400+ Android Developer Interview Questions and Answers

An Android photo viewing app with a list of images from disk, one taking half the screen.

• Use RecyclerView to display the list of images

• Use a custom adapter to bind the images to the RecyclerView

• Use a GridLayoutManager with span count of 2 to achieve the half-screen effect

• Load images from disk using a library like Glide or Picasso

• Implement click listeners to handle item selection and display the selected image

Design a screen to show 10 nearest restaurants in a list with uninterrupted scrolling.

• Use a RecyclerView to display the list of restaurants

• Implement a custom adapter to populate the data in the list

• Use a location service to get the user's current location

• Sort the restaurants based on their distance from the user's location

• Load more restaurants as the user scrolls to the end of the list

Android components include activities and fragments, each with their own lifecycle methods. Transitioning from one activity to another triggers specific lifecycle methods in each screen.

• Android components include activities and fragments

• Activity lifecycle methods: onCreate(), onStart(), onResume(), onPause(), onStop(), onDestroy()

• Fragment lifecycle methods: onAttach(), onCreate(), onCreateView(), onActivityCreated(), onStart(), onResume(), onPause(), onStop(), onDestroyView()...read more

To search for contacts with duplicate names or numbers, iterate through the list and compare each contact's name and number with the search term.

• Iterate through the list of contacts

• Compare the search term with each contact's name and number

• Return the contacts that match the search term

To transfer the Ball object from one thread to another, we can use Handler or AsyncTask.

• Use Handler to post a Runnable to the main thread's message queue

• Use AsyncTask to perform background operations and update the UI on the main thread

• Pass the Ball object as a parameter or use a shared variable between threads

Developed a social media app using Kotlin and MVVM architecture.

• Used Kotlin for coding the app

• Implemented MVVM architecture for better code organization

• Integrated Firebase for real-time database and authentication

• Used Glide library for image loading and caching

• Implemented RecyclerView for displaying posts and comments

To create my own HashMap, I would use an array of linked lists to handle collisions and implement key-value pairs using a hash function.

• Create an array of linked lists to store the key-value pairs

• Implement a hash function to generate an index for each key

• Handle collisions by adding elements to the linked list at the corresponding index

• Support operations like put(key, value), get(key), and remove(key)

Android development is the process of creating applications for the Android operating system.

• Android development involves writing code in Java or Kotlin to create mobile applications.

• It includes designing user interfaces, implementing functionality, and testing the app.

• Developers use Android Studio, an integrated development environment (IDE), for building Android apps.

• Android apps can be published on the Google Play Store and run on various devices.

• Examples of Android apps i...read more

The activity creator is used to create instances of an activity class in Android development.

• The activity creator is responsible for instantiating an activity class.

• It is typically used when starting a new activity from another activity.

• The activity creator can pass data to the new activity through intent extras.

• It is commonly used in the onCreate() method of the calling activity.

• Example: Intent intent = new Intent(this, SecondActivity.class); startActivity(intent);

Given an array of natural numbers in random order, find the first missing natural number.

• Sort the array in ascending order

• Iterate through the sorted array and compare each element with its index

• If the element is not equal to its index + 1, return the missing number

• If all elements are in order, return the next natural number after the last element

JSON parsing is the process of converting JSON data into a usable format in programming.

• JSON parsing is essential for retrieving and manipulating data from APIs or databases.

• It involves converting JSON strings into objects or arrays in programming languages like Java or Kotlin.

• Handling team conflicts involves effective communication, active listening, and finding compromises.

• Agile methodologies focus on iterative development, collaboration, and adapting to change.

• Work experie...read more

Diamond problem occurs in multiple inheritance where two superclasses have a common method.

• Java doesn't support multiple inheritance to avoid diamond problem.

• Diamond problem can be solved using interfaces.

• Example: class A and class B both have a method named 'display', class C extends A and B, now if we call display() from C, which method will be called?

• To avoid ambiguity, Java uses interfaces to achieve multiple inheritance.

Broadcast is a messaging system in Android that allows communication between different components of an app or between different apps.

• Broadcast is a way to send messages to multiple components or apps at once.

• There are two types of broadcasts: ordered and unordered.

• Ordered broadcasts are delivered to receivers in a specific order, while unordered broadcasts are delivered to all receivers at once.

• Broadcasts can be used for various purposes such as sending system events, notify...read more

Move all zeroes to left and ones to right in an array

• Iterate through the array from both ends

• Swap the elements if left is 1 and right is 0

• Stop when left and right pointers meet

Looper/handlers allow passing objects between threads in Android.

• Looper is a message loop that runs in a thread and processes messages from a message queue.

• Handlers are used to send messages to the message queue of a looper.

• When an object is passed from one thread to another using a handler, it is encapsulated in a message and added to the receiving thread's message queue.

• The receiving thread's looper then processes the message and delivers it to the handler's callback method...read more

Yes, I have experience in handling code repos and have used various third-party libraries.

• I have experience in using Git for version control and have managed code repositories on GitHub and Bitbucket.

• I have used third-party libraries such as Retrofit, OkHttp, Gson, and Picasso for network operations, JSON parsing, and image loading respectively.

• I have also used libraries like ButterKnife and Dagger for dependency injection and RxJava for reactive programming.

• I make sure to ke...read more

A weather app that displays images for different weather conditions, taking care of half downloaded images and minimizing data consumption.

• Implement image caching to store downloaded images locally

• Check if the image is already downloaded before making a network request

• Use a progress bar to indicate the download status of the image

• Handle cases where the download is interrupted or incomplete

• Implement a mechanism to resume the download from where it left off

• Optimize image loadin...read more

Marker interface is an empty interface used to mark a class as having a particular property or behavior.

• Marker interface has no methods or fields, it is used to provide metadata to the code.

• It is used to indicate that a class has a certain capability or should be treated in a special way.

• Examples of marker interfaces are Serializable, Cloneable, and Remote.

• Interfaces are used to achieve abstraction and provide a contract for implementing classes.

• Interfaces are used to achieve...read more

Fragments are reusable UI components in Android that can be used within activities. They are preferred over activities in certain scenarios.

• Fragments allow for modular and reusable UI components.

• They can be used to create multi-pane layouts for tablets and larger screens.

• Fragments can be added or removed dynamically at runtime.

• They can retain their state during configuration changes.

• Fragments can communicate with each other and with the hosting activity using interfaces.

Minimum time required to cross the bridge is 17 minutes.

• A and B cross (2 minutes), A returns (1 minute), C and D cross (10 minutes), B returns (2 minutes), A and B cross (2 minutes).

• Always send the fastest person back to minimize time.

• Total time taken is the sum of all individual crossing times.

To set equal spacing between childs of constraint layout, use the chain style property.

• Create a chain of the views that need equal spacing using the chain style property.

• Set the chain style to spread inside the constraint layout.

• Adjust the margins of the views to control the spacing.

• Use the layout_constraintHorizontal_chainStyle or layout_constraintVertical_chainStyle attribute to set the chain style.

• Example: app:layout_constraintHorizontal_chainStyle="spread"

Serializable is a marker interface that allows objects to be converted into a byte stream, while Parcelable is an Android-specific interface for efficient object serialization.

• Serializable is a standard Java interface, while Parcelable is an Android-specific interface.

• Serializable uses reflection to serialize and deserialize objects, which can be slower and less efficient.

• Parcelable requires explicit implementation of methods for serialization and deserialization, making it f...read more

I have a strong understanding of databases, including MySQL and SQL Server.

• I am proficient in writing SQL queries and managing databases.

• I have experience in designing and implementing database schemas.

• I am familiar with database optimization techniques.

• I have worked with both MySQL and SQL Server in various projects.

• I understand the differences between the two and can work with either one.

OOPS stands for Object-Oriented Programming System. It is a programming paradigm that uses objects to represent real-world entities.

• OOPS allows for modular and reusable code.

• It provides a clear structure and organization to the code.

• Encapsulation, inheritance, and polymorphism are key concepts in OOPS.

• Example: In an Android app, each screen can be represented as an object with its own properties and behaviors.

• OOPS promotes code reusability and maintainability.

To find highest count of viewers at any given point from in-out time log

• Create an array of time slots with start and end time

• Loop through the log and increment the count for each time slot

• Track the maximum count and corresponding time slot

• Return the time slot with highest count

Memory leakage can cause app crashes and slow performance. It can be avoided by proper memory management and identifying the root cause.

• Avoid creating unnecessary objects

• Release unused resources

• Use memory profiling tools like Android Profiler

• Avoid static references to objects

• Use weak references when necessary

Answering questions on abstract class vs interface and creating JDBC application for data saving.

• Abstract class can have method implementations while interface cannot

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

• JDBC application can be created by loading the driver, establishing connection, creating statement, executing query and closing connection

• Example: Class.forName("com.mysql.jdbc.Driver"); Connection con=DriverManager.getConnectio...read more

Android components like Recycler View, View Model, ANR are essential for building robust Android applications.

• Recycler View: Efficient way to display large data sets by recycling views as they scroll off the screen.

• View Model: Manages UI-related data in a lifecycle-conscious way, surviving configuration changes.

• ANR (Application Not Responding): Dialog shown to the user when the main thread of an app is blocked for too long.

• Understanding how these components work internally is...read more