Generation of synthesized parameters

Peter Jensen peter.jensen at
Wed Jan 30 12:47:55 PST 2013

On 01/29/13 17:14, Alex Buckley wrote:
> I have been looking into the JLS treatment of the constructs mentioned 
> below, with an eye to clarifying matters in JLS8.
> I think a construct emitted by javac should be marked as synthesized 
> if it corresponds to a construct declared implicitly in source code. 
> Constructs declared implicitly in source code are:
> - default constructors (8.8.9)
> - the initial parameters of constructors for non-private inner member 
> classes and anonymous classes (13.1,

Did you mean "non-static" ?

Local classes constructors also gets an initial parameter.

> - the values and valueOf methods of enums (8.9.2)
> - certain public fields of enums (8.9.2)
> - certain public methods of interfaces (9.2)
> So for the purpose of this thread, only the second item need be marked 
> synthesized.
> Alex
> On 1/29/2013 12:14 PM, Joe Darcy wrote:
>> Hello,
>> On 1/29/2013 11:40 AM, Eric McCorkle wrote:
>>> In order to facilitate writing tests for the MethodParameters feature,
>>> I'd like to get a complete list of all the cases when javac can 
>>> generate
>>> synthesized parameters.
>>> Here is a list I've put together from email discussions and comments
>>> in JBS:
>>> 1) outer "this" parameters
>> Arguably, some outer this parameters would be *synthesized* with others
>> would be *synthetic*.
>> Inner classes that are also member classes, (see diagram in "Nested,
>> Inner, Member, and Top-Level Classes,"
>>, are
>> potentially callable from outside of the enclosing class and are
>> required to have an outer this parameter as the first parameter so that
>> code from different compilers can call each other.  The other this
>> parameter in this case is *synthesized* as it is mandated or implied by
>> the JLS.
>> On the other hand, named inner classes defined inside a method or
>> constructor as well as anonymous classes only need to obey a
>> compiler-internal contract and any extra parameters in this case are
>> *synthetic*.  (Not all anonymous classes have an outer; an anonymous
>> class created inside a static initializer block does not.)
>>> 2) extra values passed to constructor for enum values
>> Such parameters are *synthetic*, they are a javac implementation
>> artifact not mandated or implied by the JLS.
>>> 3) hidden values passed to constructors of inner classes for final
>>> variables
>> You'll can check the JLS regarding whether these are synthesized or
>> synthetic, but I would assume they are synthetic.
>>> 4) JLS mandated public no-arg constructors added by the compiler to
>>> classes with no declared constructor: synthesized
>> This is not a parameter, but another language structure.
>> HTH,
>> -Joe
>>> 5) The two parameters pre-ended to enum constructors by javac
>>> Does this capture everything, or does it miss something?
>>> Ideally, I would like to put together a complete list of all cases that
>>> should generate synthesized parameters.  (If one already exists, then
>>> that's great).
>>> Thanks,
>>> Eric

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