Where can I find Android source code online?

Particularly, where can I browse the source code for any android source application(e.g.the contact application) ? Is the only way to go to download all there is?

Everything is mirrored on omapzoom.org. Some of the code is also mirrored on github.

Contacts is here for example.

Since December 2019, you can use the new official public code search tool for AOSP: cs.android.com. There's also the Android official source browser (based on Gitiles) has a web view of many of the different parts that make up android. Some of the projects (such as Kernel) have been removed and it now only points you to clonable git repositories.

To get all the code locally, you can use the repo helper program, or you can just clone individual repositories.

And others:

• Downloading the Source Tree

2020: The official AOSP code search https://cs.android.com/

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You can view the source code through http://developer.android.com, when you're reading the API there will be a link to the matching source code on GitHub, you just need to add the Android SDK Reference Search Plugin on Chrome.

I blogged about it here:
http://blog.blundellapps.com/add-source-code-links-to-android-apis/

I stumbled across Android XRef the other day and found it useful, especially since it is backed by OpenGrok which offers insanely awesome and blindingly fast search.

I've found a way to get only the Contacts application:

git clone https://android.googlesource.com/platform/packages/apps/Contacts

which is good enough for me for now, but doesn't answer the question of browsing the code on the web.

You can browse Android SDK samples from your smartphone using "Code Search": https://market.android.com/details?id=sqwady.codesearch

This eclipse plugin allows for inline source viewing and even stepping inside the Android source code:

http://code.google.com/p/adt-addons/

(edit: specifically the "Android Sources" plugin: http://adt-addons.googlecode.com/svn/trunk/source/com.android.ide.eclipse.source.update/)

gitweb will allow you to browse through the code (and changes) via a browser.

http://git.or.cz/gitwiki/Gitweb

(Don't know if someone has already setup a public gitweb for Android, but it's probably not too hard.)