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 not OK if the same type is
specified as both service interface and service implementation, and JCK
will be writing tests for that, I promise.
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.buck...@oracle.com
<mailto:alex.buck...@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