Google android white paper

1. INTRODUCTION
Android as a system is a java based operating system that runs on the Linux 2.6 kernel,
based on Apache Harmony (http://harmony.apache.org) and a custom virtual machine
called as Dalvik .
In terms of software terminology, Android is a software stack for mobile devices that
includes an operating system, middleware and key applications. The Android SDK
provides the tools and APIs necessary to begin developing applications on the Android
platform using the Java programming language.
2. Why Android?
There has been big barrier of broad scope of embedded devices software especially if we talk
about the operating systems of embedded devices. Still abundantly used embedded device like
mobile phones are still living on proprietary operating systems, to work on those systems
developers have to pay heavy price to purchase development environment and build-linker-
debugging tools. This leads to slow development in overall mobile development field, since lots
of homebrew developers unable to put their research and development knowledge.
This barrier to application development began to crumble in November of 2007 when
Google, under the Open Handset Alliance, released Android. The Open Handset Alliance
is a group of hardware and software developers, including Google, NTT DoCoMo,
Sprint Nextel, and HTC, whose goal is to create a more open cell phone environment.
The first product to be released under the alliance is the mobile device operating
system, Android. (For more information about the Open Handset Alliance, see
www.openhandsetalliance.com.)
With the release of Android, Google made available a host of development tools
and tutorials to aid would-be developers onto the new system. Help files, the platform
software development kit (SDK), and even a developers’ community can be found at
Google’s Android website, http://code.google.com/android. This site should be your
starting point and I highly encourage you to visit the site.

3. Android System Architecture
Figure 1. Android System Architecture
3.1 Applications: Basic applications include an email client, SMS program, calendar, maps,
browser, contacts, and others. All applications are written in Java programming language.
3.2 Application Framework: The developers have full access to the same framework APIs
used by applications base. The architecture is designed to simplify the reuse of components, any
application can publish its capabilities and any other application can then make use of those
capabilities (subject to safety rules framework). This same mechanism allows components to be
replaced by the user.
3.3 Libraries: Android includes a set of libraries C / C + + used by various components of the
Android system. These features are exposed to developers through the Android application
framework, some of them: System C library (C standard library implementation), media libraries,
graphics libraries, 3d, SQLite, and others.
3.4 Runtime Android: Android includes a set of base libraries that provide most of the features
available in the libraries of the Java language base. Every Android application runs 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. Dalvik executes files in the Dalvik Executable (. Dex),
which is optimized for minimum memory. The virtual machine is based on records, and runs
classes compiled by the Java compiler that have been transformed by the tool to formato.dex
included “dx”.
3.5 Kernel – Linux: Android depends on Linux version 2.6 for basic services such as security
system, memory management, process management, network stack and driver model. The kernel
also acts as an abstraction layer between hardware and the rest of the software stack.
4. What Androids Are Made Of
When you write a desktop application, you are “master of your own domain.” You launch your
main window and any child windows—like dialog boxes—that are needed. From your
standpoint, you are your own world, leveraging features supported by the operating system, but
largely ignorant of any other program that may be running on the computer at the same time.
If you do interact with other programs, it is typically through an API, such as using JDBC (or
frameworks atop it) to communicate with MySQL or another database.
Android has similar concepts, but packaged differently, and structured to make phones more
crash-resistant.
4.1 Activities
The building block of the user interface is the activity. You can think of an activity as being the
Android analogue for the window or dialog in a desktop application.
While it is possible for activities to not have a user interface, most likely your “headless” code
will be packaged in the form of content providers or services, like the following described.
4.2 Content Providers
Content providers provide a level of abstraction for any data stored on the device that is
accessible by multiple applications. The Android development model encourages you to make
your own data available to other applications, as well as your own—building a content provider
lets you do that, while maintaining complete control over how your data gets accessed.
4.3 Intents
Intents are system messages, running around the inside of the device, notifying applications of
various events, from hardware state changes (e.g., an SD card was inserted), to incoming data
(e.g., an SMS message arrived), to application events (e.g., your activity was launched from the
device’s main menu). Not only can you respond to intents, but you can create your own, to launch
other activities, or to let you know when specific situations arise (e.g., raise such-andso intent
when the user gets within 100 meters of this-and-such location).

4.4 Services
Activities, content providers, and intent receivers are all short-lived and can be shut down at any
time. Services, on the other hand, are designed to keep running, if needed, independent of any
activity. You might use a service for checking for updates to an RSS feed, or to play back music
even if the controlling activity is no longer operating.
An Android application, along with a file called AndroidManifest.xml, is deployed to a device.
AndroidManifest.xml contains the necessary configuration information to properly install it to the
device. It includes the required class names and types of events the application is able to process,
and the required permissions the application needs to run. For example, if an application requires
access to the network — to download a file, for example — this permission must be explicitly
stated in the manifest file. Many applications may have this specific permission enabled. Such
declarative security helps reduce the likelihood that a rogue application can cause damage on
your device.
5. Other Android features
Android comes with a number of features to help you develop applications.
5.1 Storage
You can package data files with your application, for things that do not change, such as icons or
help files. You also can carve out a small bit of space on the device itself, for databases or files
containing user-entered or retrieved data needed by your application. If the user supplies bulk
storage, like an SD card, you can read and write files on there as needed.
5.2 Network
Android devices will generally be Internet-ready, through one communications medium or
another. You can take advantage of the Internet access at any level you wish, from raw Java
sockets all the way up to a built-in WebKit-based Web browser widget you can embed in your
application.
5.3 Multimedia
Android devices have the ability to play back and record audio and video. While the specifics
may vary from device to device, you can query the device to learn its capabilities and then take
advantage of the multimedia capabilities as you see fit, whether that is to play back music, take
pictures with the camera, or use the microphone for audio note-taking.
6. Android Basics
To start doing development in Android developer should aware about core Java, if developer is
from C++ background, then working on Java code is not that difficult, because OOPS concept are
near about same in C++ or in any other oops language and Java. However the applications are

written in Java but compiled and executed in the Dalvik VM(a non Java virtual machine).
Android development can take place on Microsoft Windows, Mac OS or on Linux.
The simplest way of starting development in Android, starts with downloading latest the latest
Android SDK, the Eclipse IDE and Android plugins for Eclipse. Eclipse is the recommended IDE
for Android development. Using Eclipse for doing coding in Java provide lots of facilities like
context sensitive help and code suggestion hints.
6.1 Android SDK
Android SDK consist documentation for current Android version, Skins for the various supported
hardware, and other Android tools.
6. 2 Configuring Eclipse for Android Plugins
In Eclipse go to Help->Software Updates then “Available softwares” the press “Add Site”. Here
Android plugin can be downloaded by giving http link (https://dl-ssl.google.com/android/eclipse/)
or through locally stored ADT.zip

Figure 1. ADT plugin
Add Android SDK path in Window->Preferences

6.3 Creating New Android Project

Select New->Android Project or New->Other->Android Project. This will start New Project
wizard, where we can create new Android Project and its Test application.
In new project wizard, give a name to Project, application, package and activity. In Android
activity is same as the first screen or Form which is started as default. The name of that entry
goes in AndroidManifest.xml which is generated by this wizard.

Once finish, new Android get created and added to workspace as-

Android project consists of Src folder which keeps the packages and source files correspond to
the individual packages information. Gen folder has R. Java which is generated after compilation
of project. R.java has the java code for resources which are there in res folder. Res folder keeps
the resources as drawable, it has image files, layout it has screen or activity layout xml files and
values, it has strings.xml to store strings used in project. AndroidManifest.xml has project
configuration like activities in the project, default activity, user permission etc.
6.4 Adding “Hello World” code
By default HelloWorld.java created an Activity without UI. For adding UI on this activity,
TextView can be used, TextView is one of the UI element in Android. SetText() function of
TextView set the text”Hello World” on TextView.
package com.android.helloworld;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class HelloWorld extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("Hello, World");
setContentView(tv);
}
}
6.5 Running first Android program

Android SDK is provided with the android platform emulator, which can be customized
according the hardware type by changing the skins of emulator. To start new emulator, we have
to create a android virtual device(avd) which is needed to load new emulator. AVD files has the
emulator virtual hardware configurations. Avd is create by passing command on command line:
android create avd --target 2 --name helloworld_avd
[*Make sure that android SDK and Android SDK tools path are set in environment variables]
AVD is also created by Eclipse by pressing “Device Manager icon on tool bar.
New project, is automatically build, because “Build automatically” is checked on Project menu,
user can uncheck to get the control of building the project.
After creating new avd and build successful, emulator can pressing green play button near device
manager icon on tool bar.
First time when emulator started it will take sometime, and it also depends upon the machine.
Higher the machine RAM, faster the emulator gets up. Once the emulator get started, it will not
required to close the emulator for any change to get affected, because when next time we made
any change the application and tries run, it actually uploaded on existing running emulator, then it
get installed, then its default activity started, which means it get actually running on the emulator.

7. Android Source code:
Android source code is available free or open source till its latest version 2.0 (with is also known
as with code name “Éclair”). Under apache license Android source code for telephony and
network is available on 2.0 and its lower version. In Oct 2009, Google has release Android
2.0(with code name “Éclair”). Android previous versions 1.5(“CupCake”) and 1.6 (“Donut”) are
also available to download and use freely. After 1.6 Google has launched 2.0 since it has said that
2.0 has major updates, hence the number is far beyond 1.6.
Google provide open doors to use Android source code for contributing in further Android
development or using it under Apache license for non Google enterprises.
How to download source and how to build SDK out of it all documentation is available on.
(http://source.android.com/).
7.1 Android source tree:
 Operating System (Linux Kernel version 2.6)
 Middleware in form of libraries for graphics, SQLite, Media and others handheld
hardwares libraries.
 Framework:
• Activity Manager
• Content Providers
• Package manager
• Telephony Manager
• Resource Manager
• Location Manager
• Notification Manager
• View System
• Window Manager
 Key Mobile Applications
• Home (Analogically same as Desktop or Stand by in mobile phones)
• Contacts
• Phone
• Browser

As source code level android is available as several projects already in progress. These projects
can be divided into three categories:
• Core projects: These projects make up the foundation of the Android
platform.
• External projects: The Android Open Source Project makes use of many
other open source projects.
• Packages: These projects are standard Android applications and
services.
7.2 How to take source code and use it?
(Refer http://source.android.com for details)
To work with Android source, we need Git and Repo tools.
Git is a open source version controlling larger project which are distributed on multiple
repositories. In Android, we use Git for local operations such as local branching, commits, diffs,
and edits.
Repo is the tool whch is wrapper of Git which helps in managing different Git repositaries. Repo
is made to work easily with Git. The repo command is the python script which use to do git
manipulation from anywhere on terminals.
7.2.1 Setting up Linux machine
Android source build are tested and working well on Ubuntu(6.06 and later versions).
Ubuntu Linux (32-bit x86)
To set up your Linux development environment, make sure you have the following:
• Required Packages:
o Git 1.5.4 or newer and the GNU Privacy Guard.
o JDK 5.0, update 12 or higher. Java 6 is not supported, because of
incompatibilities with @Override.
o flex, bison, gperf, libsdl-dev, libesd0-dev, libwxgtk2.6-dev (optional), build-
essential, zip, curl.
$ sudo apt-get install git-core gnupg sun-java5-jdk flex bison gperf libsdl-dev libesd0-dev
libwxgtk2.6-dev build-essential zip curl libncurses5-dev zlib1g-dev
• You might also want Valgrind, a tool that will help you find memory leaks, stack
corruption, array bounds overflows, etc.
$ sudo apt-get install valgrind

• Intrepid (8.10) users may need a newer version of libreadline:
$ sudo apt-get install lib32readline5-dev
7.2.2 Installing Repo
Repo is a tool that makes it easier to work with Git in the context of Android. For more information about
Repo, see Using Repo and Git.
To install, initialize, and configure Repo, follow these steps:
1. Make sure you have a ~/bin directory in your home directory, and check to be sure that
this bin directory is in your path:
$ cd ~
$ mkdir bin
$ echo $PATH
2. Download the repo script and make sure it is executable:
$ curl http://android.git.kernel.org/repo >~/bin/repo
$ chmod a+x ~/bin/repo
7.2.3 Initializing a Repo client
1. Create an empty directory to hold your working files:
$ mkdir mydroid
$ cd mydroid
2. Run repo init to bring down the latest version of Repo with all its most recent bug fixes.
You must specify a URL for the manifest:
$ repo init -u git://android.git.kernel.org/platform/manifest.git
o If you would like to check out a branch other than "master", specify it with -b,
like:
$ repo init -u git://android.git.kernel.org/platform/manifest.git -b eclair
3. When prompted, configure Repo with your real name and email address. If you plan to
submit code, use an email address that is associated with a Google account.
A successful initialization will end with a message such as
repo initialized in /mydroid
Your client directory should now contain a .repo directory where files such as the manifest will
be kept.
7.2.4 Getting the files
To pull down files to your working directory from the repositories as specified in the default
manifest, run
$ repo sync

7.2.5 Verifying Git Tags
Load the following public key into your GnuPG key database. The key is used to sign annotated
tags that represent releases.
$ gpg --import
then paste the key(s) below, and press Control-D to end the input and process the keys. After
importing the keys, you can verify any tag with
$ git tag -v tagname
key 9AB10E78: "The Android Open Source Project <initial-contribution@android.com>"
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.4.2.2 (GNU/Linux)
mQGiBEnnWD4RBACt9/h4v9xnnGDou13y3dvOx6/t43LPPIxeJ8eX9WB+8LLuROSV
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-----END PGP PUBLIC KEY BLOCK-----
7.2.6 Building the code
To build the files, run make from within your working directory:
$ cd ~/mydroid
$ make
If your build fails, complaining about a missing "run-java-tool", try setting the ANDROID_JAVA_HOME
env var to $JAVA_HOME before making. E.g.,

$ export ANDROID_JAVA_HOME=$JAVA_HOME
7.2.7 Using an IDE
• Using Eclipse for Android platform development
7.3 Getting Android X86 code
Google has made available Android for x86 platforms like Eee PC(Asus). The Android code for
X86 is available from: http://code.google.com/p/android-x86/wiki/GetSourceCode

References
1. Using Repo and Git -> http://source.android.com/download/using-repo
2. Hello World Tutorial-> http://developer.android.com/guide/tutorials/hello-world.html
3. Download the Android SDK.
4. Get the latest Eclipse IDE.
5. ADT plugin
6. Android source-> http://source.android.com/
7. Beginning Android: Mark L. Murphy
8. Android Programmer’s Guide: Jerome (J. F.) DiMarzio
9. Android developers site (http://developer.android.com/index.html ). It has all the latest of
what’s going on Android.
10. Android FAQs and common tasks -
http://developer.android.com/guide/appendix/faq/commontasks.html

Google android white paper

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