Android Interview Questions and Answers (Basic)

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 3.0

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 ?

Intent intent = new Intent(Intent.ACTION_VIEW);
Uri u = Uri.parse("http://google.com");
intent.setData(u);
startActivity(intent);

//Function called when return from a sub activity.

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

//How to retrieve the device IMEI Number

TelephonyManager mTelephonyMgr = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
imei = mTelephonyMgr.getDeviceId(); 

How to call a subactivity?

Intent intent = new Intent(this, SubActivity.class);
//to pass data
addintent.putExtra(name, value);
startActivityForResult(intent, int);