1. Adaptive Programming in JAsCo
Wim Vanderperren
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2. Adaptive Programming (1)
Law of Demeter: a method should talk only to its
friends:
arguments and part objects (computed or stored)
and newly created objects
Example:
class Test {
Test2 test2;
public void do() {
test2.getTest3().start(5); }
NOT GOOD
JAsCoAP
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3. Adaptive Programming (1)
Law of Demeter: a method should talk only to its
friends:
arguments and part objects (computed or stored)
and newly created objects
Better Example:
class Test2 {
Test3 test3;
public void do(int i){
test3.start(i); }
class Test {
Test2 test2;
public void do() {
test2.do(5); }
BUT: “do” logic is spread over several classes now
JAsCoAP
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4. Adaptive Programming (2)
Law of Demeter: a method should talk only to its
friends:
arguments and part objects (computed or stored)
and newly created objects
Dilemma:
Crosscutting concerns (if follow) or
Unmaintainable code (if not follow)
AP is the solution to this dilemma
JAsCoAP
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5. Adaptive Programming (3)?
 Save contents of DataStores to file …
ClassA DS
Visitor
from ClassA to DataStore
AP Option
Class SaveVisitor {
saveA(ClassA a);
saveB(ClassB b); … }
Class Save {
save(ClassA a) {
a.B.C.DataStore;
a.F.E.Datastore; } DS
Visitor
Option 1
Option 2
Crosscutting Concerns
Violates Law of Demeter
ClassB
ClassF
Data-
Store
ClassC
ClassD
ClassE
Data-
Store
JAsCoAP
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6. Adaptive Programming (4)
Traversal Strategy:
Specifies the abstract traversal that has to be followed.
Example: From Test to Test3
Adaptive Visitor:
Implements the behavior itself
Visits the concrete traversal as specified by the abstract traversal strategy.
JAsCoAP
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7. Structure-shy visitors Robustness wrt evolution of base program
Advantages of AP
Structure-shy visitors
Robustness wrt evolution of base program
Separation of concerns
Complementary to all OO based approaches, even AOP
Optimal visiting process
JAsCoAP
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8. Why combine AP & JAsCo?
class DataStorePersistence extends Visitor {
public void before(DataStore store) {
if(changedPV(store)) {
Writer writer = …
writer.writeObject(store.getData()); }
public boolean changedPV(DataStore s) {
\\ true if changed since last visit
What if we want to deploy AP visitors in a component- based context …
AP visitors are already structure-shy.
But, still refer to specific types and APIs!
void backup(ClassA a) {
ClassGraph cg = new ClassGraph(“a”);
Strategy sg = new
Strategy(“from ClassA to DataStore”);
TraversalGraph tg = new
TraversalGraph(sg, cg);
tg.traverse(a, new DataStorePersistence()); }
JAsCoAP
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9. Represent Adaptive Visitors as regular aspect beans
JAsCo AP: the idea
Represent Adaptive Visitors as regular aspect beans
Introduce a new kind of connector, called “traversal connector”, for instantiating an aspect bean as an adaptive visitor on a certain traversal strategy.
JAsCoAP
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10. Brief JAsCo Intro call, cflow, withincode, target
class DataPersistence {
hook Backup {
Backup(triggeringmethod(..args)) {
execution(triggeringmethod); }
isApplicable() {
// true when changed since last visit }
before() {
Writer writer = …
writer.writeObject(getDataMethod()); }
refinable Object getDataMethod();
Deploy
Abstract method parameter
call, cflow, withincode, target
connector PersistenceConnector {
DataPersistence.Backup hook = new
DataPersistence.Backup(
* DataStore.set*(*)); }
Abstract pointcut
Triggering condition
around, around throwing, around returning, after, after throwing, after returning
refining DataPersistence.Backup
for DataStore {
public Object getDataMethod() {
DataStore d = thisJoinPointObject;
return d.getData(); }
JAsCoAP
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11. Aspect Beans as AP visitors
 An dedicated connector: traversal connector.
from … bypassing …
from … via … …
Traversal Strategy
traversalconnector BackupTraversal(“from ClassA to *”) {
DataPersistence.Backup hook = new
DataPersistence.Backup(visiting DataStore);
hook.before(); }
Object type to visit
Advice to invoke & Precedence
visiting *
visiting Data* …
public void backup(ClassA a) {
BackupTraversal myBackup =
BackupTraversal.getInstance();
myBackup.traverse(a); }
hook1.before();
hook2.before();
hook2.after();
hook1.after();
Explicit invocation
JAsCoAP
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12. JAsCoAP: Precedence Strategies
traversalconnector BackupTraversal("from system.Root to *") {
DataPersistenceAspectBean.Backup backup = new
DataPersistenceAspectBean.Backup(visiting DataStore) {
public void getDataMethod(Object context) {
DataStore store = (DataStore) context;
return store.getData(); } };
Logger.FileLogger logger = new
Logger.FileLogger(visiting *);
logger.before();
backup.before();
JAsCoAP
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13. Combining multiple AP visitors
 How to combine the behavior of multiple AP visitors?
Only execute if Save Visitor executed
ClassA
Save
Visitor
Save
Visitor
Log
Visitor
ClassB
ClassF
from ClassA to *
Data-
Store
ClassC
ClassD
ClassE
Data-
Store
But keep AP visitor implementation independent …
JAsCoAP
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14. JAsCoAP: Combination Strategies
public class TwinCombinationStrategy
implements CombinationStrategy {
private Object hookA,hookB;
TwinCombinationStrategy(Object a, Object b) {
this.hookA=a;
this.hookB=b; }
HookList verifyCombinations(HookList list) {
if(!list.contains(hookA))
list.remove(hookB);
return list;
JAsCoAP
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15. JAsCoAP: Combination Strategies (2)
traversalconnector BackupTraversal("from system.Root to *") {
DataPersistenceAspectBean.Backup backup = new
DataPersistenceAspectBean.Backup(visiting DataStore) {
public void getDataMethod(Object context) {
DataStore store = (DataStore) context;
return store.getData(); } };
Logger.FileLogger logger = new
Logger.FileLogger(visiting *);
logger.before();
backup.before();
TwinCombinationStrategy twin = new
TwinCombinationStrategy(backup,logger);
addCombinationStrategy( twin);
JAsCoAP
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16. JAsCoAP: Advanced Traversal Strategies
Bypassing:
“from A bypassing C to B”
via :
“from A via C to B”
->Start,field,End :
“from A via ->C,f,* to B” x A C f D B … E E g g
JAsCoAP
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17. Structure-shy visitors Robustness wrt evolution of base program
Advantages of JAsCo AP
Structure-shy visitors
Robustness wrt evolution of base program
Separation of concerns
Increases Aspect Bean reusability
Completely Abstract Adaptive Visitors represented as Aspect Beans
Managing combined visiting behavior by Precedence&Combination strategies
JAsCoAP
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18. Exercises
JAsCoAP
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