Introduction and architecture

Question 1

What is Android?

Answer 1

Googles open and free software stack that includes:
- OS Kernel
- System Libraries
- Application Framework
- Key applications for use on Android mobile devices

Question 2

What is the Android SDK?

Answer 2

Android Software Development Kit contains the tools and packaged for creating android applications.

Question 3

From innermost to outermost, what are the 5 layers of the Android platform architecture?

Answer 3

Linux Kernel
HAL
C/C++ Libraries and Android Runtime Environment
Java API Framework
System Applications

Question 4

What is the role of the Linux Kernel in Android?

Answer 4

Security; process and low level memory management; File and network IO; Hardware drivers; Power Management.

Question 5

What is the role of the Hardware Abstraction layer (HAL) in Android?

Answer 5

Interfaces the hardware components to the Java API Framework. Each hardware component has 1 interface, and each interface is implemented by one or more libraries. Thus, enabling developers to interact with the hardware. For example, Audio, Camera, Sensors etc.

Question 6

What type of processes are native C libraries used for? What are some of the responsibilities that Android Runtime takes care of?

Answer 6

Used for intensive, computationally heavy processes. Native C libraries include Webkit, OpenGL, SQLite.
Android Runtime is the android runtime environment that includes classes, app lifecycle, unit testing etc.

Question 7

What is the role of the Java API Framework layer in Android?

Answer 7

Promotes and enables the reuse of system components and services.

Question 8

What is the role of the System Applications layer in Android?

Answer 8

Any of the core applications that android provides. For example, calendar, email, browser, camera etc.

Question 9

How does Android Runtime work?

Answer 9

1. Program is written in Java
2. Java code is converted to Bytecode
3. Bytecode is converted to DEX Bytecode files
4. DEX Bytecode files are input into the Android Runtime Environment
5. ART outputs the executable files, which are specifically optimised for devices with constraints on memory and speed.

Question 10

Where are the application resources kept within the project strcture?

Answer 10

In the res folder

Question 11

What is the R class? What is it an ancestor to?

Answer 11

Exists solely to link resources to the Java code.
It is an ancestor of all files in the res folder.

Question 12

How does accessing valued of the R class differ between the doing so in Java code and doing so through XML?

Answer 12

R.string.hello -> Java code
@string/hello -> XML

Question 13

What are the 4 application components?

Answer 13

Activity, Service, Broadcast Receiver, Content Provider.

Question 14

Define the Activity component…What must be done before they can be used?

Answer 14

Provides points of interaction for the user.
Each activity is a subclass of Activity.
GUI widgets are implemented within Activities.
They must be registered with the Applications manifest before they are used.

Question 15

Define the Services component…

Answer 15

• Consists of long running processes that take place in the background.
  For example, playing music or the reminders app.
• Services usually run on their hosting processes thread.

Question 16

Define the Broadcast Receivers component…

Answer 16

• A dormant component that listens to system wide broadcast events and intents. System wide meaning across all applications on the device.
• Each broadcast receiver must register with a broadcast event. Thus, the receiver is notified when that broadcast occurs.
• System broadcasts include low battery, power connected etc.
• Custom broadcasts are used to notify other apps

Question 17

Define the Content Provider…

Answer 17

• Component that enables and facilitates secure interaction with the applications central repository of data.
• Provides a client object that external or internal components can interact with. This objet the carries out transactions onto the central data repository based on requests.
• For example, a Task App would use a Content Provider to add and remove tasks from the application.
• Provide an abstraction layer that other applications or inter-application components have to interact in order to access the data.

Question 18

Give an advantage of Android using a Linux Kernel?

Answer 18

Linux is widely used, thus it’s easy for manufacturers to develop for.

Question 19

Explain the role of the Hardware Abstraction Layer…

Answer 19

Provides interfaces that expose hardware components to the Java API Framework. The HAL contains library modules, each of which implements one of the interfaces of a hardware component.

Question 20

When a call to a hardware component is made, which library module is called?

Answer 20

The library model that implements the HAL interface for that hardware component.

Question 21

What change was made in Android 5 regarding the Android Runtime Environment when an application is run?

Answer 21

Each Application was given its own instance of the Android Runtime Environment.

Question 22

What is the purpose of native C/C++ libraries in the platform architecture?

Answer 22

Many core components of the Android System are built in C and C++. For example, Android Runtime Environment and the Hardware Abstraction Layer are build in C based languages.

The Java API Framework exposes the functionality of these native libraries.

Question 23

What is the Manifest file?

Answer 23

A document at the root of the project structure. The Manifest contains vital application information such as components used, permissions, hardware and software requirements.

The Manifest acts as the system-wide face of your application. The Android System uses the manifest to locate your app, search your app and communicate with your app.