Description Laurie Hendren 2004-06-17 04:06:53 EDT

In ajc a use of thisJoinPoint corresponds to an object of type JoinPoint, where
a JoinPoint object has four components, which can be retrieved using
accessor methods.

  this                   getThis()
  target                 getTarget()
  args                   getArgs()
  staticJoinPoint        getStaticPart()

In the case of args, the object returned is an Object array.  This means
that an advice decl can overwrite the args,  and then another advice which
shares the same JoinPoint will see the changed args.   Here is a
small example.  In this aspect the
before advice changes arg[0] to always be "Laurie" and then the after
advice will always say that "Laurie won a million pounds".

Is this the behaviour that is intended?   I would have thought that the
interface to args[] should be such that the values can only be read.  Otherwise
very strange interactions between advice decls could occur.

---------------------------------------------------------------------

public class Main {

  public static Main v = new Main();

  void lottery ( String arg )
    { System.out.println("The arg in lottery is " + arg);
    }

  public static void main (String args[])
    { v.lottery("Oege");
      v.lottery("Ganesh");
    }

}

---------------------------------------------------------------------

public aspect Aspect {

  // This pair of advice decls demonstrates that an advice can change to
  //   the args of a join point.

  before () : call(* lottery(java.lang.String)) && !within(Aspect)
    { System.out.println("BEFORE " + thisJoinPoint +
                         " at " + thisJoinPointStaticPart.getSourceLocation());
      Object args[] = thisJoinPoint.getArgs();
      System.out.println("arg[0] is " + args[0]);
      args[0] = "Laurie";
      System.out.println("... now it is " + thisJoinPoint.getArgs()[0]);
    }


  after ()  : call(* lottery(java.lang.String)) && !within(Aspect)
    { System.out.println("AFTER " + thisJoinPoint +
                         " at " + thisJoinPointStaticPart.getSourceLocation());
      if (thisJoinPoint.getArgs()[0].equals("Laurie"))
        System.out.println("Laurie wins 1 million pounds!");
    }

}