60+ Android App Developer Interview Questions and Answers

Activity launch modes, activity lifecycle, finding second largest number in an array, and singleton implementation.

• Activity launch modes determine how a new activity is placed in the task stack.

• Activity lifecycle consists of several states like onCreate, onStart, onResume, etc.

• To find the second largest number in an array, sort the array in descending order and return the element at index 1.

• Singleton is a design pattern that restricts the instantiation of a class to a single ...read more

Local data can be pushed to the server using APIs and network calls.

• Create an API endpoint on the server to receive the data

• Serialize the local data into a format that can be sent over the network

• Make a network call to the API endpoint with the serialized data

• Handle any errors or exceptions that may occur during the network call

Groups and View Groups are components of Android UI that help in organizing and displaying UI elements.

• View Groups are containers that hold other UI elements, such as LinearLayout, RelativeLayout, etc.

• Groups are a type of View Group that allow for the creation of complex layouts by grouping multiple UI elements together, such as RadioGroup, TableLayout, etc.

• Both Groups and View Groups are used to organize and display UI elements in a structured manner.

I am expecting a competitive stipend based on my skills, experience, and the market standards.

• I have researched the market rates for Android Application Developers and have a fair idea of the average stipend.

• I have considered my skills, experience, and qualifications while determining my expected stipend.

• I am open to negotiation and would like to discuss the compensation package in detail.

• I believe that a fair and competitive stipend will motivate me to perform at my best and...read more

Android application development concepts include activities, intents, layouts, fragments, services, and content providers.

• Activities: Represent the UI and handle user interactions.

• Intents: Enable communication between components.

• Layouts: Define the structure and appearance of UI elements.

• Fragments: Modular UI components for better UI design and reusability.

• Services: Perform background tasks independently of UI.

• Content Providers: Manage shared data between applications.

To compare list data with given data, use loops and conditional statements.

• Iterate through the list using a loop

• For each item in the list, compare it with the given data using conditional statements

• If a match is found, return true or perform the desired action

• If no match is found, return false or perform the desired action

Identify test cases for a provided Java function to evaluate its behavior with various inputs.

• Test with null input: e.g., function(null) should handle gracefully.

• Test with empty array: e.g., function([]) should return expected output.

• Test with single element: e.g., function([5]) should return the element itself.

• Test with multiple elements: e.g., function([1, 2, 3]) should return the correct processed result.

• Test with negative numbers: e.g., function([-1, -2, -3]) should handl...read more

Abstract class is a class that can have both abstract and non-abstract methods while interface only has abstract methods.

• Abstract class can have constructors while interface cannot

• A class can implement multiple interfaces but can only inherit from one abstract class

• Abstract class can have instance variables while interface cannot

• Abstract class can provide default implementation for some methods while interface cannot

• Example of abstract class: Animal (with abstract method 'mak...read more

Adaptability

• Ability to quickly learn and adapt to new technologies

• Flexibility to pivot and adjust to changing project requirements

• Openness to feedback and willingness to make improvements

• Example: Successfully transitioning from Java to Kotlin for Android development

Android architecture features include Linux kernel, libraries, runtime, application framework, and apps.

• Linux kernel provides hardware abstraction layer

• Libraries include SQLite, OpenGL, and SSL

• Runtime includes Dalvik or ART virtual machine

• Application framework provides building blocks for app development

• Apps are the end-user applications

• Modularity and flexibility are key features

MVVM is an architectural pattern that separates the user interface from the business logic and data.

• MVVM stands for Model-View-ViewModel.

• Model represents the data and business logic.

• View is the user interface that displays the data.

• ViewModel acts as a mediator between the Model and View, handling user interactions and updating the Model.

• MVVM helps in separating concerns, making code more modular and easier to maintain.

• Popular in Android development using frameworks like LiveD...read more

I got to know about Tonetag through a friend who works in the mobile app development industry.

• A friend who works in the mobile app development industry told me about Tonetag.

• I attended a tech conference where Tonetag was mentioned and got interested in learning more about it.

• I came across an article online that featured Tonetag and its innovative payment solutions.

• I saw a job posting for an Android Application Developer at Tonetag and decided to research the company.

• I joined ...read more

To increase app performance, I would use techniques like code optimization, caching, multithreading, and reducing network calls.

• Optimize code by removing unnecessary operations and improving algorithms

• Implement caching to store frequently accessed data locally

• Utilize multithreading to perform time-consuming tasks in the background

• Reduce network calls by batching requests or using local storage

• Use tools like Android Profiler to identify performance bottlenecks

API is a general term for any interface that allows communication between different software systems, while REST API is a specific type of API that uses HTTP requests to access and manipulate data.

• API stands for Application Programming Interface and is a general term for any interface that allows communication between different software systems

• REST API is a specific type of API that uses HTTP requests to access and manipulate data

• REST API is based on the principles of Represe...read more

Reverse items in array with highest values, skipping the lowest

• Sort the array in descending order

• Skip the lowest value(s)

• Reverse the remaining items

React Native is a viable option for Android app development.

• React Native allows for faster development and easier maintenance.

• It offers cross-platform compatibility and a large community for support.

• However, it may not be suitable for all types of apps and may require additional setup.

• Ultimately, the decision to use React Native or native Android development depends on the specific project requirements and resources available.

Implementing audio/video calling and live chatting using sockets involves real-time communication protocols and efficient data handling.

• Use WebRTC for real-time audio/video communication, which handles NAT traversal and provides low-latency streaming.

• For live chatting, implement TCP sockets for reliable message delivery, ensuring messages are received in order.

• Utilize libraries like Socket.IO for easier WebSocket management, enabling real-time bi-directional communication.

• Con...read more

Oops stands for Object-Oriented Programming. Abstraction is the concept of hiding implementation details. Interface defines a contract for classes to implement. Exception handling is the process of handling errors. SQL queries are used to interact with databases.

• Oops stands for Object-Oriented Programming

• Abstraction is the concept of hiding implementation details

• Interface defines a contract for classes to implement

• Exception handling is the process of handling errors

• SQL querie...read more

The life cycle of an activity and fragment in Android determines how they are created, started, resumed, paused, stopped, and destroyed.

• Activity life cycle: onCreate(), onStart(), onResume(), onPause(), onStop(), onDestroy()

• Fragment life cycle: onAttach(), onCreate(), onCreateView(), onActivityCreated(), onStart(), onResume(), onPause(), onStop(), onDestroyView(), onDestroy(), onDetach()

• Activity and fragment life cycles can be used to manage the state and behavior of the UI c...read more

Val is immutable and var is mutable in Kotlin programming language.

• Val is used to declare a variable whose value cannot be changed once assigned.

• Var is used to declare a variable whose value can be changed.

• Val is similar to final variable in Java.

• Var is similar to non-final variable in Java.

• Val is preferred over var as it ensures immutability and reduces the chances of bugs.

• Example: val name = "John" // value cannot be changed later, var age = 25 // value can be changed later

Retrofit is a type-safe HTTP client for Android and Java.

• Retrofit is used to make network requests to an API

• It converts the API response into Java objects

• To integrate an API, create an interface with the API endpoints

• Use annotations to specify the HTTP method, URL, and request parameters

• Create a Retrofit instance with the base URL and add a converter factory

• Call the API using the interface and handle the response

Scoped functions in Kotlin are functions that allow you to operate on an object within a specific scope.

• Scoped functions include 'let', 'run', 'with', 'apply', and 'also'.

• They can be used to simplify code by avoiding repetitive object references.

• Each scoped function has a specific use case, such as 'let' for null checks and 'apply' for object initialization.

The activity life cycle in Android refers to the sequence of events that occur when an activity is created, paused, resumed, and destroyed.

• Activities have different states such as onCreate, onStart, onResume, onPause, onStop, and onDestroy.

• The activity transitions between these states based on user interactions and system events.

• For example, when an activity is first created, the onCreate method is called, followed by onStart and onResume.

• When the activity is no longer visibl...read more

Android is an operating system for mobile devices developed by Google.

• Android provides a platform for developers to create mobile applications.

• It offers a wide range of features and tools for developers to build innovative apps.

• Android is used by millions of people worldwide and is constantly evolving with new updates and versions.

• It supports various programming languages such as Java, Kotlin, and C++.

• Android has a vast app store, Google Play, where users can download and ins...read more

Java interface defines a contract for classes to implement, while abstract class provides common functionality for subclasses.

• Interface can only have abstract methods, while abstract class can have both abstract and non-abstract methods.

• A class can implement multiple interfaces but can only extend one abstract class.

• Interfaces are used to achieve multiple inheritance in Java, while abstract classes are used to provide a common base for subclasses.

• Interfaces are implicitly abs...read more

Different ways to store data in Android include SharedPreferences, SQLite database, Content Providers, and File system.

• SharedPreferences: used to store key-value pairs

• SQLite database: used for structured data storage

• Content Providers: used for sharing data between applications

• File system: used for storing files locally

Kotlin scope functions are functions that allow concise code block execution on an object.

• Kotlin scope functions include let, run, with, apply, and also.

• They are used to simplify code and avoid repetitive variable references.

• For example, 'with' can be used to execute multiple operations on an object without repeating its name.

• Similarly, 'apply' can be used to initialize an object's properties without repeating its name.

• Each function has a specific use case and can be chosen b...read more