Java annotationprocessing - generating files at each round vs at last round

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Java

Android

annotation

I was playing around with annotation processing and was unable to use generated files directly via an import in my code. Instead I had to prepend the generated classes with its complete package. I (accidentally) figured out the reason for this, turned out to be pretty simple, the error was because I was generating the files at last round of AbstractProcessor. What I had to do was generate files at each round.

So my questions are:

• Are there more differences in generating files at last round vs generating files before the last round?
  
• Is there a specific reason (Java-related or otherwise) for this behavior?
  

I know from the warning that new rounds will not run even if the annotation is present in the new generated files, however I still don't understand how generating files at only the last round changes the way I access classes.

In case it is relevant, I'm working on an Android Project in Android Studio and using JavaPoet to write classes.

What I have tried:

I posted two SO questions:
First
error: package generated.schema does not exist.
But then I figured out the answer on my own and then I posted a follow up question
AnnotationProcessing - Generating Files at Each Round vs at Last Round

I've also gone through a few tutorials on Annotation Processing but I haven't been able to find anything either explaining or hinting at this behavior.