Working with Android code requires using Git (an open-source version-control system) and Repo (a Google-built repository-management tool that runs on top of Git). See Source Control Workflow for a summary of regular actions, such as uploading changes for review.
Git
Git is designed to handle large projects that are distributed over multiple repositories. Android uses Git for local operations such as local branching, commits, diffs, and edits. One of the challenges in setting up the Android project was figuring out how to best support the outside community—from the hobbyist community to large OEMs building mass-market consumer devices. We wanted components to be replaceable, and we wanted interesting components to have a life of their own outside of Android. We first chose a distributed revision control system, then narrowed it down to Git.
For more details on Git, refer to Git Documentation.
Repo
Repo unifies Git repositories when necessary, performs
uploads to the Gerrit revision control system, and automates parts of
the Android development workflow. Repo comes in two parts: The Repo
Launcher that you download from git-repo-downloads is the
first part. It's a Python script that knows how to initialize a checkout and
can download the second part, the full Repo tool. The full
Repo tool is by default in $SRCDIR/.repo/repo/... and receives
forwarded commands from the downloaded Repo Launcher.
Repo isn't meant to replace Git, only to make it easier to work with Git in
the context of Android. It uses
manifest files to aggregate Git projects into the Android
superproject. The repo command is an executable Python script
that you can put anywhere in your path. In working with the Android source
files, you use Repo for across-network operations, for example, with a single
Repo working directory.
In most situations, you can use Git instead of Repo, or mix Repo and Git commands to form complex commands. However, using Repo for basic across-network operations makes your work much simpler. For more details on Repo, see the Repo Command Reference, Repo README, and the Preupload Hooks (tests) that can be enabled in Repo.
Other tools
Gerrit is a web-based code review system for projects that use Git. Gerrit encourages a more centralized use of Git by allowing all authorized users to submit changes, which are automatically merged if they pass code review. In addition, Gerrit makes reviewing easy, displaying changes side by side in the browser and enabling inline comments.
Android Code Search allows you to search AOSP without downloading anything. You can use Code Search to view the AOSP source code, switch between open source branches, and navigate cross-references. For more information, see the Google Developers site for the Code Search documentation.
Android Studio is the official integrated development environment (IDE) for Android app development.