JEP 120: Repeating Annotations

[Joseph Darcy]

On 1/6/2012 9:48 AM, Jesse Glick wrote:
> On 01/05/2012 06:32 PM, Joe Darcy wrote:
>> other consumers of class files don't have to have extensive 
>> modifications.
>
> If there are other class file parsers which assume (contrary to the 
> current JVM spec!) that only one annotation of a given type is present 
> on a given element, they would need to be fixed - e.g. using a list or 
> multimap rather than a map, or simply ignoring second and subsequent 
> occurrences if irrelevant for their use case. This does not feel like 
> "extensive modifications", especially if compared to other likely 
> class file changes such as for lambdas, but it is true that it is a 
> change when compared to JDK 7 (at least when restricted to class files 
> produced by javac).
>
>> any solution to repeating annotations that did not acknowledge and 
>> leverage this situation is unlikely to have speedy adoption.
>
> Well assuming that the code which reads the annotation 
> (elt.getAnnotation(Thing.class)) is in the same overall source project 
> as the definition of the annotation itself (Thing.java), which is 
> typical, and assuming that this feature is targeted for JDK 8, there 
> are several cases:

This will not be the typically arrangement for, say, enterprise apps 
using Java EE standard annotations, many of which use the 
container-annotation work around to get the effect of repeating annotations.

I do not think it is prudent to require that code that reads and 
interprets those annotations to be updated to a new idiom before the 
improved syntax can be used in clients.

-Joe