In Jenkins project we have started extending API to support Jenkins Pipeline in some case. We use default implementations in interfaces and abstract classes for it. Recent example: https://github.com/jenkinsci/jenkins/pull/2975/

Problem: Both old AbstractProject/AbstractBuild and new Job/Run methods have default implementations, Java code does not require overrides.

I propose to add a new annotation to https://github.com/kohsuke/access-modifier, which would fail the compilation if the method is not overridden. It would allow us to evolve the API more smoothly.