Annotation on lambda formal parameter?

Brian Goetz brian.goetz at
Thu Dec 13 13:32:30 PST 2012

I think we did, but the JSR-308 EG is asking us for that opinion.

While one might say "sure, annotations should be allowed everywhere, 
what's the harm", the reality is that it is not going to be easy for 
tools to *find* annotations on lambda formal parameters, since 
reflection only goes down to the method level and not the AST level.

Also, this query is not about type annotations on the types of explicit 
lambda parameters; it's about annotations on the parameters themselves. 
  While containers use parmeter annotations for things like injection, I 
am having a hard time seeing a use case that is both sensible and 

On 12/13/2012 4:18 PM, Dan Smith wrote:
> Didn't we already address this with "Modifiers on Inferred-Type Lambda Parameters", which we rejected (in email "Some rejected ideas" 5 Jul 2012, then in the August meeting)?  Or am I misunderstanding the question?
> —Dan
> On Dec 11, 2012, at 9:35 PM, Brian Goetz <brian.goetz at> wrote:
>> Received from the -comments list.  Note that this is largely a query of "what does the Lambda EG think the JSR-308 EG should do".
>> -------- Original Message --------
>> Subject: Annotation on lambda formal parameter?
>> Date: Tue, 11 Dec 2012 16:27:23 -0800
>> From: Alex Buckley <alex.buckley at>
>> Organization: Oracle Corporation
>> To: lambda-spec-comments at
>> CC: Michael Ernst <mernst at>
>> Lambda EG,
>> JSR 308 "Annotations on Java Types" will allow annotations on the
>> manifest type of a lambda expression's formal parameter, and on the type
>> and/or type argument in a method/constructor reference expression.
>> Is there any interest in having 308 allow an annotation on a lambda
>> formal parameter itself? That is, on the declaration of the parameter,
>> rather than its type. A declaration annotation is conceptually valid
>> even if the parameter declaration has no manifest type on which to write
>> a type annotation.
>> This is somewhat in scope for 308 because it already allows annotations
>> on declarations of type parameters (filling a hole from Java SE 5.0) and
>> it has the sub-method-level class file attributes needed to store
>> annotations on declarations of individual lambda parameters.
>> Alex

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