Linux kernel
At the bottom of the
layers is Linux - Linux 3.6 with approximately 115 patches. This provides a
level of abstraction between the device hardware and it contains all the
essential hardware drivers like camera, keypad, display etc. Also, the kernel
handles all the things that Linux is really good at such as networking and a
vast array of device drivers, which take the pain out of interfacing to
peripheral hardware.
Libraries
On top of Linux
kernel there is a set of libraries including open-source Web browser engine
WebKit, well known library libc, SQLite database which is a useful repository
for storage and sharing of application data, libraries to play and record audio
and video, SSL libraries responsible for Internet security etc.
Android Libraries
This category
encompasses those Java-based libraries that are specific to Android
development. Examples of libraries in this category include the application
framework libraries in addition to those that facilitate user interface
building, graphics drawing and database access. A summary of some key core
Android libraries available to the Android developer is as follows −
·
android.app − Provides access to the
application model and is the cornerstone of all Android applications.
·
android.content − Facilitates content access,
publishing and messaging between applications and application components.
·
android.database − Used to access data published
by content providers and includes SQLite database management classes.
·
android.opengl − A Java interface to the OpenGL
ES 3D graphics rendering API.
·
android.os − Provides applications with
access to standard operating system services including messages, system
services and inter-process communication.
·
android.text − Used to render and manipulate
text on a device display.
·
android.view − The fundamental building blocks
of application user interfaces.
·
android.widget − A rich collection of pre-built
user interface components such as buttons, labels, list views, layout managers,
radio buttons etc.
·
android.webkit − A set of classes intended to
allow web-browsing capabilities to be built into applications.
Having covered the
Java-based core libraries in the Android runtime, it is now time to turn our
attention to the C/C++ based libraries contained in this layer of the Android
software stack.
Android Runtime
This is the third section
of the architecture and available on the second layer from the bottom. This
section provides a key component calledDalvik Virtual Machine which
is a kind of Java Virtual Machine specially designed and optimized for Android.
The Dalvik VM makes use of
Linux core features like memory management and multi-threading, which is
intrinsic in the Java language. The Dalvik VM enables every Android application
to run in its own process, with its own instance of the Dalvik virtual machine.
The Android runtime also
provides a set of core libraries which enable Android application developers to
write Android applications using standard Java programming language.
Application Framework
The Application Framework
layer provides many higher-level services to applications in the form of Java
classes. Application developers are allowed to make use of these services in
their applications.
The Android framework
includes the following key services −
·
Activity Manager − Controls all aspects of the application lifecycle and
activity stack.
·
Content Providers − Allows applications to publish and share data with other
applications.
·
Resource Manager − Provides access to non-code embedded resources such as
strings, color settings and user interface layouts.
·
Notifications Manager − Allows applications to display alerts and notifications to
the user.
·
View System − An extensible set of views used to create application user
interfaces.
Applications
You will find all the
Android application at the top layer. You will write your application to be
installed on this layer only. Examples of such applications are Contacts Books,
Browser, Games etc.
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