Android Question how to create service by JAVA and be used in B4A?

I want to learn to create service in Java and build to lib,and be used in B4A.
Till now ,i know how to create project in Eclipse,and build by SLC.
I appreciate if there is service source code by JAVA i could learn about,maybe parts of them.
like this:
https://www.b4x.com/android/forum/t...er-library-notificationlistenerservice.35630/
https://www.b4x.com/android/forum/t...ervice-and-has-abstract-public-methods.31546/