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Android Interview Questions and Answers

Test your skills through the online practice test: Android Quiz Online Practice Test

Freshers / Beginner level questions & answers

Ques 1. What is Android?

Android is a complete set of software for mobile devices such as tablet computers, notebooks, smartphones, electronic book readers, set-top boxes etc.

It contains a linux-based Operating System, middleware and key mobile applications.

It can be thought of as a mobile operating system. But it is not limited to mobile only. It is currently used in various devices such as mobiles, tablets, televisions etc.

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Ques 2. Who has developed Android?

It is developed by Google and later the OHA (Open Handset Alliance). Java language is mainly used to write the android code even though other languages can be used.

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Ques 3. What is Open Handset Alliance (OHA)?

It's a consortium of 84 companies such as google, samsung, AKM, synaptics, KDDI, Garmin, Teleca, Ebay, Intel etc.

It was established on 5th November, 2007, led by Google. It is commited to advance open standards, provide services and deploy handsets using the Android Plateform.

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Ques 4. What are the features/advantages of Android?

Advantages of android follows:
  • It is open-source.
  • Anyone can customize the Android Platform.
  • There are a lot of mobile applications that can be chosen by the consumer.
  • It provides many interesting features like weather details, opening screen, live RSS (Really Simple Syndication) feeds etc.
  • It provides support for messaging services(SMS and MMS), web browser, storage (SQLite), connectivity (GSM, CDMA, Blue Tooth, Wi-Fi etc.), media, handset layout etc.

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Ques 5. What are the categories of Android applications?

There are many android applications in the market. The top categories are:
  • Entertainment
  • Communication
  • Tools
  • Productivity
  • Music and Audio
  • Social
  • Media and Video
  • Personalization
  • Travel and Local etc.

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Ques 6. What is the history of Android?

The history and versions of android is very interesting. The codenames of android ranges from A to J currently, such as Aestro, Blender, Cupcake, Donut, Eclair, Froyo, Gingerbread, Honeycomb, Ice Cream Sandwitch,Jelly Bean and KitKat. 
Let's understand the android history pointly:
Initially, Andy Rubin founded Android Incorporation in Palo Alto, California, United States in October, 2003.
In 17th August 2005, Google acquired android Incorporation. Since then, it is in the subsidiary of Google Incorporation.
The key employees of Android Incorporation are Andy Rubin, Rich Miner, Chris White and Nick Sears.

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Ques 7. Describe Android Software Stack.

Android software stack (also known as android architecture) includes linux kernal, native libraries (middleware), Android Runtime, Application Framework and Applications.
Linux Kernal is responsible for device drivers, power management, resource access etc. OS tasks.
On the top of linux kernal, their are Native libraries such as WebKit, OpenGL, FreeType, SQLite, Media, C runtime library (libc) etc.
The WebKit library is responsible for browser support, SQLite is for database, FreeType for font support, Media for playing and recording audio and video formats.
The main Android API's are UI (User Interface), telephony, resources, locations, Content Providers (data) and package managers.

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Ques 8. Describe Android Core Building Blocks.

A component is simply a piece of code that has a well defined life cycle e.g. Activity, Receiver, Service etc.
The core building blocks or fundamental components of android are activities, views, intents, services, content providers, fragments and AndroidManifest.xml.

Activity
An activity is a class that represents a single screen. It is like a Frame in AWT.

View
A view is the UI element such as button, label, text field etc. Anything that you see is a view.

Intent
Intent is used to invoke components. It is mainly used to:
Start the service
Launch an activity
Display a web page
Display a list of contacts
Broadcast a message
Dial a phone call etc.

Service
Service is a background process that can run for a long time.
There are two types of services local and remote. Local service is accessed from within the application whereas remote service is accessed remotely from other applications running on the same device.

Content Provider
Content Providers are used to share data between the applications.

Fragment
Fragments are like parts of activity. An activity can display one or more fragments on the screen at the same time.

AndroidManifest.xml
It contains informations about acvities, content providers, permissions etc. It is like the web.xml file in Java EE.

Android Virtual Device (AVD)
It is used to test the android application without the need for mobile or tablet etc. It can be created in different configurations to emulate different types of real devices.

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Ques 9. What is Android Emulator?

Android Emulator is used to run, debug and test the android application. If you don't have the real device, it can be the best way to run, debug and test the application.
It uses an open source processor emulator technology called QEMU.

The emulator tool enables you to start the emulator from the command line. You need to write:
emulator -avd <AVD NAME>

In case of Eclipse IDE, you can create AVD by Window menu > AVD Manager > New.

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Ques 10. How to create/make android apps?

We are creating the simple example of android using the Eclipse IDE. For creating the simple example:
1) Create the new android project
2) Write the message (optional)
3) Run the android application

1) For creating the new android project:
Select File > New > Project...
Select the android project and click next
Fill the Details in this diaglog box and click finish
Now an android project have been created. You can explore the android project and see the simple program.
2) For writing the message we are using the TextView class. Change the onCreate method as:
package com.example.helloandroid;  
  
import android.os.Bundle;  
import android.app.Activity;  
import android.view.Menu;  
import android.widget.TextView;  
  
public class MainActivity extends Activity {  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
          
        TextView textview=new TextView(this);  
        textview.setText("Hello Android!");  
          
        setContentView(textview);  
    }  
  
    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {  
        // Inflate the menu; this adds items to the action bar if it is present.  
        getMenuInflater().inflate(R.menu.activity_main, menu);  
        return true;  
    }  
      
}  

3) To run the android application:
Right click on your project > Run As.. > Android Application
The android emulator might take 2 or 3 minutes to boot. So please have patience. After booting the emulator, the eclipse plugin installs the application and launches the activity. You will see something like this:

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Ques 11. Describe Internal details of previous Hello Android application.

Here, we are going to learn the details of first android program.

Android application contains different components such as java source code, string resources, images, manifest file, apk file etc. Let's understand the project structure of android application.

MainActivity.java - Java Source
R.java in generated package - Generated R.java
bin folder - Contains apk file
drawable, activity_main.xml, strings.xml - Resources
AndroidManifest.xml - Manifest

Let's see the java source file created by the Eclipse IDE:
File: MainActivity.java
package com.example.helloandroid;  
  
import android.os.Bundle;  
import android.app.Activity;  
import android.view.Menu;  
import android.widget.TextView;  
  
public class MainActivity extends Activity {//(1)  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {//(2)  
        super.onCreate(savedInstanceState);  
                
        setContentView(R.layout.activity_main);//(3)  
    }  
  
    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {//(4)  
        // Inflate the menu; this adds items to the action bar if it is present.  
        getMenuInflater().inflate(R.menu.activity_main, menu);  
        return true;  
    }  
      

(1) Activity is a java class that creates and default window on the screen where we can place different components such as Button, EditText, TextView, Spinner etc. It is like the Frame of Java AWT.
It provides life cycle methods for activity such as onCreate, onStop, OnResume etc.

(2) The onCreate method is called when Activity class is first created.

(3) The setContentView(R.layout.activity_main) gives information about our layout resource. Here, our layout resources are defined in activity_main.xml file.

File: activity_main.xml
<RelativeLayout xmlns:androclass="http://schemas.android.com/apk/res/android"  
    xmlns:tools="http://schemas.android.com/tools"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    tools:context=".MainActivity" >  
  
    <TextView  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_centerHorizontal="true"  
        android:layout_centerVertical="true"  
        android:text="@string/hello_world" />  
  
</RelativeLayout>  
As you can see, a textview is created by the framework automatically. But the message for this string is defined in the strings.xml file. The @string/hello_world provides information about the textview message. The value of the attribute hello_world is defined in the strings.xml file.

File: strings.xml
<?xml version="1.0" encoding="utf-8"?>  
<resources>  
  
    <string name="app_name">helloandroid</string>  
    <string name="hello_world">Hello world!</string>  
    <string name="menu_settings">Settings</string>  
  
</resources>  
You can change the value of the hello_world attribute from this file.

Generated R.java file
It is the auto-generated file that contains IDs for all the resources of res directory. It is generated by aapt(Android Asset Packaging Tool). Whenever you create any component on activity_main, a corresponding ID is created in the R.java file which can be used in the Java Source file later.

File: R.java
/* AUTO-GENERATED FILE.  DO NOT MODIFY. 
 * 
 * This class was automatically generated by the 
 * aapt tool from the resource data it found.  It 
 * should not be modified by hand. 
 */  
  
package com.example.helloandroid;  
public final class R {  
    public static final class attr {  
    }  
    public static final class drawable {  
        public static final int ic_launcher=0x7f020000;  
    }  
    public static final class id {  
        public static final int menu_settings=0x7f070000;  
    }  
    public static final class layout {  
        public static final int activity_main=0x7f030000;  
    }  
    public static final class menu {  
        public static final int activity_main=0x7f060000;  
    }  
    public static final class string {  
        public static final int app_name=0x7f040000;  
        public static final int hello_world=0x7f040001;  
        public static final int menu_settings=0x7f040002;  
    }  
    public static final class style {  
        /**  
        Base application theme, dependent on API level. This theme is replaced 
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices. 
     
 
            Theme customizations available in newer API levels can go in 
            res/values-vXX/styles.xml, while customizations related to 
            backward-compatibility can go here. 
         
 
        Base application theme for API 11+. This theme completely replaces 
        AppBaseTheme from res/values/styles.xml on API 11+ devices. 
     
 API 11 theme customizations can go here.  
 
        Base application theme for API 14+. This theme completely replaces 
        AppBaseTheme from BOTH res/values/styles.xml and 
        res/values-v11/styles.xml on API 14+ devices. 
     
 API 14 theme customizations can go here.  
         */  
        public static final int AppBaseTheme=0x7f050000;  
        /**  Application theme.  
 All customizations that are NOT specific to a particular API-level can go here.  
         */  
        public static final int AppTheme=0x7f050001;  
    }  
}  

APK File
An apk file is created by the framework automatically. If you want to run the android application on the mobile, transfer and install it.

Resources
It contains resource files including activity_main, strings, styles etc.

Manifest file
It contains information about package including components such as activities, services, content providers etc.

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