The Android SDK is composed of modular packages that you can download separately using the Android SDK Manager. For example, when the SDK Tools are updated or a new version of the Android platform is released, you can use the SDK Manager to quickly download them to your environment. Simply follow the procedures described in Adding Platforms and Packages.
There are several different packages available for the Android SDK. The table below describes most of the available packages and where they're located once you download them.
Available Packages
| Package | Description | File Location |
|---|---|---|
| SDK Tools | Contains tools for debugging and testing, plus other utilities that are required to develop an app. If you've just installed the SDK starter package, then you already have the latest version of this package. Make sure you keep this up to date. | <sdk>/tools/ |
| SDK Platform-tools | Contains platform-dependent tools for developing and debugging your application. These tools support the latest features of the Android platform and are typically updated only when a new platform becomes available. These tools are always backward compatible with older platforms, but you must be sure that you have the latest version of these tools when you install a new SDK platform. | <sdk>/platform-tools/ |
| Documentation | An offline copy of the latest documentation for the Android platform APIs. | <sdk>/docs/ |
| SDK Platform | There's one SDK Platform available for each version of Android. It includes an android.jar file with a fully compliant Android library. In order to build an Android app, you must specify an SDK platform as your build target. |
<sdk>/platforms/<android-version>/ |
| System Images | Each platform version offers one or more different system images (such as for ARM and x86). The Android emulator requires a system image to operate. You should always test your app on the latest version of Android and using the emulator with the latest system image is a good way to do so. | <sdk>/platforms/<android-version>/ |
| Sources for Android SDK | A copy of the Android platform source code that's useful for stepping through the code while debugging your app. | <sdk>/sources/ |
| Samples for SDK | A collection of sample apps that demonstrate a variety of the platform APIs. These are a great resource to browse Android app code. The API Demos app in particular provides a huge number of small demos you should explore. | <sdk>/platforms/<android-version>/samples/ |
| Google APIs | An SDK add-on that provides both a platform you can use to develop an app using special Google APIs and a system image for the emulator so you can test your app using the Google APIs. | <sdk>/add-ons/ |
| Android Support | A static library you can include in your app sources in order to use powerful APIs that aren't available in the standard platform. For example, the support library contains versions of the Fragment class that's compatible with Android 1.6 and higher (the class was originally introduced in Android 3.0) and the ViewPagerAPIs that allow you to easily build a side-swipeable UI. |
<sdk>/extras/android/support/ |
| Google Play Billing | Provides the static libraries and samples that allow you to integrate billing services in your app with Google Play. | <sdk>/extras/google/ |
| Google Play Licensing | Provides the static libraries and samples that allow you to perform license verification for your app when distributing with Google Play. | <sdk>/extras/google/ |
The above table is not comprehensive and you can add new sites to download additional packages from third-parties.
In some cases, an SDK package may require a specific minimum revision of another package or SDK tool. For example, there may be a dependency between the ADT Plugin for Eclipse and the SDK Tools package. When you install the SDK Tools package, you should also upgrade to the required version of ADT (if you are developing in Eclipse). In this case, the major version number for your ADT plugin should always match the revision number of your SDK Tools (for example, ADT 8.x requires SDK Tools r8).
The development tools will notify you with debug warnings if there is dependency that you need to address. The Android SDK Manager also enforces dependencies by requiring that you download any packages that are needed by those you have selected.
