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page.title=Flexible Framework

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<blockquote>Android's flexible framework means it runs on more devices and reaches more

users</blockquote>

<p>Android powers millions of devices around the world and in a variety of form-factors. The Android

framework is specially built to run apps on more than just one screen size and hardware

configuration. As an app developer, Android's scale and variety offers you the potential to quickly

reach millions of users.</p>

<p>Android apps are flexible and easily adapt to the device on which they are running. Although the

system scales your assets when necessary, you can provide alternative app resources that are

optimized for specific device categories, such as the screen size and density. Android applies the

appropriate resources when running your app, based on the current device’s configuration.</p>

<blockquote>You're in control of which devices can install your app</blockquote>

<p>Some devices provide a different user experience when using apps, but you’re always in control of

how your app behaves on each device. If you publish your app on Google Play, you also have

control over which kinds of devices are allowed to install your app and you can closely control how

your app is distributed.</p>

<p>Every device that includes Google Play has been certified compatible. This means that

the device has passed a rigorous test suite to ensure that the device uses a version of Android that

supports all the platform APIs and will successfully run your app.</p>

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page.title=Open Marketplace

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<p>Android offers an open distribution model, not a walled garden. Once you’ve developed an

app for Android and want to distribute it, you have choice.</p>

<p>Your final application is contained in an APK file that you can make available to users any

way you want. For example, you can upload it to your own web site to allow visitors to

install it onto their devices. More often, you’ll want to use a trusted

marketplace where users can discover and search for your apps.</p>

<p>How you choose to distribute your app affects precisely how many users your app will reach. Which

distribution provider you choose also affects the kinds of services available to you as a publisher,

such as licensing and in-app billing APIs, user bug reports, installation analytics, marketing

services, and more.</p>

<p>Among your choices is Google Play, the premier marketplace for selling and distributing apps

to Android users around the world. When you publish an app on Google Play, you reach hundreds of

millions of customers in over 130 countries.</p>

<h3>Your business, your customers</h3>

<blockquote>Google Play makes your apps available to your customers

immediately</blockquote>

<p>As an open marketplace, Google Play puts you in control of your business and makes it easy for

you to manage how you sell your products. You can publish whenever you want, as often as you want,

and to the exact set of customers you want.</p>

<h3>Visibility for your apps</h3>

<p>Beyond growing your customer base, Google Play helps you build visibility and engagement across

your apps and brand. As your apps rise in popularity, Google Play gives you higher placement in

weekly "top" lists and offers promotional slots in curated collections. You can engage customers

using rich, colorful product pages that feature app screenshots, videos, and user reviews, as well

as cross-marketing links to your other products.</p>

<h3>Flexible monetizing and distribution</h3>

<blockquote class="right">You can distribute

your apps free or priced and you can sell in-app products for additional revenue</blockquote>

<p>Google Play offers a choice of monetizing options to meet your business needs. You control the

pricing of your apps and in-app products—you can set and change prices at any time, even

individually in local currencies around the world. On purchase, Google Play handles transactions in

the buyer’s currency and makes payouts in your own currency.</p>

<p>After publishing, you can manage the distribution of your app. You can distribute broadly to all

markets and devices or focus on specific segments, devices, or ranges of hardware capabilities.

Google Play provides the tools for controlling distribution and ensures that your app is available

only to the users who you are targeting.</p>

page.title=App Framework

@jd:body

<p>Android is a software stack for mobile devices that includes an operating

system, middleware and key applications. The <a

href="http://developer.android.com/sdk/index.html">Android SDK</a>

provides the tools and APIs necessary to begin developing applications on the

Android platform using the Java programming language.</p>

<h2>Features</h2>

<ul>

    <li><strong>Application framework</strong> enabling reuse and replacement

    of components</li>

    <li><strong>Dalvik virtual machine</strong> optimized for mobile

        devices</li>

    <li><strong>Integrated browser</strong> based on the open source <a

    href="http://webkit.org/">WebKit</a> engine </li>

    <li><strong>Optimized graphics</strong> powered by a custom 2D graphics library; 3D

    graphics based on the OpenGL ES 1.0 specification (hardware acceleration

    optional)</li>

    <li><strong>SQLite</strong> for structured data storage</li>

    <li><strong>Media support</strong> for common audio, video, and still

    image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG,

    GIF)</li>

    <li><strong>GSM Telephony</strong> (hardware dependent)</li>

    <li><strong>Bluetooth, EDGE, 3G, and WiFi</strong> (hardware dependent)</li>

    <li><strong>Camera, GPS, compass, and accelerometer</strong> (hardware dependent)</li>

    <li><strong>Rich development environment</strong> including a device

    emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE</li>

</ul>

<a name="os_architecture" id="os_architecture"></a>

<h2>Android Architecture</h2> 

<p>The following diagram shows the major components of the Android operating

system. Each section is described in more detail below.</p>

<p><img src="{@docRoot}images/system-architecture.jpg" alt="Android System Architecture" width="713" height="512"></p>

<a name="applications" id="applications"></a>

<h2>Applications</h2>

<p>Android will ship with a set of core applications including an email

client, SMS program, calendar, maps, browser, contacts, and

others. All applications are written using the Java programming language.</p>

<a name="application_framework" id="application_framework"></a>

<h2>Application Framework</h2>

<p>By providing an open development platform, Android

offers developers the ability to build extremely rich and innovative

applications. Developers are free to take advantage of the

device hardware, access location information, run background services, set alarms,

add notifications to the status bar, and much, much more. </p>

<p>Developers have full access to the same framework APIs used by the core

applications. The application architecture is designed to simplify the reuse

of components; any application can publish its capabilities and any other

application may then make use of those capabilities (subject to security

constraints enforced by the framework). This same mechanism allows components

to be replaced by the user.</p>

<p>Underlying all applications is a set of services and systems, including:

<ul>

    <li>A rich and extensible set of <a

    href="{@docRoot}resources/tutorials/views/index.html">Views</a> that can be used to

    build an application, including lists, grids, text boxes, buttons, and even

    an embeddable web browser</li>

    <li><a href="{@docRoot}guide/topics/providers/content-providers.html">Content

    Providers</a> that enable applications to access data from other

    applications (such as Contacts), or to share their own data</li> <li>A <a

    href="{@docRoot}guide/topics/resources/resources-i18n.html">Resource

    Manager</a>, providing access to non-code resources such as localized

    strings, graphics, and layout files</li>

    <li>A {@link android.app.NotificationManager Notification Manager} that enables

    all applications to display custom alerts in the status bar</li>

    <li>An {@link android.app.Activity Activity Manager} that manages the

    lifecycle of applications and provides a common navigation backstack</li>

</ul>

<p>For more details and a walkthrough of an application, see the <a

href="{@docRoot}training/notepad/index.html">Notepad Tutorial</a>.</p>

<a name="libraries" id="libraries"></a>

<h2>Libraries</h2>

<p>Android includes a set of C/C++ libraries used by various components of the

Android system. These capabilities are exposed to developers through the

Android application framework. Some of the core libraries are listed below:</p>

<ul>

    <li><strong>System C library</strong> - a BSD-derived implementation of

    the standard C system library (libc), tuned for embedded Linux-based

    devices</li>

    <li><strong>Media Libraries</strong> - based on PacketVideo's OpenCORE;

    the libraries support playback and recording of many popular audio and video

    formats, as well as static image files, including MPEG4, H.264, MP3, AAC,

    AMR, JPG, and PNG</li>

    <li><strong>Surface Manager</strong> - manages access to the display

    subsystem and seamlessly composites 2D and 3D graphic layers from multiple

    applications</li>

    <li><strong>LibWebCore</strong> - a modern web browser engine which

    powers both the Android browser and an embeddable web view</li>

    <li><strong>SGL</strong> - the underlying 2D graphics

    engine</li>

    <li><strong>3D libraries</strong> - an implementation based on

    OpenGL ES 1.0 APIs; the libraries use either hardware 3D acceleration

    (where available) or the included, highly optimized 3D software

    rasterizer</li>

    <li><strong>FreeType</strong> - bitmap and vector font rendering</li>

    <li><strong>SQLite</strong> - a powerful and lightweight relational

    database engine available to all applications</li>

</ul>

<a name="runtime" id="runtime"></a>

<h2>Android Runtime</h2>

<p>Android includes a set of core libraries that provides most of

the functionality available in the core libraries of the Java programming

language.</p>

<p>Every Android application runs in its own process, with its own instance of

the Dalvik virtual machine. Dalvik has been written so that a device can run

multiple VMs efficiently. The Dalvik VM executes files in the Dalvik

Executable (.dex) format which is optimized for minimal memory

footprint. The VM is register-based, and runs classes

compiled by a Java language compiler that have been transformed into the .dex

format by the included &quot;dx&quot; tool.</p>

<p>The Dalvik VM relies on the Linux kernel for underlying functionality such

as threading and low-level memory management.</p>

<a name="kernel" id="kernel"></a>

<h2>Linux Kernel</h2>

<p>Android relies on Linux version 2.6 for core system services such as

security, memory management, process management, network stack, and driver

model. The kernel also acts as an abstraction layer between the hardware and

the rest of the software stack.</p>