What is the importance of module descriptors in modules in Java 9?

A module is organized in the form of package and static resources (such as property files or others) A collection of classes. It provides the external environment with all the information needed to use the module. The module descriptor is the key source of the module system, it is the compiled version of the module declaration, located in the root directory of the module directory hierarchy named "module-info.java" in the file.

A module describes itself through the following module declaration

<strong>module com.myproject.module1 {
   requires com.myproject.module2;
   exports com.myproject.project1;
   exports com.myproject.project2;
}</strong>

The following are descriptions of some module descriptors:

• module module. name: Declare a module named module.name.
• requires module. name: Specifies that our module depends on module.name, allowing the module to access public types exported in the target module.
• requires a transitive module. name: Any module that depends on this module will automatically depend on module.name.
• exports pkg.name: It means that our module exports the public members in the package pkg.name for every module that requires this module.
• exports pkg.name to module.name: Same as above, but restricts the modules that can use public members in package pkg.name.
• uses class. name: It makes the current module a consumer of service class.name.
• provides class.name with class.name.impl: It registers a class.name.impl class that implements the class.name service as a service.
• opens pkg.name: It allows other modules to use reflection to access private members in package pkg.name.
• opens pkg.name to module.name: It is the same as above, but restricts which modules can use reflection to access private members in pkg.name.

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