"Provides" and "with" type relationships

[Alex Buckley]

Yes. 'uses' and 'provides' are nothing more than static declarations 
that configure java.util.ServiceLoader, so all questions can be resolved 
by looking at the ServiceLoader spec: 
http://download.java.net/java/jigsaw/docs/api/java/util/ServiceLoader.html

Alex

On 3/16/2016 10:24 AM, Konstantin Barzilovich wrote:
> 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
>>>
>>>
>
>