In Android documentation there is an article about "Performance Tips" that recommends avoiding theuse of internal getters/setters. A recent publication in the MOBILESoft 2016 conference agrees with this recommendation.
However, according to the lint documentation:
As of Android 2.3 (Gingerbread), this optimization is performed automatically by Dalvik, so there is no need to change your code; this is only relevant if you are targeting older versions of Android.
Is there any official and updated information regarding this?