Number of formal parameters of anonymous class constructor

[konstantin barzilovich]

Hello Alex,

Thank you for quick response.
I agree that JLS 15.9.5.1 does not prohibit the existence of additional 
parameter, but lets consider A ctor with one explicit formal parameter

public A (Integer i) {}

and anonymous class instance creation expression is:

A a = newOuter().newA(5) {};

In this case, following jls-15.9.5.1-100-B.1:

"...The n'th formal parameter e corresponds to the n-1'th actual argument"

we expect anonymous ctor with second parameter of type Integer. But the 
second parameter will be synthetic Outer.
Doesn't it contradict the assertion?
If it is implementation-free, then we don't know what type of second 
parameter should be.

Thanks,
Konstantin.

On 03.08.2015 21:33, Alex Buckley wrote:
> On 8/3/2015 5:47 AM, konstantin barzilovich wrote:
>> In chapter 15.9.5.1 in JLS signature of anonymous constructor is 
>> described.
>> In case S is inner non-static class (see the minimal example)
>>
>> classOuter {
>>      publicOuter() {}
>>      classA  {
>>          publicA() {}
>>      }
>>      public voidfoo(){
>>          A a =newOuter().newA(){};
>>      }
>> }
>>
>> we expect to have one formal parameter of type Outer according to
>> jls-15.9.5.1-100-B and jls-15.9.5.1-100-B.1.
>
> Let's look at what we have. 'S' is the class A, and with i as the 
> newly created instance of the anonymous class:
>
> a) The immediately enclosing instance of i is the instance of Outer on 
> which foo() was called.
> b) The immediately enclosing instance of i-with-respect-to-A is the 
> instance of Outer produced by "new Outer()".
>
> In 15.9.5.1, the JLS prescribes the form of the anonymous class ctor 
> (note the phrase "implicitly declared"). In particular, the JLS 
> prescribes that (b) is encoded as the first formal parameter of the 
> ctor. I guess you could call it the "receiver parameter" but I won't.
>
> You can see the encoding of (b) via reflection. Compile Outer.java 
> with javac -parameters, then reflect over the anonymous class to get 
> its java.lang.reflect.Constructor, then call getParameters(). Element 
> 0 should return true for isImplicit().
>
>> But I try to get parameters of constructor via reflection and it has two
>> parameters both of type Outer.
>> I guess, the second one is a receiver parameter, but it isn't mentioned
>> in jls-15.9.5.1-100-B.1.
>> Could you please clarify this situation?
>
> The JLS does not prescribe the encoding of (a) into the ctor. It is 
> likely that javac is storing (a) as the second parameter, but that's 
> an implementation detail which javac is free to change. I guess you 
> could call it the "environment parameter" but I won't. Point is, JLS 
> 15.9.5.1 does not prohibit the existence of the second parameter.
>
> If you reflect with getParameters(), element 1 should return false for 
> isImplicit() and true for isSynthetic().
>
> Alex