Modular Programming in Java 9

Example

Look at the sample code at 09-module-patterns/04-optional-dependencies-with-services.We have two modules, pattern.four and pattern.four.optlib. We want pattern.four to optionally depend on pattern.four.optlib using the services pattern we've seen so far.

The module pattern.four contains a service type LibInterface that it exports. It also declares that it uses provider implementations of LibInterface, which is what essentially makes LibInterface a service type:

    module pattern.four { 
      exports pattern.four.external; 
      uses pattern.four.external.LibInterface; 
    } 

The module pattern.four.optlib provides an implementation of the LibInterface service type. It also depends on pattern.four to access the service type in the first place. This ...