Android Interview questons and Answers

Q: Why to use Android?

A: Android is useful because:

* It is simple and powerful SDK.

* Licensing, Distribution or Development fee is not required.

* Easy to Import third party Java library.

* Supporting platforms are Linux, Mac Os, Windows.

Q: What are the advantages of Android?

A: The following are the advantages of Android:

* The customer will be benefited from wide range of mobile applications to choose, since the monopoly of wireless carriers like AT&T and Orange will be broken by Google's Android.

* Features like weather details, live RSS feeds, icon on the opening screen can be customized

* Innovative products like the location-aware services, location of a nearby convenience store etc., are some of the additive facilities in Android.

* Customer can use most of the google services via Android supported devices.

Q: What is Android?

A: Android is a stack of software for mobile devices which has Operating System, middleware and some key applications. The application executes within its own process and its own instance of Dalvik Virtual Machine. Many Virtual Machines run efficiently by a DVM device. DVM executes Java language's byte code which later transforms into .dex format files.

Q: What are the features of Android?

A: Following are few of the features:

* Components can be reused and replaced by the application framework.

* Optimized DVM for mobile devices

* SQLite enables to store the data in a structured manner.

* Supports GSM telephone and Bluetooth, WiFi, 3G and EDGE technologies

* The development is a combination of a device emulator, debugging tools, memory profiling and plug-in for Eclipse IDE.

Q: Describe Android Application Architecture?

A: Android Application Architecture has the following components:

* Services like Network Operation

* Intent - To perform inter-communication between activities or services

* Resource Externalization - such as strings and graphics

* Notification signaling users - light, sound, icon, notification, dialog etc.

* Content Providers - They share data between applications

Q: Describe the APK format.
A: It is a file which is used to install an Android application. It is a collection of AndroidManifest.xml file, application code (.dex files), resource files, and other files needed for the application/game in a compressed form. It is the final output file after compilation of the source code and resources.

Q: How to Translate in android

A: The Google translator translates the data of one language into another language by using XMPP to transmit data. You can type the message in English and select the language which is understood by the citizens of the country in order to reach the message to the citizens.

Q: What is an action?

A: Description of something that an Intent sender desires.

Q: What is activity?

A: Single screen in an application, with supporting Java code.

Q: What is intent?

A: 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. E.g. opening a PDF file is an intent, and the Adobe Reader is the suitable activity for this intent.

Three of the four component types, activities, services, and broadcast receivers are activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another.

Q: How is nine-patch image different from a regular bitmap?

A: 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.

Q: What languages does Android support for application development?

A: Android applications are written using the Java programming language. You can use C/C++ and even Javascript for web apps.

Q: What is a resource?

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

Q: What's the difference between file, class and activity in android? 

A: File - It is a block of arbitrary information, or resource for storing information. It can be of any type.

Class - Its a compiled form of .Java file . Android finally used this .class files to produce an executable apk

Activity - An activity is the equivalent of a Frame/Window in GUI toolkits. It is not a file or a file type it is just a class that can be extended in Android for loading UI elements on view.

Q: What is a Sticky Intent?

A: sendStickyBroadcast() performs a sendBroadcast (Intent) that is "sticky," i.e. the Intent you are sending stays around after the broadcast is complete, so that others can quickly retrieve that data through the return value of registerReceiver (BroadcastReceiver, IntentFilter). In all other ways, this behaves the same as sendBroadcast(Intent).

One example of a sticky broadcast sent via the operating system is ACTION_BATTERY_CHANGED. When you call registerReceiver() for that action -- even with a null BroadcastReceiver -- you get the Intent that was last broadcast for that action. Hence, you can use this to find the state of the battery without necessarily registering for all future state changes in the battery.

Example for sticky broadcast 

When you call registerReceiver() for that action -- even with a null BroadcastReceiver -- you get the Intent that was last broadcast for that action. Hence, you can use this to find the state of the battery without necessarily registering for all future state changes in the battery.

Q: What is the TTL (Time to Live)? Why is it required?

A: TTL is a value in data packet of Internet Protocol. It communicates to the network router whether or not the packet should be in the network for too long or discarded. Usually, data packets might not be transmitted to their intended destination within a stipulated period of time. The TTL value is set by a system default value which is an 8-bit binary digit field in the header of the packet. The purpose of TTL is, it would specify certain time limit in seconds, for transmitting the packet header. When the time is exhausted, the packet would be discarded. Each router receives the subtracts count, when the packet is discarded, and when it becomes zero, the router detects the discarded packets and sends a message, Internet Control Message Protocol message back to the originating host.

Q: Explain IP datagram, Fragmentation and MTU ?

A: IP datagram can be used to describe a portion of IP data. Each IP datagram has set of fields arranged in an order. The order is specific which helps to decode and read the stream easily. IP datagram has fields like Version, header length, Type of service, Total length, checksum, flag, protocol, Time to live, Identification, source and destination ip address, padding, options and payload.

MTU:- Maximum Transmission Unit is the size of the largest packet that a communication protocol can pass. The size can be fixed by some standard or decided at the time of connection

Fragmentation is a process of breaking the IP packets into smaller pieces. Fragmentation is needed when the datagram is larger than the MTU. Each fragment becomes a datagram in itself and transmitted independently from source. When received by destination they are reassembled.

Q: Explain about the exceptions of Android?

A: The following are the exceptions that are supported by Android

* InflateException : When an error conditions are occurred, this exception is thrown

* Surface.OutOfResourceException: When a surface is not created or resized, this exception is thrown

* SurfaceHolder.BadSurfaceTypeException: This exception is thrown from the lockCanvas() method, when invoked on a Surface whose is SURFACE_TYPE_PUSH_BUFFERS

* WindowManager.BadTokenException: This exception is thrown at the time of trying to add view an invalid WindowManager.LayoutParamstoken.

Q: What are the differences between a domain and a workgroup?

A: In a domain, one or more computer can be a server to manage the network. On the other hand in a workgroup all computers are peers having no control on each other. In a domain, user doesn't need an account to logon on a specific computer if an account is available on the domain. In a work group user needs to have an account for every computer. In a domain, computers can be on different local networks. In a work group all computers needs to be a part of the same local network.

Q: What are the dialog boxes that are supported in android? Explain.

A: Android supports 4 dialog boxes:

AlertDialog: An alert dialog box supports 0 to 3 buttons and a list of selectable elements, including check boxes and radio buttons. Among the other dialog boxes, the most suggested dialog box is the alert dialog box.

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

DatePickerDialog: This dialog box is used for selecting a date by the user.

TimePickerDialog: This dialog box is used for selecting time by the user.

Q: What are the problems publishing to the market?

A: The fragmentation of Android in multiple OS versions. There are various devices in market with different versions of Android OS. Where as new OS are not 100% backward compatible because of various (H/W) reasons. Apart from this, each and every OEM/device manufacturer (like Samsung, Dell, HTC, Motorola, LG etc) customize the UI of the OS on their devices according to their will which fragments the OS with in the same OEM. But from OS version 3.0 or 3.1 it is promised to be taken care. So, lets hope new future devices will be comparatively less fragmented.

Q: How will you record a phone call in Android? How to get a handle on Audio Stream for a call in Android?
A: Permissions.PROCESS_OUTGOING_CALLS: Allows an application to monitor, modify, or abort outgoing calls.

Q: What's the difference between file, class and activity in android?
A: File - It is a block of arbitrary information, or resource for storing information. It can be of any type.
Class - Its a compiled form of .Java file . Android finally used this .class files to produce an executable apk
Activity - An activity is the equivalent of a Frame/Window in GUI toolkits. It is not a file or a file type it is just a class that can be extended in Android for loading UI elements on view.

Q: What is a Sticky Intent?
A: sendStickyBroadcast() performs a sendBroadcast (Intent) that is "sticky," i.e. the Intent you are sending stays around after the broadcast is complete, so that others can quickly retrieve that data through the return value of registerReceiver (BroadcastReceiver, IntentFilter). In all other ways, this behaves the same as sendBroadcast(Intent).

One example of a sticky broadcast sent via the operating system is ACTION_BATTERY_CHANGED. When you call registerReceiver() for that action -- even with a null BroadcastReceiver -- you get the Intent that was last broadcast for that action. Hence, you can use this to find the state of the battery without necessarily registering for all future state changes in the battery.

Android Glossary

.apk extension

The extension for an Android package file, which typically contains all of the files related to a single Android application. The file itself is a compressed collection of an AndroidManifest.xml file, application code (.dex files), resource files, and other files. A project is compiled into a single .apk file.

.dex extension

Android programs are compiled into .dex (Dalvik Executable) files, which are in turn zipped into a single .apk file on the device. .dex files can be created by automatically translating compiled applications written in the Java programming language.

Action

A description of something that an Intent sender wants done. An action is a string value assigned to an Intent. Action strings can be defined by Android or by a third-party developer. For example, android.intent.action.VIEW for a Web URL, or com.example.rumbler.SHAKE_PHONE for a custom application to vibrate the phone.

Activity

A single screen in an application, with supporting Java code, derived from the Activity class.

adb

Android Debug Bridge, a command-line debugging application shipped with the SDK. It provides tools to browse the device, copy tools on the device, and forward ports for debugging. See Using adb for more information.

Application

A collection of one or more activities, services, listeners, and intent receivers. An application has a single manifest, and is compiled into a single .apk file on the device.

Content Provider

A class built on ContentProvider that handles content query strings of a specific format to return data in a specific format. See Reading and writing data to a content provider for information on using content providers.

Content URI

A type of URI. See the URI entry.

Dalvik

The name of Android’s virtual machine. The Dalvik VM is an interpreter-only virtual machine that executes files in the Dalvik Executable (.dex) format, a format that is optimized for efficient storage and memory-mappable execution. The virtual machine is register-based, and it can run classes compiled by a Java language compiler that have been transformed into its native format using the included “dx” tool. The VM runs on top of Posix-compliant operating systems, which it relies on for underlying functionality (such as threading and low level memory management). The Dalvik core class library is intended to provide a familiar development base for those used to programming with Java Standard Edition, but it is geared specifically to the needs of a small mobile device.

DDMS

Dalvik Debug Monitor Service, a GUI debugging application shipped with the SDK. It provides screen capture, log dump, and process examination capabilities. See Using the Dalvik Debug Monitor Server to learn more about this program.

Drawable

A compiled visual resource that can be used as a background, title, or other part of the screen. It is compiled into an android.graphics.drawable subclass.

Intent

A class (Intent) that contains several fields describing what a caller would like to do. The caller sends this intent to Android’s intent resolver, which looks through the intent filters of all applications to find the activity most suited to handle this intent. Intent fields include the desired action, a category, a data string, the MIME type of the data, a handling class, and other restrictions.

Intent Filter

Activities and intent receivers include one or more filters in their manifest to describe what kinds of intents or messages they can handle or want to receive. An intent filter lists a set of requirements, such as data type, action requested, and URI format, that the Intent or message must fulfill. For Activities, Android searches for the Activity with the most closely matching valid match between the Intent and the activity filter. For messages, Android will forward a message to all receivers with matching intent filters.

Intent Receiver

An application class that listens for messages broadcast by calling Context.broadcastIntent(). For example code, see Listening for and broadcasting global messages.

Layout resource

An XML file that describes the layout of an Activity screen.

Manifest

An XML file associated with each Application that describes the various activies, intent filters, services, and other items that it exposes. See AndroidManifest.xml File Details.

Nine-patch / 9-patch / Ninepatch image

A resizeable bitmap resource that can be used for backgrounds or other images on the device. See Nine-Patch Stretchable Image for more information.

Query String

A type of URI. See the URI entry.

Resource

A user-supplied XML, bitmap, or other file, entered into an application build process, which can later be loaded from code. Android can accept resources of many types; see Resources for a full description. Application-defined resources should be stored in the res/ subfolders.

Service

A class that runs in the background to perform various persistent actions, such as playing music or monitoring network activity.

Theme

A set of properties (text size, background color, and so on) bundled together to define various default display settings. Android provides a few standard themes, listed in R.style (starting with “Theme_”).

URIs

Android uses URI strings both for requesting data (e.g., a list of contacts) and for requesting actions (e.g., opening a Web page in a browser). Both are valid URI strings, but have different values. All requests for data must start with the string “content://”. Action strings are valid URIs that can be handled appropriately by applications on the device; for example, a URI starting with “http://” will be handled by the browser

Q: Can I write code for Android using C/C++?
A: 
Android applications are written using the Java programming language.
Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.
Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included “dx” tool.
Android only supports applications written using the Java programming language at this time.

Q: Creating an Android Application using the Eclipse Plugin

A: Using the Android Eclipse plugin is the fastest and easiest way to start creating a new Android application. The plugin automatically generates the correct project structure for your application, and keeps the resources compiled for you automatically.
It is still a good idea to know what is going on though. Take a look at Overview of an Android Application to understand the basics of how an Android application works.
It is also recommended that you take a look at the ApiDemos application and the other sample applications in the samples/ folder in the SDK.
Finally, a great way to started with Android development in Eclipse is to follow both the Hello Android and Notepad code tutorials. In particular, the start of the Hello Android tutorial is an excellent introduction to creating a new Android application in Eclipse.

What is Android Runtime?

Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.
Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included “dx” tool.

Features of Android

• Application framework enabling reuse and replacement of components
• Dalvik virtual machine optimized for mobile devices
• Integrated browser based on the open source WebKit engine
• Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)
• SQLite for structured data storage
• Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
• GSM Telephony (hardware dependent)
• Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
• Camera, GPS, compass, and accelerometer (hardware dependent)
• Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE.

Android is a software stack for mobile devices that includes an operating system, middleware and key applications. This early look at the Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.
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.

Q: What is needed to make a multiple choice list with a custom view for each row?
A: Multiple choice list can be viewed by making the CheckBox android:id value be “@android:id /text1". That is the ID used by Android for the CheckedTextView in simple_list_item_multiple_choice.

Q: What dialog boxes are supported in android?Android supports 4 dialog boxes:

A:

• AlertDialog: An alert dialog box supports 0 to 3 buttons and a list of selectable elements, including check boxes and radio buttons. Among the other dialog boxes, the most suggested dialog box is the alert dialog box.
• ProgressDialog: This dialog box displays a progress wheel or a progress bar. It is an extension of AlertDialog and supports adding buttons.
• DatePickerDialog: This dialog box is used for selecting a date by the user.
• TimePickerDialog: This dialog box is used for selecting time by the user.