3_software/3_6_api-namespaces.md

## 3.6\. API Namespaces

Android follows the package and class namespace conventions defined by the Java
programming language.  To ensure compatibility with third-party applications,
device implementers MUST NOT make any prohibited modifications (see below) to
these package namespaces:

*   `java.*`
*   `javax.*`
*   `sun.*`
*   `android.*`
*   `androidx.*`
*   `com.android.*`

That is, they:

*    [C-0-1] MUST NOT modify the publicly exposed APIs on the Android platform
     by changing any method or class signatures, or by removing classes or class
     fields.
*    [C-0-2] MUST NOT add any publicly exposed elements (such as classes or
     interfaces, or fields or methods to existing classes or interfaces) or Test
     or System APIs to the APIs in the above namespaces. A “publicly exposed
     element” is any construct that is not decorated with the “@hide” marker as
     used in the upstream Android source code.

Device implementers MAY modify the underlying implementation of the APIs, but
such modifications:

*    [C-0-3] MUST NOT impact the stated behavior and Java-language signature of
     any publicly exposed APIs.
*    [C-0-4] MUST NOT be advertised or otherwise exposed to developers.

However, device implementers MAY add custom APIs outside the standard Android
namespace, but the custom APIs:

*    [C-0-5] MUST NOT be in a namespace owned by or referring to another
     organization. For instance, device implementers MUST NOT add APIs to the
     `com.google.*` or similar namespace: only Google may do so. Similarly,
     Google MUST NOT add APIs to other companies' namespaces.
*    [C-0-6] MUST be packaged in an Android shared library so that only apps
     that explicitly use them (via the <uses-library> mechanism) are
     affected by the increased memory usage of such APIs.

If a device implementer proposes to improve one of the package namespaces above
(such as by adding useful new functionality to an existing API, or adding a new
API), the implementer SHOULD visit [source.android.com](
http://source.android.com/) and begin the process for contributing changes and
code, according to the information on that site.

Note that the restrictions above correspond to standard conventions for naming
APIs in the Java programming language; this section simply aims to reinforce
those conventions and make them binding through inclusion in this Compatibility
Definition.