JDK 8 RFR for JDK-7185456 : (ann) Optimize Annotation handling in java/sun.reflect.* code for small number of annotationsC

[Joel Borggrén-Franck]

On 03/27/2013 03:00 PM, Peter Levart wrote:
> On 03/27/2013 02:00 PM, Joel Borggrén-Franck wrote:
>> Hi Peter,
>>
>> On 03/27/2013 01:31 PM, Peter Levart wrote:
>>
>>> I also don't know
>>> whether having LinkedHashMap instead of plain HashMap is necessary, since it
>>> is initialized with defaults from plain HashMap (which is hashCode %
>>> capacity ordered) and only some of defaults are overridden in parsing loop
>>> in general. For example, having this annotation:
>>>
>>> @interface Ann {
>>>      String one();
>>>      String two() default "2";
>>> }
>>>
>>> and usage:
>>>
>>> @Ann(one = "1")
>>>
>>> ...toString will print: @Ann(two = "2", one = "1")
>>>
>>
>> While there perhaps is no natural ordering between the sets of default
>> elements and non-default elements you probably want an order following
>> source as closely as possible among the non-default elements.
>
> What is the order of elements in java class file (the bytes that the parser
> interprets)? Is it taken from the declaration of annotation (the order of
> methods in annotation interface) or from the use-site of the annotation? Is
> this specified?
>

In general javac tries to keep source order on "things" when emitting to a 
class file. I believe this is often specified as natural order, but don't 
trust me on this. In this specific case I would guess element use order from 
the annotatio instance.

In the following small example I note that 'b' comes before 'a' in the const 
pool but the RuntimeInvisibleAnnotations 'a' is before 'b'. I don't think 
this is a coincidence.

anno-order$ cat T.java
@T(a="XYZ", b="DEF")
public @interface T {
     String b();
     String a();
}

anno-order$ javap -v T.class
Classfile /localhome/src/test/anno-order/T.class
   Last modified Mar 27, 2013; size 239 bytes
   MD5 checksum e1c7d8d76842d219c9853463af37830a
   Compiled from "T.java"
public interface T extends java.lang.annotation.Annotation
   SourceFile: "T.java"
   RuntimeInvisibleAnnotations:
     0: #10(#6=s#11,#4=s#12)
   minor version: 0
   major version: 52
   flags: ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT, ACC_ANNOTATION
Constant pool:
    #1 = Class              #13            //  T
    #2 = Class              #14            //  java/lang/Object
    #3 = Class              #15            //  java/lang/annotation/Annotation
    #4 = Utf8               b
    #5 = Utf8               ()Ljava/lang/String;
    #6 = Utf8               a
    #7 = Utf8               SourceFile
    #8 = Utf8               T.java
    #9 = Utf8               RuntimeInvisibleAnnotations
   #10 = Utf8               LT;
   #11 = Utf8               XYZ
   #12 = Utf8               DEF
   #13 = Utf8               T
   #14 = Utf8               java/lang/Object
   #15 = Utf8               java/lang/annotation/Annotation

For more examples of order discussions see the recent discussion on 
enhanced-metadata-spec-discuss at openjdk.java.net on annotation ordering in 
reflection and javax.lang.model.

cheers
/Joel