About Question enthuware.ocpjp.ii.v11.2.3444 :

[teodorj]

For example,
if an abc.print module implements an org.printing.Print service interface defined in PrintServiceAPI module using com.abc.PrintImpl class,
then this is how its module-info should look:

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module abc.print{
	requires PrintServiceAPI; //required because this module defines the service interface org.printing.Print
	provides org.printing.Print with com.abc.PrintImpl;
}

I notice that

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requires PrintServiceAPI;

does not use module name same with package name (org.printing.PrintServiceApi).

Module name with same name as package is optional and best practice right?

[admin]

Yes, it is a best practice but not a requirement. In this case, the problem statement says that the module is PrintServiceAPI, so that is why the module abc.Print's module-info has "requires PrintServiceAPI;" clause.

[pavvel]

In Explanation we have a next example:

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module abc.print{
    requires PrintServiceAPI; //required    
    //because this module defines the service interface org.printing.Print
    provides org.printing.Print with com.abc.PrintImpl; 
}

Is this correct that, nobody can uses com.abc.PrintImpl, due to lack of the exports word?

[admin]

Nobody refers to PrintImpl class directly. Other modules who want to use the Print service use the Print interface only (which is in PrintServiceAPI module). So exporting the package containing PrintImpl from abc.print module is not required. In fact, it is not even recommended to export com.abc.PrintImpl from ab.print module because you don't want anyone to accidently start using PrintImpl directly.

[dameest]

Hello, the response in this question assumes that the service is defined in another module, which is not stated in the question. Isn't it possible for a module implementing a service to also contains the interface?

[admin]

It is indeed possible for a module that defines the service to also provide an implementation and vice-versa. But that is not a requirement. The problem statement specifically say "implements a service", it does not say "defines the service interface" so it is best not to assume that. This is especially true about modules because the general practice is to keep the service definition and service implementation separate.