Lesson 4 - How is the Android Software Developed

How is the Android software developed?
Each platform version of Android (such as 1.5, 1.6, and so

on) has a corresponding branch in the open-source tree. At
any given moment, the most recent such branch will be
considered the "current stable" branch version. This
current stable branch is the one that manufacturers port to
their devices. This branch is kept suitable for release at all
times.
Simultaneously,there is also a "current experimental"
branch, which is where speculative contributions, such as
large next-generationfeatures, are developed. Bug fixes
and other contributions can be included in the current
stable branch from the experimental branch as
appropriate.
Finally, Google works on the next version of the Android
platform in tandem with developing a flagship device. This
branch pulls in changes from the experimental and stable
branches as appropriate.
You can find more information on this topic at our
Branches and Releases.
Why are parts of Android developed in private?
It typically takes over a year to bring a device to market,
but of course device manufacturers want to ship the latest
software they can. Developers, meanwhile, don't want to
have to constantly track new versions of the platform when
writing apps. Both groups experience a tension between
shipping products, and not wanting to fall behind.
To address this, some parts of the next version of Android
including the core platform APIs are developed in a private
branch. These APIs constitute the next version of Android.
Our aim is to focus attention on the current stable version
of the Android source code, while we create the next
version of the platform as driven by flagship Android
devices. This allows developers and OEMs to focus on a
single version without having to track unfinished future
work just to keep up. Other parts of the Android system
that aren't related to application compatibility are
developed in the open, however. It's our intention to move
more of these parts to open development over time.
When are source code releases made?
When they are ready. Some parts of Android are developed
in the open, so that source code is always available.
Other
parts are developed first in a private tree, and that source
code is released when the next platform version is ready.
In some releases, core platform APIs will be ready far
enough in advance that we can push the source code out
for an early look in advance of the device's release;
however in others, this isn't possible. In all cases, we
release the platform source when we feel the version has
stabilized enough, and when the development process
permits. Releasing the source code is a fairly complex
process.