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Android Introduction
Platform Overview
@2011 Mihail L. Sichitiu
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What is Android?

Android is a software
stack for mobile devices
that includes an
operating system,
middleware and key
applications.
@2011 Mihail L. Sichitiu
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OHA (Open Handset Alliance)
A
business alliance consisting of 47
companies to develop open standards
for mobile devices
@2011 Mihail L. Sichitiu
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Market Share (2014 Q2)
@2011 Mihail L. Sichitiu
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Architecture
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Android S/W Stack - Application
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Android provides a set of core applications:
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Email Client
SMS Program
Calendar
Maps
Browser
Contacts
Etc
All applications are written using the Java language.
@2011 Mihail L. Sichitiu
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Android S/W Stack –
App Framework
 Enabling
and simplifying the reuse of
components
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Developers have full access to the same
framework APIs used by the core applications.
Users are allowed to replace components.
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Android S/W Stack –
App Framework (Cont)
 Features
Feature
Role
View
System
Used to build an application, including lists, grids, text
boxes, buttons, and embedded web browser
Content
Provider
Enabling applications to access data from other
applications or to share their own data
Resource
Manager
Providing access to non-code resources (localized strings,
graphics, and layout files)
Notification
Manager
Enabling all applications to display customer alerts in the
status bar
Activity
Manager
Managing the lifecycle of applications and providing
a common navigation backstack
Window
Manager
Manages the windows comprising an App.
@2011 Mihail L. Sichitiu
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Android S/W Stack - Libraries
 Including
a set of C/C++ libraries used by
components of the Android system
 Exposed to developers through the
Android application framework
@2011 Mihail L. Sichitiu
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Android S/W Stack - Runtime
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Core Libraries
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Providing most of the functionality available in
the core libraries of the Java language
APIs
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Data Structures
Utilities
File Access
Network Access
Graphics
Etc
@2011 Mihail L. Sichitiu
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Android S/W Stack – Runtime
(Cont)
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Dalvik Virtual Machine
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Providing environment on which every Android
application runs
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Each Android application runs in its own process, with
its own instance of the Dalvik VM.
Dalvik has been written such that a device can run
multiple VMs efficiently.
Unlike java VM, Dalvik is designed for resourceconstrained environments
@2011 Mihail L. Sichitiu
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Android S/W Stack – Runtime
(Cont)
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Dalvik Virtual Machine (Cont)
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Executing the Dalvik Executable (.dex) format
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.dex format is optimized for minimal memory
footprint.
Compilation
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Android S/W Stack – Runtime
(Cont)
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Android Runtime (ART)
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ART is a new Android runtime being introduced
experimentally in the 4.4 release.
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Ahead-of-time (AOT) compilation
Improved garbage collection
Development and debugging improvements
@2011 Mihail L. Sichitiu
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Android S/W Stack – Linux Kernel
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Providing an abstraction layer between the H/W and the rest
of the S/W stack
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Relying on Linux Kernel 2.6-3.4 for core system services
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Memory and Process Management and Threading
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Network Stack
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File & Network IO
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Driver Model
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Security
@2011 Mihail L. Sichitiu
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Android S/W Stack – Linux Kernel
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Linux Kernel – Android Specific Components
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Power Management
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Android Shared Memory
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Low Memory Killer
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Interprocess Communication
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Application Fundamentals
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Applications
Written in Java (it’s possible to write
native code – will not cover that here)
 Good separation (and corresponding
security) from other applications:
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Each application runs in its own process
Each process has its own separate VM
Each application is assigned a unique Linux
user ID – by default files of that application are
only visible to that application (can be
explicitly exported)
@2011 Mihail L. Sichitiu
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Application Components
Activities – visual user interface focused
on a single thing a user can do
 Services – no visual interface – they run in
the background
 Broadcast Receivers – receive and react to
broadcast announcements
 Content Providers – allow data exchange
between applications
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Activities
Basic component of most applications
 Most applications have several activities
that start each other as needed
 Each is implemented as a subclass of the
base Activity class
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Activity Lifecycle
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Services
Does not have a visual interface
 Runs in the background indefinitely
 Examples
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Network Downloads
Playing Music
TCP/UDP Server
You can bind to a an existing service and
control its operation
@2011 Mihail L. Sichitiu
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Broadcast Receivers
Receive and react to broadcast
announcements
 Extend the class BroadcastReceiver
 Examples of broadcasts:
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Low battery, power connected, shutdown,
timezone changed, etc.
Other applications can initiate broadcasts
@2011 Mihail L. Sichitiu
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Content Providers
Makes some of the application data
available to other applications
 It’s the only way to transfer data between
applications in Android (no shared files,
shared memory, pipes, etc.)
 Extends the class ContentProvider;
 Other applications use a ContentResolver
object to access the data provided via a
ContentProvider
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Android Manifest

Its main purpose in life is to declare the components to the
system:
<?xml version="1.0" encoding="utf-8"?>
<manifest . . . >
<application . . . >
<activity
android:name="com.example.project.FreneticActivity"
android:icon="@drawable/small_pic.png"
android:label="@string/freneticLabel"
... >
</activity>
...
</application>
</manifest>
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Android ADT – Eclipse IDE
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Android Studio - IntelliJ IDE
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