50+ 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.

One way to store multiple data in mobile without using SQLite is by using SharedPreferences.

• SharedPreferences can be used to store key-value pairs of data.

• It is a lightweight storage option and is easy to implement.

• Data can be stored as primitive types, strings, or sets.

• Example: Storing user preferences, app settings, or small amounts of data.

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

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

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

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.

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

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

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

Yes, I have worked on MVVM architecture pattern.

• MVVM stands for Model-View-ViewModel.

• It separates the UI logic from the business logic.

• ViewModel acts as a mediator between Model and View.

• Data binding is a key feature of MVVM.

• I have implemented MVVM in my previous Android projects using Android Architecture Components such as LiveData and ViewModel.

Broadcast Receiver is a component of Android system that listens to system-wide broadcast announcements.

• It is used to respond to system-wide broadcast announcements.

• It is implemented as a subclass of BroadcastReceiver class.

• It can be registered either statically in AndroidManifest.xml or dynamically in code.

• Examples of system-wide broadcasts are battery low, network connectivity changes, etc.

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

I have used Android Studio, Git, JIRA, and Slack for coding in my last projects.

• Android Studio for development

• Git for version control

• JIRA for project management

• Slack for team communication

AAPT stands for Android Asset Packaging Tool. It is used to package and compile Android app resources.

• AAPT is a command-line tool that is included in the Android SDK.

• It is used to compile resources such as images, layouts, and strings into a binary format that can be used by the Android system.

• AAPT also generates the R.java file, which contains references to all the resources in an Android app.

• It can be used to package an app's resources into an APK file for distribution.

• AAPT...read more

RxJava is a library for composing asynchronous and event-based programs using observable sequences.

• RxJava is a Java implementation of ReactiveX, a library for composing asynchronous and event-based programs using observable sequences.

• It provides a set of operators to transform, filter, and combine these sequences.

• RxJava can be used for network calls, database operations, UI events, and more.

• It simplifies concurrency and makes code more readable and maintainable.

• Example: Obser...read more

Java is an object-oriented programming language while C++ is a hybrid language that supports both procedural and object-oriented programming.

• Java is platform-independent while C++ is platform-dependent.

• Java has automatic garbage collection while C++ requires manual memory management.

• Java has a simpler syntax compared to C++.

• Java does not support pointers while C++ does.

• Java has a built-in exception handling mechanism while C++ requires manual exception handling.

• Java is used f...read more

The output of a left join operation.

• A left join returns all the rows from the left table and the matching rows from the right table.

• If there is no match, NULL values are returned for the right table columns.

• The output will have all the columns from the left table and the matching columns from the right table.

Working with school requires communication, planning, and flexibility.

• Establish clear communication channels with school staff

• Plan ahead for deadlines and events

• Be flexible and adaptable to changes in schedule or curriculum

• Collaborate with teachers and administrators to support student success

Perfect singleton design pattern ensures only one instance of a class is created and provides a global point of access to it.

• Private constructor to prevent direct instantiation

• Private static instance variable

• Public static method to access the instance

• Lazy initialization to create the instance only when needed

• Thread-safe implementation to prevent multiple instances in a multi-threaded environment

Work Manager is an Android Jetpack library used for managing deferrable, asynchronous tasks.

• Work Manager is part of the Android Jetpack library.

• It is used for managing deferrable, asynchronous tasks that need to run even if the app is in the background.

• Work Manager provides various constraints and options for scheduling tasks, such as network availability, charging status, and more.

• It is recommended for tasks that are not time-critical and can be deferred to run at a later ti...read more

Use a loop to search for a specific string in an array of strings.

• Iterate through each string in the array

• Use a conditional statement to check if the current string matches the search string

• Return the index of the matching string or -1 if not found

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

• Android is based on the Linux kernel.

• It provides a framework for building mobile applications.

• Android applications are written in Java or Kotlin programming languages.

• Android supports a wide range of hardware devices and screen sizes.

• Google Play Store is the official app store for Android applications.

An Android developer should have knowledge of Java, Android SDK, and experience in developing mobile applications.

• Proficiency in Java programming language

• Familiarity with Android SDK and Android Studio

• Experience in developing mobile applications

• Knowledge of RESTful APIs and JSON

• Understanding of Material Design guidelines

• Ability to work with third-party libraries and APIs

• Debugging and problem-solving skills

• Knowledge of version control systems like Git

MVVM is a design pattern that separates UI code from business logic and data handling.

• MVVM stands for Model-View-ViewModel

• Model represents the data and business logic

• View displays the UI and user interactions

• ViewModel acts as a mediator between Model and View

• ViewModel exposes data and commands to the View

• Data binding is used to keep the View and ViewModel in sync

• MVVM promotes testability and maintainability of code

The life cycle of an Android activity refers to the different states an activity goes through during its lifetime.

• onCreate() is called when the activity is first created

• onStart() is called when the activity becomes visible to the user

• onResume() is called when the activity starts interacting with the user

• onPause() is called when the activity is partially obscured by another activity

• onStop() is called when the activity is no longer visible to the user

• onDestroy() is called when ...read more

Context is an object that provides access to application-specific resources and classes.

• Context is used to access resources like databases, preferences, etc.

• It is required for creating views, starting activities, and accessing system services.

• Examples include accessing strings from resources, launching activities, and creating intents.

Java threads allow concurrent execution of multiple parts of a program.

• Threads are created by extending the Thread class or implementing the Runnable interface

• Threads can be started using the start() method

• Thread.sleep() can be used to pause a thread for a specified amount of time

• Synchronization can be used to prevent multiple threads from accessing shared resources simultaneously

Intent is a messaging object used to request an action from another app component.

• Intent is used to start activities, services, and broadcast receivers in Android.

• It can also be used to pass data between components.

• There are two types of intents: explicit intents and implicit intents.

• Explicit intents specify the component to start by name.

• Implicit intents specify the action to perform and let the system find the appropriate component to handle it.

MVC (Model-View-Controller) architecture design pattern separates an application into three main components.

• Model: Represents the data and business logic of the application

• View: Represents the UI components of the application

• Controller: Acts as an intermediary between Model and View, handling user input and updating the Model accordingly

Activity life cycle refers to the stages an activity goes through from creation to destruction.

• An activity is created using onCreate() method

• It becomes visible using onStart() method

• It becomes interactive using onResume() method

• It goes to background using onPause() method

• It becomes invisible using onStop() method

• It gets destroyed using onDestroy() method

OOPs is a programming paradigm that uses objects to represent real-world entities and their interactions.

• OOPs stands for Object-Oriented Programming.

• It is based on the concept of classes and objects.

• Encapsulation, inheritance, and polymorphism are the three main pillars of OOPs.

• Encapsulation is the process of hiding the implementation details of an object from the outside world.

• Inheritance allows a class to inherit properties and methods from another class.

• Polymorphism allows...read more

Stock span problem is a financial problem where we have a series of n daily price quotes for a stock and we need to calculate the span of stock's price for all n days.

• Use a stack to keep track of the previous days' prices and their spans.

• For each day, pop the stack until a price greater than the current day's price is found, then calculate the span.

• Push the current day's price and span onto the stack.

MVVM is a design pattern used in Android development to separate the UI logic from the business logic.

• MVVM stands for Model-View-ViewModel

• Model represents the data and business logic

• View is the UI component that displays the data

• ViewModel acts as a mediator between the Model and View, handling the UI logic and data manipulation

• MVVM helps in maintaining a clean and organized codebase

Various types of errors include syntax errors, logical errors, and runtime errors.

• Syntax errors occur when code violates the rules of the programming language.

• Logical errors occur when code does not produce the expected output due to flawed logic.

• Runtime errors occur when code encounters an unexpected condition during execution.

• Other types of errors include semantic errors, input/output errors, and network errors.

LazyRow is a Jetpack Compose component for displaying horizontally scrolling lists, while RecyclerView is a traditional Android view for displaying large data sets efficiently.

• LazyRow is part of Jetpack Compose, RecyclerView is part of the Android framework

• LazyRow is more declarative and easier to use for simple lists, RecyclerView is more powerful and customizable for complex lists

• LazyRow automatically handles recycling of items, RecyclerView requires manual implementation o...read more