"Provides" and "with" type relationships

[Konstantin Barzilovich]

Sorry, if this question was asked before.
Does service implementation need to inherit service interface?

Thanks,
Konstantin.

> // Ignore last mail (mail client did a surprising thing)
>
> A 'provides' clause specifies two things: a service interface and a  
> service implementation. Using those terms helps to avoid confusion.
>
> A service interface does not have to be an interface; it can be an  
> abstract class or even (not recommended) a concrete class.
>
> A service implementation must not be an interface, or an abstract class;  
> it must be a concrete class.
>
> Therefore, it's legal (but not recommended) for a concrete class to be  
> specified as both service interface and service implementation. It's  
> illegal for an interface (or abstract class) to be specified as both  
> service interface and service implementation. JCK will be writing tests  
> for edge cases like this.
>
> Alex
>
> On 3/15/2016 12:39 PM, Paul Benedict wrote:
>> Thanks for your response Alex. If I am understanding you correctly,
>> "provides" is "not constrained to be an interface" because it can be "a
>> single interface or abstract class". So shouldn't my concrete class for
>> "provides" be rejected by the compiler? And is it okay that both types
>> were identical?
>>
>> Cheers,
>> Paul
>>
>> On Tue, Mar 15, 2016 at 2:26 PM, Alex Buckley <alex.buckley at oracle.com
>> <mailto:alex.buckley at oracle.com>> wrote:
>>
>>     The first operand to 'provides' (the "service interface") is not
>>     constrained to be an interface by "Modules in the Java Language and
>>     JVM". This is because the spec of j.u.ServiceLoader ("a service is
>>     represented by a single type, that is, a single interface or
>>     abstract class").
>>
>>     The second operand to 'provides' (the "service implementation") is
>>     constrained not to be an interface or an abstract class by "Modules
>>     in the Java Language and JVM". This is also because of the spec of
>>     j.u.ServiceLoader ("provider classes must have a zero-argument
>>     constructor so that they can be instantiated during loading").
>>
>>     Bear in mind that the JCK team can easily set up abstract test cases
>>     like this. What they can't do is check whether YOUR application runs
>>     on JDK-9-with-Jigsaw, or whether arbitrary JARs on YOUR classpath
>>     work as automatic modules.
>>
>>     Alex
>>
>>
>>     On 3/15/2016 12:07 PM, Paul Benedict wrote:
>>
>>         module z {
>>               exports z;
>>               provides z.Main with z.Main;
>>         }
>>
>>         The SOTM says "Service-provider declarations can be further
>>         interpreted to
>>         ensure that providers (e.g., com.mysql.jdbc.Driver) actually do
>>         implement
>>         their declared service interfaces" (section 4, para. 8).
>>
>>         I see javac checking that they are related types, but javac is
>>         not checking
>>         that "provides" is an interface type. That is what I was
>>         expecting based on
>>         the reading material.
>>
>>         The other unexpected outcome was that provides/with allows the
>>         identical
>>         type. I don't know if that's intended, but please advise.
>>
>>         PS: I did go through the open tickets this time (thanks Alan)
>>         and do not
>>         see any similar reports. If I missed it, I apologize; just
>>         trying not to
>>         waste your time by reporting a duplicate.
>>
>>         Cheers,
>>         Paul
>>
>>


-- 
Thanks,
Konstantin.