I am trying to better understand the AbstractBackendlessCollection class but I do not see any definition in the Backendless Java SDK : https://github.com/Backendless/Android-SDK
I do see that import com.backendless.commons.AbstractBackendlessCollection in several class files but I cannot find in the GitHub repository.
Some classes of Backendless Android SDK are contained in a dependency com.backendless.commons, which is in the Backendless' repository.
AbstractBackendlessCollection is one of them.
Edit: the repository is actually public, not private, and is located at maven.backendless.com. Still you cannot edit these sources though.