Basic Android Interview question & answer

What is Android ?
Android is a software stack for mobile devices that includes an operating system, middleware and key applications.

Explain the Architecture of android ?
Top -> Applications (Contacts, Browser, Phone, etc)

Below Applications -> Application Framework(Activity Manager, Window Manager, Content Providers, View System, Package manager,
Telephony manager, Resource, Notification, Location managers)

Below Application Framework -> System Libraries(Like Sqlite, webkit, SSL, OpenGL, Media Framework etc) & Android Runtime( Core Libraries and DVM)

Atlast Last -> Linux Kernel (which composed of drivers like display, camera etc.)

Describe the APK format.
The APK file is compressed the AndroidManifest.xml file, application code (.dex files), resource files, and other files.
A project is compiled into a single .apk file.

What is an action ?
A description of something that an Intent sender desires.

What is an activity ?
A single screen in an application, with supporting Java code.
An activity presents a visual user interface for one focused endeavor the user can undertake.
For example, an activity might present a list of menu items users can choose from or it might display photographs along with their captions.
Each one is implemented as a subclass of the Activity base class.

What is a service ?
A service doesn’t have a visual user interface, but rather runs in the background for an indefinite period of time.
For example, a service might play background music as the user attends to other matters, or it might fetch data over the network or calculate
something and provide the result to activities that need it.
Each service extends the Service base class.

What is a Broadcast receivers ?
A broadcast receiver is a component that does nothing but receive and react to broadcast announcements.
For example, announcements that the timezone has changed, that the battery is low or that the user changed a language preference.
All receivers extend the BroadcastReceiver base class.
Broadcast receivers do not display a user interface. However, they may start an activity in response to the information they receive,
or they may use the NotificationManager to alert the user like(flashing the backlight, vibrating the device, playing a sound)

What is a content provider ?
A content provider makes a specific set of the application’s data available to other applications.The content provider extends the ContentProvider
base class to implement a standard set of methods that enable other applications to retrieve and store data of the type it controls.
However, applications do not call these methods directly. Rather they use a ContentResolver object and call its methods instead.

What is intent ?
A class (Intent) describes what a caller desires to do. The caller sends this intent to Android’s intent resolver, which finds the most suitable activity for the intent.

How is nine-patch image different from a regular bitmap ?
It is a resizable bitmap resource that can be used for backgrounds or other images on the device. The NinePatch class permits drawing a bitmap in nine sections. The four corners are unscaled; the four edges are scaled in one axis, and the middle is scaled in both axes.

What languages does Android support for application development ?
Android applications are written using the Java programming language.

What is a resource ?
A user-supplied XML, bitmap, or other file, injected into the application build process, which can later be loaded from code.

What Virtual Machine Android runs on ?
Dalvik virtual machine

Android Latest Version ?
Android 4.4 KitKat 

 What do containers hold ?
 Containers hold objects and widgets in a specified arrangement.
 They can also hold labels, fields, buttons, or child containers. .

What are the key components of Android Architecture ?
Android Architecture consists of 4 key components:
Linux Kernel
Libraries
Android Framework
Android Applications

What are the advantages of having an emulator within the Android environment?
The emulator allows the developers to work around an interface which acts as if it were an actual mobile device.
They can write, test and debug the code.
They are safe for testing the code in early design phase

Tell us something about activityCreator ?
An activityCreator is the initial step for creation of a new Android project.
It consists of a shell script that is used to create new file system structure required for writing codes in Android IDE.

What do intent filters do ?
There can be more than one intents, depending on the services and activities that are going to use them.
Each component needs to tell which intents they want to respond to.
Intent filters filter out the intents that these components are willing to respond to.

Where are layout details placed? Why ?
Layout details are placed in XML files
XML-based layouts provide a consistent and standard means of setting GUI definition format.

What is Orientation ?
Orientation decides if the LinearLayout should be presented in row wise or column wise fashion.
The values are set using setOrientation()
The values can be HORIZONTAL or VERTICAL

What is it important to set permissions in app development ?
Certain restrictions to protect data and code can be set using permissions.
In absence of these permissions, codes could get compromised causing defects in functionality.

What is AIDL ?
AIDL is the abbreviation for Android Interface Definition Language.
It handles the interface requirements between a client and a service to communicate at the same level through interprocess communication.
The process involves breaking down objects into primitives that are Android understandable.

What data types are supported by AIDL ?
AIDL supports following data types:
-String
-List
-Map
-charSequence and all native Java data types like int,long, char and Boolean

Which dialog boxes are supported by android ?
Android supports 4 dialog boxes:

a.) AlertDialog: Alert dialog box supports 0 to 3 buttons and a list of selectable elements which includes check boxes and radio buttons.

b.) ProgressDialog: This dialog box is an extension of AlertDialog and supports adding buttons. It displays a progress wheel or bar.

c.) DatePickerDialog: The user can select the date using this dialog box.

d.) TimePickerDialog: The user can select the time using this dialog box.

How do you define the user interface ?
XML Format is the best.

Code Snippets:
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How to start a browser instance with some url ?

1	Intent intent = new Intent(Intent.ACTION_VIEW);

2	Uri u = Uri.parse("http://google.com");

3	intent.setData(u);

4	startActivity(intent);

//Function called when return from a sub activity.

1	protected void onActivityResult(int requestCode, int resultCode, String data, Bundle extras) {

2

}

//How to retrieve the device IMEI Number

1	TelephonyManager mTelephonyMgr = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);

2	imei = mTelephonyMgr.getDeviceId();

How to call a subactivity ?

1	Intent intent = new Intent(this, SubActivity.class);

2	//to pass data

3	addintent.putExtra(name, value);

4	startActivityForResult(intent, int);