ClientAPI

From APIDesign

There is a difference between ClientAPI and ProviderAPI evolution rules. As soon as you publish an API targeted for others to call, you, as publisher of your library, want to have the freedom to satisfy additional requirements of users of your library. What additional requirements can you expect? In case the only use of your API is that it can be called, then the common requirement is going to be a request to expose more methods and to allow the users to call more functionality.

What is the most suitable coding construct in Java to support backward compatible additions of new methods? The most safe one is a final class. As such it is suggested to expose only final classes to users of ClientAPI. If you publish non-final class, or even interface, you'll face evolution problems as described at ExtendingInterfaces.