But before you start, there are two fundamental concepts you should understand about Android apps. Apps provide multiple entry points
Android apps are built as a combination of components that can be invoked individually. For example, an activity is a type of app component that provides a user interface.
The "main" activity is what starts when the user taps your app icon, but you can take the user straight into a different activity from other places, such as from a notification or even from a different app.
Other components such as broadcast receivers and services also allow your app to perform background tasks without a user interface. Apps adapt to different devices
Android allows you to provide different resources for different devices. For example, you can create different layouts for different screen sizes. Then the system determines which layout to use based on the current device's screen size.

If any of your app's features need specific hardware, such as a camera, you can query whether the device has that hardware at run time and then disable the corresponding features if not. You can also set some features as required so Google Play won't allow installation on devices without them.
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ANDROID APPLICATION DEVELOPMENT

Solutions and resources for cross platform mobile app developers

Nearly every app you build will use services external to the mobile device. Whether it's from in the cloud or on-premise systems, modern cross platform mobile apps rely on API's, cloud back-ends, and cloud processing. Move code closer to the data. Scale your apps. Optimize code. Deploy whenever and wherever needed. Test, monitor, and update dynamically with ease. As your mobile apps integrate cloud services, you'll also want to bring your mobile skills to the cloud, becoming full-stack developers. Find the resources you need here to rapidly deliver engaging, personalized apps that are valuable to your users and companies.

Build your first app
The following pages teach you how to build a simple Android app. You'll learn how to create a "Hello World" project with Android Studio and run it. Then, you'll create a new interface for the app that takes some user input and opens a second screen in the app.
But before you start, there are two fundamental concepts you should understand about Android apps. Apps provide multiple entry points
Android apps are built as a combination of components that can be invoked individually. For example, an activity is a type of app component that provides a user interface.
The "main" activity is what starts when the user taps your app icon, but you can take the user straight into a different activity from other places, such as from a notification or even from a different app.
Other components such as broadcast receivers and services also allow your app to perform background tasks without a user interface. Apps adapt to different devices
Android allows you to provide different resources for different devices. For example, you can create different layouts for different screen sizes. Then the system determines which layout to use based on the current device's screen size.

If any of your app's features need specific hardware, such as a camera, you can query whether the device has that hardware at run time and then disable the corresponding features if not. You can also set some features as required so Google Play won't allow installation on devices without them.