Can not call a private method, no idea why ?

[forax at univ-mlv.fr]

> De: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
> À: "Anna Kozlova" <anna.kozlova at jetbrains.com>, "Remi Forax" <forax at univ-mlv.fr>
> Cc: "compiler-dev" <compiler-dev at openjdk.java.net>
> Envoyé: Jeudi 21 Janvier 2021 12:20:20
> Objet: Re: Can not call a private method, no idea why ?

> I agree with this analysis. This has nothing to do with default methods, and
> interfaces in general:

> $ cat Test.java
> import java.util.function.Function;

> class Test {
> private void greet() { System.out.println("hello"); }

> void test(Function<? super Object, ? extends Test> f) {
> f.apply(null).greet();
> }
> }

> This still fails. As Anna points out, the function returns `? extends Test`, so
> the compiler cannot assume that what will be returned by the function will be
> "exactly" a Test. If it's a subclass, then the method will be inaccessible,
> even for the VM.
If you have a classical method, like the one below, test can also be a subclass, still you can access to the private method 
void test(Test test) { 
test.greet(); 
} 

Here, because Function is a parametrized type, you need a wildcard to have subtyping, so in both cases you have subtyping, 
but the compiler doesn't behave the same way. 

> Maurizio
Rémi 

> On 21/01/2021 10:53, Anna Kozlova wrote:

>> Hi Remi,

>> type of `map.apply(null)` is capture of `? extends IOBug` and thus it has no
>> access to private methods of IOBug. Do I miss something?

>> Thanks,
>> Anna

>> On Thu, Jan 21, 2021 at 9:34 AM Remi Forax < [ mailto:forax at univ-mlv.fr |
>> forax at univ-mlv.fr ] > wrote:

>>> The following code doesn't compile.
>>> No idea why ?

>>> public interface IOBug {
>>> private IOBug foo() {
>>> return this;
>>> }

>>> default IOBug flatMap(Function<? super Object, ? extends IOBug> map) {
>>> return map.apply(null).foo();
>>> ^------
>>> }
>>> }

>>> It works if foo is declared as a default method instead of a private method.

>>> regards,
>>> Rémi
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