Projects overview

A project in Android Studio contains everything that defines your workspace for an app, from source code and assets, to test code and build configurations. When you start a new project, Android Studio creates the necessary structure for all your files and makes them visible in the Project window on the left side of the IDE (click View > Tool Windows > Project). This page provides an overview of the key components inside your project.

Modules

A module is a collection of source files and build settings that allow you to divide your project into discrete units of functionality. Your project can have one or many modules and one module may use another module as a dependency. Each module can be independently built, tested, and debugged.

Additional modules are often useful when creating code libraries within your own project or when you want to create different sets of code and resources for different device types, such as phones and wearables, but keep all the files scoped within the same project and share some code.

You can add a new module to your project by clicking File > New > New Module.

Android Studio offers a few distinct types of module:

Android app module
Provides a container for your app's source code, resource files, and app level settings such as the module-level build file and Android Manifest file. When you create a new project, the default module name is "app".

In the Create New Module window, Android Studio offers the following types of app modules:

  • Phone & Tablet Module
  • Wear OS Module
  • Android TV Module
  • Glass Module

They each provide essential files and some code templates that are appropriate for the corresponding app or device type.

For more information on adding a module, read Add a Module for a New Device.

Feature module
Represents a modularized feature of your app that can take advantage of Play Feature Delivery. For example, with feature modules, you can provide your users with certain features of your app on-demand or as instant experiences through Google Play Instant.

To learn more, read Add support for Play Feature Delivery.

Library module
Provides a container for your reusable code, which you can use as a dependency in other app modules or import into other projects. Structurally, a library module is the same as an app module, but when built, it creates a code archive file instead of an APK, so it can't be installed on a device.

In the Create New Module window, Android Studio offers the following library modules:

  • Android Library: This type of library can contain all file types supported in an Android project, including source code, resources, and manifest files. The build result is an Android Archive (AAR) file that you can add as a dependency for your Android app modules.
  • Java Library: This type of library can contain only Java source files. The build result is an Java Archive (JAR) file that you can add as a dependency for your Android app modules or other Java projects.
Google Cloud module
Provides a container for your Google Cloud backend code. This module has the required code and dependencies for a Java App Engine backend that uses simple HTTP, Cloud Endpoints, and Cloud Messaging to connect to your app. You can develop your backend to provide cloud services your app needs.

Using Android Studio to develop your Google Cloud module lets you manage app code and backend code in the same project. You can also run and test your backend code locally, and use Android Studio to deploy your Google Cloud module.

For more information on running and deploying a Google Cloud module, see Running, Testing, and Deploying the Backend.

Some people also refer to modules as sub-projects and that's okay, because Gradle also refers to modules as projects. For example, when you create a library module and want to add it as a dependency to your Android app module, you must declare it as follows:

dependencies {
  compile project(':my-library-module')
}

Project files

By default, Android Studio displays your project files in the Android view. This view does not reflect the actual file hierarchy on disk, but is organized by modules and file types to simplify navigation between key source files of your project, hiding certain files or directories that are not commonly used. Some of the structural changes compared to the structure on disk include the following:

  • Shows all the project's build-related configuration files in a top-level Gradle Script group.
  • Shows all manifest files for each module in a module-level group (when you have different manifest files for different product flavors and build types).
  • Shows all alternative resource files in a single group, instead of in separate folders per resource qualifier. For example, all density versions of your launcher icon are visible side-by-side.

Within each Android app module, files are shown in the following groups:

manifests
Contains the AndroidManifest.xml file.
java
Contains the Java source code files, separated by package names, including JUnit test code.
res
Contains all non-code resources, such as XML layouts, UI strings, and bitmap images, divided into corresponding sub-directories. For more information about all possible resource types, see Providing Resources.

The Android project view

To see the actual file structure of the project including all files hidden from the Android view, select Project from the dropdown at the top of the Project window.

When you select Project view, you can see a lot more files and directories. The most important of which are the following:

module-name/
build/
Contains build outputs.
libs/
Contains private libraries.
src/
Contains all code and resource files for the module in the following subdirectories:
androidTest/
Contains code for instrumentation tests that run on an Android device. For more information, see the Android Test documentation.
main/
Contains the "main" sourceset files: the Android code and resources shared by all build variants (files for other build variants reside in sibling directories, such as src/debug/ for the debug build type).
AndroidManifest.xml
Describes the nature of the application and each of its components. For more information, see the AndroidManifest.xml documentation.
java/
Contains Java code sources.
jni/
Contains native code using the Java Native Interface (JNI). For more information, see the Android NDK documentation.
gen/
Contains the Java files generated by Android Studio, such as your R.java file and interfaces created from AIDL files.
res/
Contains application resources, such as drawable files, layout files, and UI string. See Application Resources for more information.
assets/
Contains file that should be compiled into an .apk file as-is. You can navigate this directory in the same way as a typical file system using URIs and read files as a stream of bytes using the AssetManager . For example, this is a good location for textures and game data.
test/
Contains code for local tests that run on your host JVM.
build.gradle (module)
This defines the module-specific build configurations.
build.gradle (project)
This defines your build configuration that apply to all modules. This file is integral to the project, so you should maintain them in revision control with all other source code.

For information about other build files, see Configure Your Build.

Project structure settings

To change various settings for your Android Studio project, open the Project Structure dialog by clicking File > Project Structure. It contains the following sections:

  • SDK Location: Sets the location of the JDK, Android SDK, and Android NDK that your project uses.
  • Project: Sets the version for Gradle and the Android plugin for Gradle, and the repository location name.
  • Modules: Allows you to edit module-specific build configurations, including the target and minimum SDK, the app signature, and library dependencies. See Modules, below.

Modules

The Modules settings section lets you change configuration options for each of your project's modules. Each module's settings page is divided into the following tabs:

  • Properties: Specifies the versions of the SDK and build tools to use to compile the module.
  • Signing: Specifies the certificate to use to sign your APK.
  • Flavors: Lets you create multiple build flavors, where each flavor specifies a set of configuration settings, such as the module's minimum and target SDK version, and the version code and version name. For example, you might define one flavor that has a minimum SDK of 15 and a target SDK of 21, and another flavor that has a minimum SDK of 19 and a target SDK of 23.
  • Build Types: Lets you create and modify build configurations, as described in Configuring Gradle Builds. By default, every module has debug and release build types, but you can define more as needed.
  • Dependencies: Lists the library, file, and module dependencies for this module. You can add, modify, and delete dependencies from this pane. For more information about module dependencies, see Configuring Gradle Builds.