variable
Numerical
rhs
Simple
args
Expression
Expression_List S T * op
Add
Compound D B

9. Motivation for edge advice
before_rhs < before !
Motivation for edge advice
for each used variable v print the largest expression that contains v
class LargestVisitor { Expression exp;
void before_rhs(Object s, Expression t){
exp = t; };
void before(Variable v) {
System.out.println(exp, v) }
from EquationSystem via -> *,rhs,* to Variable

10. Motivation for edge advice
from EquationSystem to Variable
around < before !
Motivation for edge advice
class MarkVariableVisitor { boolean through_lhs; …
void before(Variable v) {
if (through_lhs) { … } else
if (through_rhs) { … } };
void around_lhs(Subtraversal t){
through_lhs = true;
t.proceed();
through_lhs = false;
}; … }
for each variable print whether
it is used or defined

11. Self-Contained Example
Java classes
Traversal file
Use traversal defined

12. Basket Example Basket f p Pencil Fruit Orange w c Weight Color int i s
String

13. BasketMain.java class Weight{ class Basket { Weight(int _i) { i = _i;}
int get_i() { return i; } }
class Pencil {}
class Color {
Color(String _s) { s = _s;}
String s;
class Basket {
Basket(Fruit _f, Pencil _p) { f = _f; p = _p; }
Fruit f;
Pencil p; }
class Fruit {
Fruit(Weight _w) { w = _w; }
Weight w;
class Orange extends Fruit {
Orange(Color _c) { super(null); c=_c;}
Orange(Color _c, Weight _w) { super(_w); c = _c;}
Color c;

14. BasketMain.java class BasketMain {
static public void main(String args[]) throws Exception {
Basket b = new Basket(
new Orange(
new Color("orange"),
new Weight(5)),
new Pencil());
int totalWeight = b.totalWeight();
System.out.println("Total weight of basket = " +
totalWeight); }}

15. Traversals Count the total weight within the basket
Traversal Strategy: “From Basket to Weight”
Visitor: Add up all the values within Weight

16. Basket Example Traversal Graphf p
Pencil
Fruit
Orange w c
Weight
Color
int i s
String

17. Two versions define visitor using AspectJ pointcuts and advice
Java visitor class complete with initialization, finalization and return value processing

18. BasketTraversal.trv // traversals for basket aspect BasketTraversal {
declare ClassGraph default;
declare ClassGraph myClassGraph : default,
"from Basket to * bypassing {->*,*,java.lang.String }");
declare traversal t2(myClassGraph) : "from Basket to Weight";
declare TraversalGraph t2 : myClassGraph, "from Basket to Weight"; }

19. generated: BasketTraversal.java
public aspect BasketTraversal {
// traversal t2 : {source: Basket -> target: Weight} with { }
public void Basket.t2(){
if (f != null) t2_crossing_f(); }
public void Basket.t2_crossing_f() { f.t2();}
public void Fruit.t2(){
if (w != null) t2_crossing_w();
public void Fruit.t2_crossing_w() { w.t2();}
public void Weight.t2(){
public void Orange.t2(){
super.t2(); }
pointcut pointcut_t2() : call(public void t2*());
before () : pointcut_t2 () {
System.out.println(thisJoinPoint);
} // BasketTraversal
for testing
traversal code

20. BasketMainCount.java
// the aspect for counting the total weight of the basket
aspect BasketMainCount {
static int returnVal;
int Basket.totalWeight() {
returnVal = 0;
t2();
return returnVal; }
pointcut t2WeightPC(Weight weight) : call(* *t2*()) && target(weight);
before(Weight weight) : t2WeightPC(weight) {
returnVal += weight.get_i();

21. BasketTraversal.trv “visitor in Java” version // traversals for basket
aspect BasketTraversal {
declare ClassGraph default;
declare ClassGraph myClassGraph : default,
"from Basket to * bypassing {->*,*,java.lang.String }");
declare traversal Integer t2(myClassGraph, SumVis) :
"from Basket to Weight"; }

22. BasketTraversal.trv !!!!!!!!!!!!!!! Better “visitor in Java” version
// traversals for basket
aspect BasketTraversal {
declare ClassGraph default;
declare ClassGraph myClassGraph : default,
"from Basket to * bypassing {->*,*,java.lang.String }");
declare TraversalGraph tg : myClassGraph, “from A to B”; // tg()
declare Behavior void b1 : tg, Vis; //b1()
declare Behavior Integer summing : myCg, “from A to B”, Vis; //b2()
declare traversal Integer t2(myClassGraph, SumVis) :
"from Basket to Weight"; }

23. BasketMainCount.java
// the aspect for counting the total weight of the basket
aspect BasketMainCount {
int Basket.totalWeight() {
Integer retVal = summing();
return retVal.intValue(); }
class SumVis {
int retVal = 0;
void before (Weight w) {retVal += weight.get_i();}
Object returnVal() {return new Integer(retVal);}

24. Compilation Process Detail
Traversal
Files
Stub
Java
Files
AspectJ
Compiler
CreateClassGraph.java
DAJ
JVM
AspectJ
Files
AspectJ
Compiler
Class Files
Traversal
Implementation
and User Class Files
Traversal
Implementation
Java Files