Towards Understanding Android APIs: Official Lists, Vendor Customizations, and Real-World Usage

TL;DR

This study systematically compares four official Android API lists, analyzing their evolution, inconsistencies, and impact on research, revealing significant discrepancies and vendor API usage in real-world apps.

Contribution

It provides the first comprehensive empirical analysis of official Android API lists, highlighting their instability and influence on research outcomes.

Findings

Official AALs are unstable and inconsistent across Android versions.

Vendor-customized APIs are widely used by apps but often overlooked in research.

Differences among AALs can significantly affect empirical Android studies.

Abstract

Android apps are built on APIs that abstract core Android system functionalities. These APIs are officially documented in multiple files distributed with the Android source code or SDK, which we collectively refer to as Android API Lists (AALs). Prior Android research has relied on specific AALs, often treating them as interchangeable ground truth. However, recent studies suggest that different AALs can lead to substantially different research outcomes, raising concerns about the validity and reproducibility of Android API-based analyses. To address this issue, we present the first in-depth empirical study of four official AALs that are widely used in prior work. We systematically characterize their contents and analyze their evolution across Android releases. We then perform a fine-grained comparison of the APIs recorded in each AAL to uncover their underlying API inclusion policies and inconsistencies. To assess the practical impact of these differences, we further examine API availability on nine Android devices, including both stock Android and vendor-customized systems. Finally, we analyze API usage in 17,759 real-world Android apps (including open-source apps, commercial apps, and malware) to quantify how the choice of AAL affects empirical Android research. Our results reveal that official AALs are neither stable nor mutually consistent, and that discrepancies among them can substantially influence research conclusions. We also observe that vendor-customized APIs are actively used by normal apps, yet remain largely overlooked by existing studies. Based on these findings, we discuss their implications for Android API-based research and provide actionable suggestions to help researchers select and interpret AALs more reliably.