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Building and Running from the Command Line

By default, there are two build types to build your application using the Gradle build settings: one for debugging your application — debug — and one for building your final package for release — release mode. Regardless of which build type your modules use, the app must be signed before it can install on an emulator or device—with a debug key when building in debug mode and with your own private key when building in release mode.

Whether you're building with the debug or release build type, you need to run and build your module. This will create the .apk file that you can install on an emulator or device. When you build using the debug build type, the .apk file is automatically signed by the SDK tools with a debug key based on the debuggable true setting in the module's build.gradle file, so it's instantly ready for installation onto an emulator or attached development device. You cannot distribute an application that is signed with a debug key. When you build using the release build type, the .apk file is unsigned, so you must manually sign it with your own private key, using Keytool and Jarsigner settings in the module's build.gradle file.

It's important that you read and understand Signing Your Applications, particularly once you're ready to release your application and share it with end-users. That document describes the procedure for generating a private key and then using it to sign your APK file. If you're just getting started, however, you can quickly run your applications on an emulator or your own development device by building in debug mode.

If you don't have Gradle, you can obtain it from the Gradle home page. Install it and make sure it is in your executable PATH. Before calling Gradle, you need to declare the JAVA_HOME environment variable to specify the path to where the JDK is installed.

Note: When using ant and installing JDK on Windows, the default is to install in the "Program Files" directory. This location will cause ant to fail, because of the space. To fix the problem, you can specify the JAVA_HOME variable like this:

set JAVA_HOME=c:\Progra~1\Java\<jdkdir>

The easiest solution, however, is to install JDK in a non-space directory, for example:


Building in Debug Mode

For immediate application testing and debugging, you can build your application in debug mode and immediately install it on an emulator. In debug mode, the build tools automatically sign your application with a debug key and optimize the package with zipalign.

To build in debug mode, open a command-line and navigate to the root of your project directory. Use Gradle to build your project in debug mode, invoke the assembleDebug build task using the Gradle wrapper script (gradlew assembleRelease).

This creates your debug .apk file inside the module build/ directory, named <your_module_name>-debug.apk. The file is already signed with the debug key and has been aligned with zipalign.

On Windows platforms, type this command:

> gradlew.bat assembleDebug

On Mac OS and Linux platforms, type these commands:

$ chmod +x gradlew
$ ./gradlew assembleDebug

The first command (chmod) adds the execution permission to the Gradle wrapper script and is only necessary the first time you build this project from the command line.

After you build the project, the output APK for the app module is located in app/build/outputs/apk/, and the output AAR for any lib modules is located in lib/build/outputs/libs/.

To see a list of all available build tasks for your project, type this command:

$ ./gradlew tasks

Each time you change a source file or resource, you must run Gradle again in order to package up the latest version of the application.

To install and run your application on an emulator, see the section about Running on the Emulator.

Building in Release Mode

When you're ready to release and distribute your application to end-users, you must build your application in release mode. Once you have built in release mode, it's a good idea to perform additional testing and debugging with the final .apk.

Before you start building your application in release mode, be aware that you must sign the resulting application package with your private key, and should then align it using the zipalign tool. There are two approaches to building in release mode: build an unsigned package in release mode and then manually sign and align the package, or allow the build script to sign and align the package for you.

Build unsigned

If you build your application unsigned, then you will need to manually sign and align the package.

To build an unsigned .apk in release mode, open a command-line and navigate to the root of your module directory. Invoke the assembleRelease build task.

On Windows platforms, type this command:

> gradlew.bat assembleRelease

On Mac OS and Linux platforms, type this command:

$ ./gradlew assembleRelease

This creates your Android application .apk file inside the project bin/ directory, named <your_module_name>-unsigned.apk.

Note: The .apk file is unsigned at this point and can't be installed until signed with your private key.

Once you have created the unsigned .apk, your next step is to sign the .apk with your private key and then align it with zipalign. To complete this procedure, read Signing Your Applications.

When your .apk has been signed and aligned, it's ready to be distributed to end-users. You should test the final build on different devices or AVDs to ensure that it runs properly on different platforms.

Build signed and aligned

If you would like, you can configure the Android build script to automatically sign and align your application package. To do so, you must provide the path to your keystore and the name of your key alias in your modules's build.gradle file. With this information provided, the build will prompt you for your keystore and alias password when you build using the release build type and produce your final application package, which will be ready for distribution.

To specify your keystore and alias, open the module build.gradle file (found in the root of the module directory) and add entries for storeFile, storePassword, keyAlias and keyPassword. For example:

storeFile file("myreleasekey.keystore")
keyAlias "MyReleaseKey"

Save your changes. Now you can build a signed .apk in release mode:

  1. Open a command-line and navigate to the root of your module directory.
  2. Edit the build.gradle file to build your project in release mode:

    android {
        defaultConfig { ... }
        signingConfigs {
            release {
                storeFile file("myreleasekey.keystore")
                storePassword "password"
                keyAlias "MyReleaseKey"
                keyPassword "password"
        buildTypes {
            release {
                signingConfig signingConfigs.release

  3. When prompted, enter you keystore and alias passwords.

    Caution: As described above, your password will be visible on the screen.

This creates your Android application .apk file inside the module build/ directory, named <your_module_name>-release.apk. This .apk file has been signed with the private key specified in build.gradle file and aligned with zipalign. It's ready for installation and distribution.

Once built and signed in release mode

Once you have signed your application with a private key, you can install and run it on an emulator or device. You can also try installing it onto a device from a web server. Simply upload the signed .apk to a web site, then load the .apk URL in your Android web browser to download the application and begin installation. (On your device, be sure you have enabled Settings > Applications > Unknown sources.)

Running on the Emulator

Before you can run your application on the Android Emulator, you must create an AVD.

To run your application:

  1. Open the AVD Manager and launch a virtual device

    From your SDK's platform-tools/ directory, execute the android tool with the avd options:

    android avd

    In the Virtual Devices view, select an AVD and click Start.

  2. Install your application

    From your SDK's tools/ directory, install the .apk on the emulator:

    adb install <path_to_your_bin>.apk

    Your .apk file (signed with either a release or debug key) is in your module build/ directory after you build your application.

    If there is more than one emulator running, you must specify the emulator upon which to install the application, by its serial number, with the -s option. For example:

    adb -s emulator-5554 install path/to/your/app.apk

    To see a list of available device serial numbers, execute adb devices.

If you don't see your application on the emulator, try closing the emulator and launching the virtual device again from the AVD Manager. Sometimes when you install an application for the first time, it won't show up in the application launcher or be accessible by other applications. This is because the package manager usually examines manifests completely only on emulator startup.

Be certain to create multiple AVDs upon which to test your application. You should have one AVD for each platform and screen type with which your application is compatible. For instance, if your application compiles against the Android 4.0 (API Level 14) platform, you should create an AVD for each platform equal to and greater than 4.0 and an AVD for each screen type you support, then test your application on each one.

Tip: If you have only one emulator running, you can build your application and install it on the emulator in one simple step. Navigate to the root of your project directory and use Ant to compile the project with install mode: ant install. This will build your application, sign it with the debug key, and install it on the currently running emulator.

Running on a Device

Before you can run your application on a device, you must perform some basic setup for your device:

  • Enable USB debugging on your device.
    • On most devices running Android 3.2 or older, you can find the option under Settings > Applications > Development.
    • On Android 4.0 and newer, it's in Settings > Developer options.

      Note: On Android 4.2 and newer, Developer options is hidden by default. To make it available, go to Settings > About phone and tap Build number seven times. Return to the previous screen to find Developer options.

  • Ensure that your development computer can detect your device when connected via USB

Read Setting up a Device for Development for more information.

Once your device is set up and connected via USB, navigate to your SDK's platform-tools/ directory and install the .apk on the device:

adb -d install path/to/your/app.apk

The -d flag specifies that you want to use the attached device (in case you also have an emulator running).

For more information on the tools used above, please see the following documents:

Application Signing

As you begin developing Android applications, understand that all Android applications must be digitally signed before the system will install them on an emulator or device. There are two ways to do this: with a debug key (for immediate testing on an emulator or development device) or with a private key (for application distribution).

The Android build tools help you get started by automatically signing your .apk files with a debug key at build time. This means that you can build your application and install it on the emulator without having to generate your own private key. However, please note that if you intend to publish your application, you must sign the application with your own private key, rather than the debug key generated by the SDK tools.

Please read Signing Your Applications, which provides a thorough guide to application signing on Android and what it means to you as an Android application developer. The document also includes a guide to publishing and signing your application.

Android Plugin for Gradle

The Android build system uses the Android plugin for Gradle to support the Gradle Domain Specific Language (DSL) and declarative language elements. See the Android Plug-in for Gradle section for a description of the plugin and a link to the complete list of the supported Gradle DSL elements.