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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

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

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.

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 *”; }

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 *”; }

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(); }

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

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

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

Self-Contained Example Java classes Traversal file Use traversal defined

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

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;

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); }}

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

Basket Example Traversal Graph f p Pencil Fruit Orange w c Weight Color int i s String

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

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"; }

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

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();

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"; }

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"; }

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);}

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