Android Interview Questions & Answer

Q.1 Explain in brief about the important file and folder when you create new android application.

When you create android application the following folders are created in the package explorer in eclipse which are as follows:

src: Contains the .java source files for your project. You write the code for your application in this file. This file is available under the package name for your project.

gen: This folder contains the R.java file. It is compiler-generated file that references all the resources found in your project. You should not modify this file.

Android 4.0 library: This folder contains android.jar file, which contains all the class libraries needed for an Android application.

assets: This folder contains all the information about HTML file, text files, databases, etc.

bin: It contains the .apk file (Android Package) that is generated by the ADT during the build process. An .apk file is the application binary file. It contains everything needed to run an Android application.

res: This folder contains all the resource file that is used byandroid application. It contains subfolders as: drawable, menu, layout, and values etc.
Q.2 Explain AndroidManifest.xmlfile in detail.

<?xml version=”1.0″ encoding=”utf-8″?>
<manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”com.example.careerride” android:versionCode=”1″ android:versionName=”1.0″>

<uses-sdk android:minSdkVersion=”8″ android:targetSdkVersion=”18″ />

<application android:allowBackup=”true” android:icon=”@drawable/ic_launcher” android:label=”@string/app_name” android:theme=”@style/AppTheme”>

<activity android:name=”com.example.careerride.MainActivity” android:label=”@string/app_name”>
<intent-filter>
<action android:name=”android.intent.action.MAIN” />
<category android:name=”android.intent.category.LAUNCHER” />
</intent-filter>
</activity>
</application>

</manifest>

The AndroidManifest.xml file contains the following information about the application:

It contains the package name of the application.
The version code of the application is 1.This value is used to identify the version number of your application.
The version name of the application is 1.0
The android:minSdkVersion attribute of the element defines the minimum version of the OS on which the application will run.
ic_launcher.png is the default image that located in the drawable folders.
app_name defines the name of application and available in the strings.xml file.
It also contains the information about the activity. Its name is same as the application name.

Q.3 Describe android Activities in brief.

Activity provides the user interface. When you create an android application in eclipse through the wizard it asks you the name of the activity. Default name is MainActivity. You can provide any name according to the need. Basically it is a class (MainActivity) that is inherited automatically from Activity class. Mostly, applications have one or more activities and the main purpose of an activity is to interact with the user. Activity goes through a number of stages, known as an activity’s life cycle.

Example:

package com.example.careerride; //Application name careerride

import android.os.Bundle; // Default packages
import android.app.Activity; // Default packages
import android.view.Menu;

public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}

When you run the application onCreate method is called automatically.
Q.4 Describe Intents in detail.

An Android application can contain zero or more activities. If you want to navigate from one activity to another then android provides you Intent class. This class is available in android.content.Intent package.One of the most common uses for Intents is to start new activities.

There are two types of Intents.

Explicit Intents
Implicit Intents

Intents works in pairs: action and data. The action defines what you want to do, such as editing an item, viewing the content of an item etc. The data specifies what is affected,such as a person in the Contacts database. The data is specified as an Uri object.

Explicitly starting an Activity

Intent intent = newIntent (this, SecondActivity.class);

startActivity(intent);

Here SecondActivity is the name of the target activity that you want to start.

Implicitly starting an Activity

If you want to view a web page with the specified URL then you can use this procedure.

Intent i = newIntent(android.content.Intent.ACTION_VIEW,Uri.parse(“http://www.amazon.com”));

startActivity(i);

if you want to dial a telephone number then you can use this method by passing the telephone number in the data portion

Intent i = newIntent (android.content.Intent.ACTION_DIAL,Uri.parse(“tel:+992366…..”));

startActivity(i);

In the above method the user must press the dial button to dial the number. If you want to directly call the number without user intervention, change the action as follows:

Intent i = newIntent (android.content.Intent.ACTION_CALL,Uri.parse(“tel:+99234554…..”));

startActivity(i);

If you want to dial tel no or use internet then write these line in AndroidManifest.xml

<uses-permissionandroid:name=”android.permission.CALL_PHONE”/>
<uses-permissionandroid:name=”android.permission.INTERNET”/>
Q.5 How to send SMS in android? Explain with example.

SMS messaging is one of the basic and important applications on a mobile phone. Now days every mobile phone has SMS messaging capabilities, and nearly all users of any age know how to send and receive such messages. Mobile phones come with a built-in SMS application that enables you to send and receiveSMS messages. If you want to send the SMS programmatically then follow the following steps.

Sending SMS Messages programmatically

Take a button on activity_main.xml file as follows.

<Button android:id=”@+id/btnSendSMS” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:layout_centerHorizontal=”true” android:layout_centerVertical=”true” android:onClick=”sendmySMS” android:text=”sendSMS” />

According to above code when user clicks the button sendmySMS method will be called. sendmySMS is user defined method.

In the AndroidManifest.xml file, add the following statements

<uses-permissionandroid:name=”android.permission.SEND_SMS”/>

Now we write the final step. Write the given below method in MainActivity,java file

publicvoidsendmySMS(View v)
{
SmsManagersms = SmsManager.getDefault();
sms.sendTextMessage(“5556”, null, “Hello from careerRide”, null, null);
}
In this example I have used two emulator. On the first Android emulator (5554), click the Send SMSbutton to send an SMS message to the second emulator(5556).
Q.6 Describe the SmsManager class in android.

SmsManager class is responsible for sending SMS from one emulator to another or device.

You cannot directly instantiate this class; instead, you call the getDefault() static method to obtain an SmsManager object. You then send the SMS message using the sendTextMessage() method:

SmsManagersms = SmsManager.getDefault();

sms.sendTextMessage(“5556”, null, “Hello from careerRide”, null, null);

sendTextMessage() method takes five argument.

destinationAddress – Phone number of the recipient.
scAddress – Service center address; you can use null also.
text – Content of the SMS message that you want to send.
sentIntent – Pending intent to invoke when the message is sent.
deliveryIntent – Pending intent to invoke when the message has been delivered.

Q.7 How you can use built-in Messaging within your application?

You can use an Intent object to activate the built-in Messaging service. You have to pass MIME type “vnd.android-dir/mms-sms”, in setType method of Intent as shown in the following given below code.

Intent intent = new Intent (android.content.Intent.ACTION_VIEW);
intent.putExtra(“address”, “5556; 5558;”);// Send the message to multiple recipient.
intent.putExtra(“sms_body”, “Hello my friends!”);
intent.setType(“vnd.android-dir/mms-sms”);
startActivity(intent);

Q.8 What are different data storage options are available in Android?

Different data storage options are available in Android are:

SharedPreferences
SQlite
ContentProvider
File Storage
Cloud Storage

Q.9 Describe SharedPreference storage option with example.

SharedPreference is the simplest mechanism to store the data in android. You do not worry about creating the file or using files API.It stores the data in XML files. SharedPreference stores the data in key value pair.The SharedPreferences class allows you to save and retrieve key-value pairs of primitive data types. You can use SharedPreferences to save any primitive data: boolean, floats, int, longs, and strings.The data is stored in XML file in the directory data/data//shared-prefs folder.

Application of SharedPreference

Storing the information about number of visitors (counter).
Storing the date and time (when your Application is updated).
Storing the username and password.
Storing the user settings.

Example:

Android

For storing the data we will write the following code in main activity on save button:

SharedPreferences sf=getSharedPreferences(“MyData”, MODE_PRIVATE);
SharedPreferences.Editored= sf.edit();
ed.putString(“name”, txtusername.getText().toString());
ed.putString(“pass”, txtpassword.getText().toString());
ed.commit();

In this example I have taken two activities. The first is MainActivity and the second one is SecondActivity. When user click on save button the user name and password that you have entered in textboxes, will be stored in MyData.xml file.

Here MyData is the name of XML file .It will be created automatically for you.

MODE_PRIVATE means this file is used by your application only.

txtusername and txtpassword are two EditText control in MainActivity.

For retrieving the data we will write the following code in SecondActiviy when user click on Load button:

Public static final String DEFAULT=”N? A”;

DEFAULT is a String type user defined global variable.If the data is not saved in XML file and user click on load button then your application will not give the error. It will show message “No Data is found”. Here name and pass are same variable that I have used in MainActivity.

SharedPreferences sf=getSharedPreferences(“MyData”, Context.MODE_PRIVATE);

String Uname=sf.getString(“name”, DEFAULT);

String UPass=sf.getString(“pass”, DEFAULT);

if(name.equals(DEFAULT)||Pass.equals(DEFAULT))
{
Toast.makeText(this, “No data is found”, Toast.LENGTH_LONG).show();
}

else

{

Txtusername.setText(Uname);
Txtpassword.setText(UPass) ;
}
Q.10 What are the key components of Android Architecture?

Android Architecture consists of 4 key components:
– Linux Kernel
– Libraries
– Android Framework
– Android Applications
Q.11 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
Q.12 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.
Q.13 What do you know about Intents?

– Notification messages to the user from an Android enabled device can be displayed using Intents. The users can respond to intents.
– There are two types of Intents – Explicit Intent, Implicit Intent.
Q.14 What is an Explicit Intent?

– Explicit intent specifies the particular activity that should respond to the intent.
– They are used for application internal messages.
Q.15 What is an Implicit Intent?

– In case of Implicit Intent, an intent is just declared.
– It is for the platform to find an activity that can respond to it.
– Since the target component is not declared, it is used for activating components of other applications.
Q.16 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.
Q.17 Where are lay out details placed? Why?

– Layout details are placed in XML files
– XML-based layouts provide a consistent and standard means of setting GUI definition format.
Q.18 What do containers hold?

– Containers hold objects and widgets in a specified arrangement.
– They can also hold labels, fields, buttons, or child containers. .
Q.19 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
Q.20 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.
Q.21 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.
Q.22 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
Q.23 Tell us something about nine-patch image.

– The Nine-patch in the image name refers to the way the image can be resized: 4 corners that are unscaled, 4 edges that are scaled in 1 axis, and the middle one that can be scaled into both axes.
– A Nine-patch image allows resizing that can be used as background or other image size requirements for the target device.
Q.24 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.
Q.25 What is Dalvik Virtual Machine?

– It is Android’s virtual machine.
– It is an interpreter-only virtual machine which executes files in Dalvik Executable (.dex) format. This format is optimized for efficient storage and memory-mappable execution.

Q.26 How to avoid ANR status?

Android allows the system to protect the applications that are not responsive for a period of time by displaying a status called as ANR (Application not responding). Methods should use the main thread for work, as it takes long time for the main thread to complete the task. The work should be divided and another thread named as child thread be used for executing more tasks, as it takes less time. Main thread should provide a handler for child threads to post back upon completion.

Q.27 How does the AOSP relate to the Android Compatibility Program?

AOSP stands for Android Open-source project that maintains Android software and keep track of the new versions. It can be used for any purpose including the devices that are not compatible with other devices. It is related to the Android Compatibility Program as it defines the implementation of Android that is compatible with the third party apps.

Q.28 What is localization and how to achieve?

Localization is a way of representing the products in different languages. Android is an operating system which runs in many regions, so to reach different users localization is a must. Localization in Android can be achieved by incorporating different languages in the application which you are using. To do this knowledge of Java,XML elements, Activity lifecycle and general principles of internationalization and localization are required.

Q.29 What is a Sticky Intent?

Intent is basically an abstract description of an operation that has to be performed for communication. Sticky Intent is also a type of intent which allows the communication between a function and a service. For example: sendStickyBroadcast() performs send Broadcast(Intent) which stays even after the broadcast is complete. It helps in retrieving the data quickly. The message ACTION_BATTERY_CHANGED of an operating system is an example of it.

Q.30 How to Translate in Android?

Android uses Google translator to translate data from one language into another language using XAMPP. XAMPP is used to transmit the data. The steps which have to be followed are: Type the message in your language, go to the language setting, a list will be displayed there, select the language from the list to convert your text.