400+ Android Developer Interview Questions and Answers

Create a BSTIterator class for inorder traversal of a binary search tree.

• Implement a constructor that takes the root of the binary search tree and initializes the iterator.

• Implement next() function to return the next smallest element in the inorder traversal.

• Implement hasNext() function to check if there is a next element in the inorder traversal.

• Traverse the binary search tree in inorder to get the desired output.

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

The problem involves finding the number of ways to express a given positive integer as a sum of cubes of two integers.

• Iterate through all possible values of A and B within the given constraints.

• Check if A^3 + B^3 equals the given N, increment the count if true.

• Handle the case where A = B separately to avoid counting duplicates.

Find the majority element in an array, return -1 if no majority element is present.

• Iterate through the array and keep track of the count of each element using a hashmap.

• Check if any element's count is greater than floor(N / 2) and return it as the majority element.

• If no majority element is found, return -1.

Find the row with the maximum number of 1's in a sorted 2D matrix.

• Iterate through each row of the matrix and count the number of 1's in each row.

• Keep track of the row index with the maximum number of 1's encountered so far.

• Return the index of the row with the maximum number of 1's.

Given a string of consecutive nonnegative integers without separators, find the missing integer.

• Iterate through all possible splits of the string and check if the sequence is valid

• If the sequence is valid, return the missing integer

• Handle cases where there are multiple missing integers or the string is invalid

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.

• Implement a doubly linked list to keep track of the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access and update.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Update the order of keys in the linked list whenever a key is accessed or updated.

Convert an integer to its corresponding Roman numeral representation.

• Create a mapping of integer values to Roman numeral symbols.

• Iterate through the mapping in descending order of values and build the Roman numeral representation.

• Subtract the largest possible value from the integer at each step and append the corresponding Roman numeral symbol.

• Repeat until the integer becomes 0.

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

Check if a permutation of a string can form a palindrome.

• Create a frequency map of characters in the string.

• Check if at most one character has an odd frequency.

• If yes, return True; otherwise, return False.

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

A waste management app to track and manage waste disposal

• Include features for users to log types of waste disposed

• Implement a map feature to locate nearby waste disposal facilities

• Allow users to set reminders for waste collection days

• Incorporate a reward system for eco-friendly waste disposal practices

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

Use a Handler or AsyncTask to pass a Java object between threads.

• Use a Handler to send messages containing the object from one thread to another.

• Use AsyncTask to perform background tasks and update UI with the object on the main thread.

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

Use a thread pool to handle parallel API calls efficiently.

• Implement a thread pool to manage multiple threads for downloading images concurrently.

• Use a caching mechanism to store downloaded images and avoid redundant API calls.

• Consider using a priority queue to prioritize important images for download.

• Implement a mechanism to cancel or pause ongoing downloads if needed.

• Optimize network requests by batching multiple requests together.

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.

Different launch modes for activities in Android control how the activity is launched and how it interacts with the existing activities in the back stack.

• Standard: The default launch mode where a new instance of the activity is created every time it is launched.

• SingleTop: If the activity is already at the top of the back stack, it will not be recreated and onNewIntent() will be called instead.

• SingleTask: The activity will have a unique instance in the back stack, and if it is...read more

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.

Inter-Process Communication (IPC) mechanisms in Android OS allow different processes to communicate with each other.

• Binder: High-performance mechanism for IPC between processes in Android. Used for communication between system services and applications.

• Intent: Used for communication between components within the same application or between different applications.

• Content Providers: Allow different applications to share data through a common interface.

• Broadcast Receivers: Used ...read more

Deep links are URLs that take users directly to specific content within an app, while app links are URLs that open an app if it's installed, or redirect to a website if not.

• Deep links are used to navigate users to a specific location within an app, bypassing the home screen.

• App links are URLs that can open an app if it's installed on the device, or redirect to a website if the app is not installed.

• Deep links require specific handling in the app to properly navigate to the des...read more

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

Dependency Injection is a design pattern where components are given their dependencies rather than creating them.

• Hilt is a dependency injection library for Android that simplifies the implementation of DI in Android apps.

• Hilt generates the necessary classes for DI at compile time, reducing boilerplate code.

• Hilt provides annotations like @HiltAndroidApp, @AndroidEntryPoint, and @Inject to facilitate DI in Android development.

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

To know what things people want from a phone, conduct market research, analyze user feedback, track industry trends, and consider user demographics.

• Conduct market research to understand consumer preferences

• Analyze user feedback from reviews, surveys, and forums

• Track industry trends and technological advancements

• Consider user demographics and their specific needs

• Examples: larger battery life, better camera quality, faster performance

Constraint layout is preferred for its flexibility and efficiency.

• Allows for complex layouts with minimal nesting

• Supports responsive design and animations

• Reduces the need for nested layouts

• Improves performance by reducing layout hierarchy

• Easier to maintain and update layouts

• Compatible with Android Studio's Layout Editor

Constraint layout is more flexible and efficient than relative layout.

• Constraint layout allows for complex layouts with fewer nested views.

• It uses constraints to position and size views relative to other views or parent layout.

• Relative layout positions views relative to each other or parent layout using attributes like 'above', 'below', etc.

• Constraint layout is recommended for complex layouts with many views.

• Relative layout is recommended for simple layouts with few views.

The project can be shared with the client through various methods such as email, cloud storage, or version control systems.

• Create a build of the project

• Upload the build to a cloud storage service such as Dropbox or Google Drive

• Share the link to the build with the client

• Use a version control system such as Git to share the project with the client

• Provide instructions on how to build and run the project

The view is attached to the Fragment during the onAttach() lifecycle event.

• The onAttach() method is called when the Fragment is associated with its host Activity.

• This is the first lifecycle method called after the Fragment is created.

• The onAttach() method receives the Activity as a parameter, allowing the Fragment to interact with its host.