500+ 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.

Rearrange the nodes of a singly linked list in a specific order without altering the data of the nodes.

• Use two pointers to split the linked list into two halves.

• Reverse the second half of the linked list.

• Merge the two halves alternately to rearrange the nodes.

• Ensure to handle cases with odd and even number of nodes separately.

• Example: For input 1 -> 2 -> 3 -> 4 -> 5, the output should be 1 -> 5 -> 2 -> 4 -> 3.

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 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

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.

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

Check if any permutation of a string can form a palindrome by analyzing character frequencies.

• A palindrome reads the same forwards and backwards (e.g., 'racecar').

• For a string to have a permutation that is a palindrome, at most one character can have an odd frequency.

• Example: 'civic' -> all characters have even counts except 'v' (1), so it can form a palindrome.

• Example: 'ivicc' -> 'i' and 'c' appear twice, 'v' appears once, so it can form a palindrome.

• Example: 'hello' -> 'h',...read more

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.

Implement a local storage mechanism to cache user credentials and auto-login when internet is available.

• Use SharedPreferences to store user credentials securely.

• Implement a BroadcastReceiver to listen for network connectivity changes.

• On successful form submission, save credentials in SharedPreferences if no internet is available.

• When internet connectivity is restored, retrieve credentials and perform login automatically.

• Consider using WorkManager for background tasks to handl...read more

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

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.