An Android library project is a development project that holds shared Android source code and resources. Other Android application projects can reference the library project and, at build time, include its compiled sources in their .apk files.
An Android library project is a development project that holds everything needed to build an app, including source code, resource files, and an Android manifest. However, instead of compiling into an APK that runs on a device, an Android library compiles into an Android Archive (AAR) file that can be used as a dependency for an Android app module.
Android Team started revamping the whole design of Android library project since SDK r14 and is going to move from source-based mechanism to compiled-code based library mechanism, in order to support distributing Android library project as a single self-contained jar file. More details in their official blog.
A library module is useful in the following situations:
- When you're building multiple apps that use some of the same components, such as activities, services, or UI layouts.
- When you're building an app that exists in multiple APK variations, such as a free and paid version and you need the same core components in both.
