Modular Programming in Java 9

Pattern 9 - Design for changes

As with building any API, you have to keep your users in mind when you'll eventually plan to change it. Thus, you'll have to keep possible future changes in mind when you design it! The exported packages in your module are the public API, so your users could be accessing any of them. This means that changing any types in the exported packages of your module will need to be approached with caution, as it could potentially break any consumers of your module.

Of course, this depends on the change itself. If you are adding a new type to an exported package, or are adding new member variables or methods to existing exported types, the changes are still backward compatible. But if you want to remove member variables ...