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Re: [aspectj-users] Bug Collection + declare parents?
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Hi Luca.
I am nowhere near a PC now, so I cannot run/test your code, but from what I see I am really surprised you do not get more errors earlier in the process because it just does not make sense to ITD-declare a class to implement an interface without also specifiying an actual implementation. I wonder why it even compiles. Don't you see any compilation errors? Maybe the class file just (partly) works by chance because Ajc has produces halfway usable bytecode before terminating.
Probably you will get more qualified feedback from Andy Clement or even from me when I have time to actually switch on my home office PC (which can be days from now). My hint is just quick and first-aidish.
Regards
--
Alexander Kriegisch
http://scrum-master.de
> Am 04.03.2015 um 17:05 schrieb Savoja Luca <luca.savoja@xxxxxxxxxxxxxxxxx>:
>
> Hello everyone,
>
> I found a situation where i get a ClassCastException that might not be thrown.
> With declare parents I force a class to implement an interface, in an aspect i put an object of this class in a collection of the interface's type. And everythig works fine thus far.
> Then when i extract the object from the collection i get a ClassCastException.
>
>
> Here's an example that illustrates what i'm describing you.
>
> I've a simple interface:
>
> public interface MyInterface {
> void myMethod();
> }
>
> and a class that i force to implement it by declare parents.
>
> public class ClassImplementingInterf {
> //if the the interface methods are present in the implementing class there's no cast error
> /*
> public void myMethod(){ //NB: commented, not present.
> System.out.println("myMethod");
> }
> */
> }
>
> then I have an abstract aspect:
>
> public abstract aspect MyAspect {
> private ArrayList<MyInterface> x = new ArrayList<MyInterface>();
>
> abstract pointcut interfacemethod();
> abstract pointcut mypointcut();
>
> void around(): mypointcut(){
> ClassImplementingInterf obj = new ClassImplementingInterf();
>
> x.add(obj); //working
> MyInterface var = (MyInterface) obj; //working
> ClassImplementingInterf fromListWithCast = (ClassImplementingInterf) x.get(0); //working
>
> System.out.println("Just before MyInterface fromLst = x.get(0)");
> MyInterface fromLst = x.get(0); //ClassCastException
>
> System.out.println("**** intercepted OtherClass.method ***** "); //not reached!
> }
>
> void around(): interfacemethod(){
> System.out.println("**** intercepted interface method **** ");
> }
> }
>
> and it's concrete aspect:
>
> public aspect ConcreteAspect extends MyAspect {
> declare parents: ClassImplementingInterf implements MyInterface;
>
> pointcut mypointcut(): call(public void OtherClass.method(int));
> pointcut interfacemethod(): call(void *.*.myMethod());
> }
>
> and an other class (useless, i use it only for intercept the method)
> public class OtherClass {
> public void method(int n){
> System.out.println(n*2);
> }
> }
>
> The main class is:
> public class ClassMain {
> public static void main(String[] args) {
> OtherClass o = new OtherClass();
>
> MyInterface ci = new ClassImplementingInterf();
> ci.myMethod(); //this works!! the class can act like it has the interface!
>
> o.method(15);
> }
> }
>
>
> As you can see i can put an ClassImplementingInterf instance in a MyInterface variable or collection, and I can also cast it to MyInterface.
> But when extracting it from a collection it doesn't work.
>
> I think there's some kind of reflective controls when extracting an element from a collection that fails when i do it.
> Sure enough if i add to ClassImplementingInterf a method that has the same signature of the interface the ClassCastException disappears and everything works fine.
>
> I've attached to this message a .rar package that contains my code.
>
> Best Regards,
> --
> Luca Savoja.
> <provaBug.rar>
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