60+ Backend Developer Interview Questions and Answers for Freshers

Sort an array of 0's, 1's, and 2's using two pointer approach.

• Initialize two pointers, one at the beginning and one at the end of the array.

• Traverse the array and swap 0's to the beginning and 2's to the end using the pointers.

• Stop when the pointers meet or cross each other.

Search for an element in a rotated sorted array using binary search with pivot.

• Find the pivot element using binary search.

• Compare the target element with the first element of the array to determine which half to search.

• Perform binary search on the selected half of the array.

• Repeat until the target element is found or the array is exhausted.

Mongo query to increase age by 20% for documents with age field

• Use $exists operator to filter documents with age field

• Use $mul operator to increase age by 20%

• Example: db.users.updateMany({ age: { $exists: true } }, { $mul: { age: 1.2 } })

The sum of two numbers can be obtained using bitwise operators.

• Use the bitwise XOR operator to get the sum of two numbers without carrying.

• Use the bitwise AND operator to get the carry.

• Repeat the process until there is no carry left.

ID selector is used to select an element with a specific ID attribute in CSS.

• ID selector is denoted by '#' followed by the ID name.

• ID should be unique on a page.

• ID selector has higher specificity than class selector.

• Example: #header { color: blue; }

Search an element in an infinite sorted array using binary search.

• Initialize low as 0 and high as 1.

• Double the high index until arr[high] is greater than the target element.

• Perform binary search between low and high indexes.

Over-indexing in MongoDB can negatively impact performance by increasing memory usage and slowing down query execution.

• Over-indexing can lead to increased memory usage as each index consumes memory.

• Having too many indexes can slow down write operations as each index needs to be updated when a document is inserted, updated, or deleted.

• To prevent over-indexing, carefully analyze query patterns and create indexes only for fields that are frequently queried.

• Regularly review and r...read more

Use the KEYS command in Redis to retrieve all keys containing a specific substring.

• Use the KEYS command followed by the pattern '*xyz*' to retrieve all keys containing the substring 'xyz'.

• Be cautious when using the KEYS command as it can be resource-intensive on large datasets.

• Consider using SCAN command for better performance when dealing with large datasets.

Key factors include data modeling, normalization, indexing, scalability, and performance.

• Consider data modeling to ensure efficient storage and retrieval of data.

• Normalize the database to reduce redundancy and improve data integrity.

• Use indexing to speed up data retrieval operations.

• Design for scalability to accommodate future growth and changes.

• Optimize for performance by considering query optimization and data caching.

Promises are objects representing the eventual completion or failure of an asynchronous operation, while callbacks are functions passed as arguments to be executed after a task is completed.

• Promises allow chaining multiple asynchronous operations, while callbacks can lead to callback hell.

• Promises have built-in error handling through .catch(), while callbacks rely on error-first callbacks.

• Promises are easier to read and maintain due to their sequential nature, while callbacks...read more

I believe no-code tools like XANO are great for rapid prototyping and simplifying development processes.

• No-code tools like XANO allow for faster development by eliminating the need for manual coding

• They are great for prototyping and testing ideas quickly

• XANO specifically offers a visual interface for building backend logic without writing code

• I have used XANO in a few projects and found it to be user-friendly and efficient

ShallowCopy copies only the reference of an object while DeepCopy creates a new object with a new reference.

• ShallowCopy creates a new reference to the same object, so changes made to the copy will reflect in the original object.

• DeepCopy creates a new object with a new reference, so changes made to the copy will not reflect in the original object.

• ShallowCopy is faster and less memory-intensive than DeepCopy.

• DeepCopy is necessary when you need to modify the copied object withou...read more

The request-response cycle in node.js involves a client sending a request to a server, which processes the request and sends back a response.

• Client sends a request to the server using HTTP methods like GET, POST, PUT, DELETE.

• Server receives the request, processes it, and generates a response.

• The response is sent back to the client, typically in the form of HTML, JSON, or other data formats.

• Node.js uses event-driven, non-blocking I/O model to handle multiple requests efficient...read more

Different authentication methods include OAuth, JWT, Basic Auth, and OAuth2.

• OAuth: Allows third-party applications to access resources without sharing credentials.

• JWT (JSON Web Tokens): Securely transmit information between parties as a JSON object.

• Basic Auth: Sends user credentials in the header of each request.

• OAuth2: Authorization framework that enables a third-party application to obtain limited access to an HTTP service.

I would rate my proficiency in data structures and algorithms as an 8.

• I have a strong understanding of common data structures like arrays, linked lists, trees, and graphs.

• I am proficient in implementing algorithms like sorting, searching, and dynamic programming.

• I have experience solving algorithmic problems on platforms like LeetCode and HackerRank.

Find the largest Jumping number less than the given number in Java.

• Create a function to check if a number is a Jumping number.

• Iterate from the given number to 0 and find the largest Jumping number.

• Return the largest Jumping number found.

Steps to connect PostgreSQL to Django

• Install psycopg2 package using pip

• Update DATABASES setting in Django settings.py file

• Specify database name, user, password, host, and port in settings.py

• Run migrations to create necessary database tables

• Test the connection by running Django server

My approach for Heavy Data Handling involves optimizing database queries, using indexing, caching, and implementing efficient algorithms.

• Optimizing database queries by using proper indexing and avoiding unnecessary joins

• Implementing caching mechanisms to reduce the load on the database

• Using efficient algorithms for data processing and manipulation

• Batch processing large datasets to minimize resource usage

• Implementing data partitioning and sharding for scalability

• Utilizing para...read more

Struct is a value type while class is a reference type in C#.

• Structs are stored on the stack while classes are stored on the heap.

• Structs cannot be inherited while classes can be inherited.

• Structs do not support destructors while classes do.

• Structs are used for small data structures while classes are used for larger, more complex objects.

• Example of struct: struct Point { public int X; public int Y; }

• Example of class: class Person { public string Name; public int Age; }

Yes, PHP is a server-side scripting language and MySQL is a relational database management system commonly used together for web development.

• PHP is used to create dynamic web pages and can be embedded in HTML code

• MySQL is used to store and manage data in a relational database

• PHP can connect to MySQL to retrieve and manipulate data

• Examples of websites built with PHP and MySQL include Facebook and WordPress

Popular JavaScript frameworks used for backend development.

• Express.js

• Node.js

• Koa.js

• Hapi.js

• Sails.js

Copy constructor is a special constructor that creates a new object by copying an existing object.

• It is used to create a new object with the same values as an existing object.

• It takes an object of the same class as a parameter.

• It is automatically called when a new object is created from an existing object.

• It creates a deep copy of the object, meaning that all the member variables are copied.

• Example: class MyClass { public: MyClass(const MyClass& obj) { // copy constructor cod...read more

I have been using Python for 5 years and am very comfortable with its syntax and libraries.

• I have 5 years of experience using Python for backend development.

• I am proficient in using Python libraries such as Flask, Django, and SQLAlchemy.

• I have worked on various projects where Python was the primary language for backend development.

• I am comfortable writing clean and efficient code in Python.

Improving merge requests through design enhancements

• Implement a clearer review process with defined roles and responsibilities

• Utilize templates for MRs to ensure consistency and completeness

• Integrate automated testing and code quality checks to streamline the review process

• Provide better documentation and context for changes made in the MR

• Enhance communication channels for feedback and discussions on the MR

Code to implement level order traversal in a tree

• Use a queue data structure to keep track of nodes at each level

• Start by pushing the root node into the queue

• While the queue is not empty, dequeue a node, print its value, and enqueue its children

Singleton is a design pattern that restricts the instantiation of a class to one object.

• Singleton is used when only one instance of a class is required throughout the system.

• It provides a global point of access to the instance.

• Example: Database connection, Logger, Configuration settings.

• Default methods are methods in an interface with a default implementation.

• Volatile keyword is used to indicate that a variable's value will be modified by different threads.

Virtual environments in Django help manage dependencies and isolate project environments.

• Virtual environments prevent conflicts between different projects by isolating dependencies.

• They allow for easy management and installation of project-specific packages.

• Virtual environments ensure that the project runs with the correct versions of dependencies.

• They help in keeping the project clean and organized by separating dependencies from the system-wide packages.

Operator overloading allows operators to have different meanings based on the context of their usage.

• Operator overloading is a feature in object-oriented programming languages.

• It allows operators to be redefined for custom classes.

• For example, the '+' operator can be overloaded to concatenate strings or add numbers.

• It can improve code readability and reduce the amount of code needed for certain operations.

Yes, I have experience in cloud computing.

• I have worked with AWS, Azure, and Google Cloud Platform

• I have experience in deploying and managing applications on cloud servers

• I have knowledge of cloud storage, networking, and security

• I have used tools like Docker and Kubernetes for containerization and orchestration

API features include authentication, rate limiting, versioning, error handling, and documentation.

• Authentication: Ensures only authorized users can access the API.

• Rate limiting: Controls the number of requests a user can make in a given time period.

• Versioning: Allows for different versions of the API to coexist.

• Error handling: Provides meaningful error messages to users.

• Documentation: Describes how to use the API and its endpoints.

Delete removes specific rows from a table, truncate removes all rows, and drop deletes the entire table.

• DELETE: Removes specific rows from a table based on a condition

• TRUNCATE: Removes all rows from a table, but keeps the table structure

• DROP: Deletes the entire table along with its structure

JWT key parameters include header, payload, signature, and expiration time.

• Header: Contains metadata about the token such as the type and hashing algorithm.

• Payload: Contains claims or information about the user.

• Signature: Used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way.

• Expiration Time: Specifies the time after which the JWT expires and should no longer be considered valid.

Event loop is a mechanism in JavaScript that allows asynchronous code to be executed.

• Event loop continuously checks the call stack and the task queue.

• If the call stack is empty, it takes the first task from the queue and pushes it to the call stack.

• Event loop is responsible for handling asynchronous operations in JavaScript.

• setTimeout, setInterval, and AJAX requests are examples of asynchronous operations that use event loop.

The zip() function in Python combines multiple iterables into a single iterable of tuples.

• The zip() function takes in multiple iterables as arguments and returns an iterator of tuples where the i-th tuple contains the i-th element from each of the input iterables.

• If the input iterables are of different lengths, the resulting iterator will only have as many elements as the shortest iterable.

• Example: zip([1, 2, 3], ['a', 'b', 'c']) will return [(1, 'a'), (2, 'b'), (3, 'c')].

ArrayList vs LinkedList: ArrayList uses dynamic array, LinkedList uses linked nodes. Stream APIs for functional programming. Multithreading for concurrent execution.

• ArrayList: faster for random access, slower for insertions/deletions. LinkedList: faster for insertions/deletions, slower for random access.

• Stream APIs: provide functional-style operations on streams of elements. Example: stream.filter(x -> x > 5).forEach(System.out::println);

• Multithreading: allows multiple thread...read more

Asynchronous and synchronous are programming concepts that determine how tasks are executed.

• Synchronous tasks are executed one after the other, in a sequential manner.

• Asynchronous tasks can be executed simultaneously, without waiting for the previous task to complete.

• Synchronous tasks are easier to understand and debug, while asynchronous tasks are more efficient and can improve performance.

• Examples of synchronous tasks include reading a file or waiting for user input, while ...read more

String pool is a storage area in memory where unique string literals are stored to optimize memory usage.

• String pool is a part of the Java heap memory where unique string literals are stored.

• String literals are created using double quotes, and they are stored in the string pool.

• When a new string is created with the same value as an existing string literal, it refers to the same object in the string pool.

• String pool helps in reducing memory usage by reusing existing string lit...read more

Abstract class can have implementation while interface only has method signatures.

• 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 non-public members while interface only has public members.

• Abstract class is used for creating a base class for other classes while interface is used for defining a contract that a class must follow.

• Example of abstract class: p...read more

Double check Singleton Design Pattern ensures only one instance of a class is created.

• Create a private static instance variable in the class.

• Use a private constructor to prevent external instantiation.

• Implement a static method to return the instance, checking for null and creating a new instance if needed.

var is function scoped, let and const are block scoped.

• var can be redeclared and updated within its scope

• let can be updated but not redeclared within its scope

• const cannot be updated or redeclared once declared

• let and const are not hoisted like var

• const must be initialized during declaration

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope.

• Hoisting applies to variable and function declarations, not initializations

• Variables declared with let and const are not hoisted

• Function declarations are hoisted before variable declarations

• Function expressions are not hoisted

Commands for creating a new Django project

• Use 'django-admin startproject project_name' to create a new Django project

• Navigate to the project directory using 'cd project_name'

• Run 'python manage.py startapp app_name' to create a new app within the project

JWT token is a JSON Web Token used for securely transmitting information between parties.

• JWT token is an encoded string that contains information about the user and is digitally signed to ensure its authenticity.

• It consists of three parts separated by dots: header, payload, and signature.

• JWT tokens are commonly used for authentication and authorization in web applications.

• Example: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0Ijo...read more

A data pipeline is a series of steps that move data from one system to another, transforming it along the way.

• Identify data sources and destinations

• Choose appropriate tools for extraction, transformation, and loading (ETL)

• Design the pipeline architecture

• Test and monitor the pipeline for errors

• Optimize the pipeline for performance and scalability

Code to find prime numbers in Java

• Use a loop to iterate through numbers and check if each number is prime

• A prime number is a number that is only divisible by 1 and itself

• Start checking from 2 up to the number itself, if any number divides it then it is not prime