Generated parameter names for -parameters (JEP118)

Jesper Steen Møller jesper at
Wed May 29 15:09:01 PDT 2013

Jonathan Gibbons wrote:
> I think you should be more explicit in what you think is wrong,
>instead of just posting a javap dump and expecting others to
>read through it.

I'm sorry -- you are quite right. I should have explained the problem properly.

The problem is with the MethodParameters attribute for the anonymous inner class' constructor.

> With respect to your question,
>Why do you think an entry is missing from the table?

The constructor code has three arguments: The this reference itself, the enclosing class' this reference, and the value of the captured final variable of the enclosing scope.
The descriptor shows the two "non-this" arguments: (LParameterNames;Ljava/lang/String;)V

As I understand, the MethodParameters attribute should describe the latter two parameters here, matching the method descriptor, but it doesn't quite:
The hex dump of the MethodParameters table is this:
MethodParameters: length = 0x5
02 00 0A 80 10
Length byte

From what I've read in '4.7.22 The MethodParameters Attribute', the length should be 9, since there's one byte for the length, and four bytes for each parameter.

u1 parameters_count = 0x02
parameters [2] = {
parameter {
  u2 name_index == 0x000A //  'this$0' in the constant pool
  u2 access_flags == 0x8010 // meaning MANDATED+FINAL
parameter {
    // MISSING!

Also, I'm also suspecting that the entry is in error since javap didn't properly decode it and show the actual parameter names, as it can for other classes. 

>What entry do you think is missing from the table?

The second one, containing the name of the captured local variable from the enclosing context. I'm sure this doesn't really have a name, since no code ac
I'm expecting it to be synthetic and final 0x1010, but I could be mistaken.

FWIW, this is from build 1.8.0-ea-b90.

TIA, Jesper

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