Bottom-up migration

Now that Java 9 is out of the door, the much-awaited modularity feature is now available to be adopted by developers. At some point or another, you will be involved in migrating your application to Java 9 and, hence, trying to modularize it. A change of such magnitude, which involves third-party libraries and rethinking the code structure, would require proper planning and implementation. The Java team has suggested two migration approaches:

• Bottom-up migration 
• Top-down migration

Before going into learning about bottom-up migration, it's important to understand what an unnamed module and an automatic module are. Suppose you are accessing a type that's not available in any of the modules; in such a case, the module system will search for the type on the classpath, and if found, the type becomes part of an unnamed module. This is similar to the classes we write that do not belong to any package, but Java adds them to an unnamed package so as to simplify the creation of new...