Backend Developer Interview Questions

Backend development involves working on the server side of web applications, where the logic, database interactions, and server management take place. It focuses on handling data, processing requests from clients, and generating appropriate responses.

In this Top Backend Development interview questions, we cover backend development interview questions from basic to advanced topics such as JavaScript, NodeJS, ExpressJS, SQL, MongoDB, Django, PHP, Java Spring, and APIs. Whether you are a fresher or an experienced professional, these questions will enhance your skills and help you excel in backend development interviews.

Backend Developer Interview Questions

Here, we have organized 85+ backend developer interview questions and answers based on different technologies, including

JavaScript Interview Questions

Before going to learn Node or ExpressJS it's better to learn the important JavaScript concepts that will be used in the backend.

1. Explain equality in JavaScript

In JavaScript, the equality operator is used for equality comparison. It compares two values and returns true if they are equal, and false otherwise. However, it performs type coercion, which means it converts the operands to the same type before making the comparison.

console.log(5 == '5'); // true, because '5' is converted to a number before comparison
console.log(5 == 5);    // true, both values are of the same type and equal
console.log(5 == 6);    // false, the values are not equal

true
true
false

2. Explain Function.prototype.bind.

In JavaScript, Function.prototype.bind() is a method that allows We can create a new function with a specified this value and optionally some initial arguments.

Syntax:

const newFunction = oldFunction.bind(thisArg, arg1, ag2, ..., argN)

3. Explain the difference between Objects. freeze() vs const

Here is the difference of objects.freeze() vs const

Object.freeze()

• Object.freeze() is a method provided by JavaScript that freezes an object, making it immutable. This means that after calling Object.freeze() on an object, We cannot add, delete, or modify any of its properties.
• Even attempts to modify the properties of a frozen object will fail silently in non-strict mode and throw an error in strict mode.
• Object.freeze() operates on the object itself, making the object and its properties immutable.

Const

• const is a keyword in JavaScript used to declare constants. When We declare a variable using const, We cannot reassign it to a different value. However, this does not make the object itself immutable.
• If the variable is an object, its properties can still be modified or reassigned, but We cannot assign a new object to the variable.
• In other words, const ensures that the variable reference cannot change, but it does not ensure immutability of the object itself.

4. What are IIFEs (Immediately Invoked Function Expressions)?

IIFEs stands for Immediately Invoked Function Expressions. JavaScript functions that are executed immediately after they are defined. They are commonly used to create a new scope and encapsulate code, preventing variable declarations from polluting the global scope.

Syntax:

(function (){ 
// Function Logic Here. 
})();

5. Can We describe the main difference between a .forEach loop and a .map() loop and why We would pick one versus the other?

Here is the difference between forEach loop and map() loop

.forEach():

• The .forEach() method is used to iterate over an array and execute a provided function once for each array element.
• It does not mutate the original array and does not return a new array.
• The callback function passed to .forEach() can perform actions on each element of the array, but it does not produce a new array.

.map():

• The .map() method is used to iterate over an array and transform each element using a provided function.
• It returns a new array with the results of calling the provided function on each element of the original array.
• The callback function passed to .map() should return a new value for each element, which will be included in the new array.

6. What is a cookie? How can We create, read and clear cookies using Javascript?

A cookie is an important tool as it allows We to store the user information as a name-value pair separated by a semi-colon in a string format. If we save a cookie in our browser then we can log in directly to the browser because it saves the user information.

• Create cookies: We can apply various operations on cookie-like create, delete, read, add an expiry date to it so that users can never be logged in after a specific time. A cookie is created by the document.cookie keyword.
• Read cookies: This function retrieves the cookie data stored in the browser. The cookie string is automatically encoded while sending it from the server to the browser.
• Clear cookies: Cookies expire, the date and time are specified in the “expires” attribute. As a result, the browser automatically deletes the cookies when the date and time exceed the expiration date (and time).

7. What are Closures in JavaScript?

JavaScript closure is a feature that allows inner functions to access the outer scope of a function. Closure helps in binding a function to its outer boundary and is created automatically whenever a function is created.

function foo(outer_arg) {

    function inner(inner_arg) {
        return outer_arg + inner_arg;
    }
    return inner;
}
let get_func_inner = foo(5);

console.log(get_func_inner(4));
console.log(get_func_inner(3));

9
8

The foo function returns an inner function that adds its argument to the outer function's argument. It creates a closure, preserving the outer function's state.

8. What are the arrow functions in JavaScript?

Arrow function {()=>} is concise way of writing JavaScript functions in shorter way. Arrow functions were introduced in the ES6 version. They make our code more structured and readable. Mostly in development phase mostly arrow function is used.

Syntax

const gfg = () => {
    console.log( "Hi Geek!" );
}
gfg() // output will be Hi Geek!

9. What are Imports and Exports in JavaScript?

Exports:

• Exports are used to expose functionality from a module to other parts of the program.
• We can export variables, functions, classes, or any other JavaScript entity by using the export keyword.
• There are different ways to export:
  • Default Export: export default myFunction;
  • Named Export: export const myVariable = 10;
  • Named Exports from Expressions: export { myFunction };
• We can have multiple exports in a single module.

Imports:

• Imports are used to bring functionality from other modules into the current module.
• We can import exported entities using the import keyword.
• We can import default exports like this: import myFunction from './module';
• We can import named exports like this: import { myVariable } from './module';
• We can also import all named exports using the * as syntax: import * as module from './module';

10. What are the various Operators in Javascript?

JavaScript operators operate the operands, these are symbols that are used to manipulate a certain value or operand. Operators are used to performing specific mathematical and logical computations on operands.

NodeJS Backend Developer Interview Questions

11. What is NodeJS and how it works?

NodeJS is a JavaScript runtime environment that allows developers to run JavaScript code outside of a web browser. It uses the V8 JavaScript engine, which is the same engine used by Google Chrome, to execute JavaScript code on the server-side.

• NodeJS works on an event-driven, non-blocking I/O model, enabling efficient and scalable server-side applications.
• It uses asynchronous programming to handle multiple requests simultaneously, making it ideal for real-time web apps, APIs, and microservices.
• With a vast library ecosystem, NodeJS extends its capabilities for various use cases.

12. How do we manage packages in a NodeJS project?

Modules are the blocks of reusable code consisting of Javascript functions and objects which communicate with external applications based on functionality. A package is often confused with modules, but it is simply a collection of modules (libraries).

13. How can we use async await in NodeJS?

To use async await in NodeJS:

• Define an asynchronous function with the async keyword.
• Use the await keyword within the function to pause execution until promises are resolved.
• Handle errors using try/catch blocks.
• Call the asynchronous function and use await to wait for its result.

Example: After async/await

async function fun1(req, res){
  let response = await request.get('http://localhost:3000');
    if (response.err) { console.log('error');}
    else { console.log('fetched response');
}

14. What is NodeJS streams?

Streams are one of the fundamental concepts of NodeJS. Streams are a type of data-handling methods and are used to read or write input into output sequentially. Streams are used to handle reading/writing files or exchanging information in an efficient way.

Accessing Streams:

const fs = require("fs");

const readStream = fs.createReadStream("source.txt");
const writeStream = fs.createWriteStream("destination.txt");

readStream.pipe(writeStream)
  .on("error", console.log);

writeStream.on("finish", () => 
  console.log("Data successfully copied!")
);

15. Describe the exit codes of NodeJS?

NodeJS is a cross-platform, open-source back-end JavaScript runtime environment that uses the V8 engine to execute JavaScript code outside of a web browser. Exit codes in NodeJS are a specific group of codes that finish off processes, which can include global objects as well.

16. Explain the concept of stub in NodeJS?

A small program routine that substitutes for a longer program which is possible to be loaded later or that is remotely located.

Features of stub

• Stubs can be either anonymous.
• Stubs can be wrapped into existing functions. When we wrap a stub into the existing function the original function is not called.

17. How can we enhance the performance of NodeJS?

Clustering is the process through which we can use multiple cores of our central processing unit at the same time with the help of NodeJS, which helps to increase the performance of the software and also reduces its time load.

We can install cluster modules through the given command.

npm i cluster

18. What is WASI and why is it being introduced?

WASI provides a standard way to talk to the outside world like operating system so that so that it can ask to read the file or perform the other operations .

• WASI (WebAssembly System Interface) acts as a bridge between WebAssembly and the operating system.
• WebAssembly translates languages like C++ or Rust into a format browsers understand.
• Browsers only understand JavaScript, so WebAssembly enables execution of other languages.
• WASI provides a standard way for WebAssembly to interact with the OS.
• It allows WebAssembly to perform system operations like file reading and writing.

19. How to measure the duration of async operations?

Asynchronous operation in NodeJS is a non-blocking operation which means if we perform an asynchronous operation at a certain point in code then the code after that is executed and does not wait for this asynchronous operation to complete.

Syntax

const calcTime = async () => {
    const start = Date.now();
    await someAsyncOperation();
    const end = Date.now()
    const duration = end - start;
}

20. What is a thread pool and which library handles it in NodeJS?

A thread pool is a collection of worker threads that are used to execute asynchronous tasks concurrently in a multithreaded environment.

In NodeJS, the libuv library handles the thread pool.

• Thread pool is a collection of worker threads for concurrent task execution.
• Prevents new thread creation for each task, improving efficiency.
• NodeJS uses libuv to manage the thread pool.
• Libuv handles async I/O, including file system, network, and timers.

ExpressJs Backend Developer Interview Questions

21. How does ExpressJS handle middleware?

ExpressJS is a routing and Middleware framework for handling the different routing of the webpage and it works between the request and response cycle. Middleware gets executed after the server receives the request and before the controller actions send the response.

The basic syntax for the middleware functions are as follows

app.get(path, (req, res, next) => {}, (req, res) => {})

22. How does ExpressJS handle request and response objects?

In ExpressJS, request and response objects are fundamental to handling HTTP requests and generating HTTP responses. Here's how ExpressJS handles these objects:

1. Request Object (req): Represents the client's HTTP request, containing method, URL, headers, query params, and body. Express passes it to route handlers and middleware.
2. Response Object (res): Represents the server's response, allowing data sending, status control, and header setting. Supports methods like res.json(), res.send(), res.redirect(), and res.setHeader().

23. How can we create a Rest API route in ExpressJS?

NodeJS server code sets up a RESTful API for managing data. It provides endpoints for performing CRUD (Create, Read, Update, Delete) operations on a collection of records. The server uses the ExpressJS framework to handle HTTP requests.

24. What is the difference between a traditional server and an ExpressJS server?

25. What is Token-based Authentication? What is JWT?

Token-Based Authentication is a security mechanism where a user logs in and receives a token, which is then used for subsequent requests instead of credentials. This approach enhances security and scalability, especially in stateless applications like REST APIs.

A JSON web token(JWT) is a compact, self-contained token format used for securely transmitting information between parties. It consists of three parts:

• Header: Contains metadata, such as the token type and signing algorithm.
• Payload: Holds the claims (user data or permissions).
• Signature: Ensures integrity and authenticity by verifying the token with a secret key.

26. What is Pub-Sub architecture?

Publisher Subscriber basically known as Pub-Sub is an asynchronous message-passing system that solves the drawback above. The sender is called the publisher whereas the receiver is called the subscriber. The main advantage of pub-sub is that it decouples the subsystem which means all the components can work independently.

27. Write a code to get post a query in ExpressJS.

POST parameter can be received from a form using express.urlencoded() middleware and the req.body Object. The express.urlencoded() middleware helps to parse the data that is coming from the client-side.

const express = require('express');
const app = express();

app.use(express.urlencoded({ extended: true }));

app.post('/submit', (req, res) => {
    const { name, email } = req.body;

    console.log('Received form submission:');
    console.log('Name:', name);
    console.log('Email:', email);
    
    res.send('Form submitted successfully');
});
const port = process.env.PORT || 3000;
app.listen(port, () => {
    console.log(`Server is running on port ${port}`);
});

In this code

• app.use(express.urlencoded({ extended: true })) enables parsing of application/x-www-form-urlencoded request bodies.
• A POST route /submit handles form submissions.
• req.body extracts name and email via middleware.
• Data is processed (logged to console).
• Response sent using res.send().

28. What do We understand by Scaffolding in ExpressJS?

Scaffolding is creating the skeleton structure of application. It allows users to create own public directories, routes, views etc. Once the structure for app is built, user can start building it.

Syntax

npm install express --save

29. Explain Error Handling in ExpressJS

Error handling in ExpressJS refers to the process of capturing and responding to errors that occur during the execution of an Express application.

In Express, We can handle errors using middleware functions, which are functions that have access to the request and response objects, as well as the next middleware function in the application’s request-response cycle.

30. How to do Templating using ExpressJS in NodeJS?

A template engine basically helps us to use the static template files with minimal code. At runtime, the template engine replaces all the variables with actual values at the client-side.

To use templating with ExpressJS in NodeJS:

1. Install a template engine like EJS (npm install ejs).
2. Set up Express to use the template engine (app.set('view engine', 'ejs')).
3. Create EJS templates in the views directory.
4. Render EJS templates in Express routes using res.render().
5. Pass dynamic data to the templates.
6. Start the Express server.

SQL Backend Developer Interview Questions

31. What is the difference between LEFT JOIN with WHERE clause & LEFT JOIN?

LEFT JOIN with WHERE Clause:

SELECT *
FROM table1
LEFT JOIN table2 ON table1.column = table2.column
WHERE table2.column IS NULL;

• This query performs a LEFT JOIN between table1 and table2 based on the specified column.
• The WHERE clause filters the results to only include rows where there is no match in table2 (i.e., table2.column IS NULL).
• It effectively retrieves records from table1 and the matching records from table2, where no match is found, the columns from table2 will be NUL.

Regular LEFT JOIN:

SELECT *  
FROM table1  
LEFT JOIN table2 ON table1.column = table2.column  
WHERE table2.column IS NULL;

• Retrieves records from table1 where no match is found in table2.
• The WHERE table2.column IS NULL filters out matching rows.
• Used to find unmatched records from table1.

32. How do We prevent SQL Server from giving We informational messages during and after a SQL statement execution?

In SQL Server, informational messages, often called "info" or "print" messages, can be generated during and after the execution of a SQL statement. These messages might include details such as the number of rows affected or certain warnings. If We want to suppress these informational messages, We can use the SET command with the NOCOUNT option.

SET NOCOUNT ON;
-- Wer SQL statements go here
SET NOCOUNT OFF;

• SET NOCOUNT ON;: This setting turns off the "row affected" informational messages for subsequent statements in the same batch.
• SET NOCOUNT OFF;: This setting turns the informational messages back on.

33. What is Cursor? How to use a Cursor?

Cursor is a Temporary Memory or Temporary Work Station. It is Allocated by Database Server at the Time of Performing DML(Data Manipulation Language) operations on the Table by the User. Cursors are used to store Database Tables. 

There are two types of Cursors:

1. Implicit Cursors: Implicit Cursors are also known as Default Cursors of SQL SERVER. These Cursors are allocated by SQL SERVER when the user performs DML operations.
2. Explicit Cursors: Explicit Cursors are Created by Users whenever the user requires them. Explicit Cursors are used for Fetching data from Table in Row-By-Row Manner.

34. How SQL Server executes a statement with nested subqueries?

When SQL Server processes a statement with nested subqueries execution process involves evaluating each subquery from the innermost to the outermost level. The general steps for executing a statement with nested subqueries are as follows:

• Parsing & Compilation: SQL Server parses the query and creates an execution plan.
• Innermost Subquery Execution: The innermost subquery runs first, producing a value or set of values.
• Intermediate Storage: If needed, results are stored in temporary structures.
• Propagation: These results are passed to the next query level.
• Higher-Level Execution: This process continues for higher-level subqueries and the main query.
• Result Combination: Data from all levels is combined to produce the final output.
• Query Optimization: SQL Server optimizes execution by reordering joins and selecting efficient indexes.

35. What is a deadlock and what is a live lock?

Deadlock: Occurs when two or more transactions wait indefinitely for each other to release a resource, causing a standstill.

How to Fix Deadlocks:

1. Prevention:

• Allocate resources carefully to avoid conflicts.
• Follow a fixed order when requesting resources.

2. Detection & Resolution:

• Use timeouts or deadlock detection mechanisms.
• Rollback one transaction (victim) to allow others to proceed.

3. Transaction Timeout:

• Set a time limit for transactions; rollback if it exceeds the limit.

4. Lock Hierarchy:

• Always acquire locks in a structured order to prevent circular waits.

5. Avoidance Algorithms:

• Predict and prevent deadlocks before allocating resources.

37. Where is the MyISAM table stored?

Stored as Files: Each MyISAM table has three files:

• .frm – Table structure.
• .MYD – Table data.
• .MYI – Indexes.

Location:

• Linux: /var/lib/mysql/
• Windows: C:\ProgramData\MySQL\MySQL Server X.Y\data\

Locking: Uses table-level locking, which can cause contention.

Optimization: OPTIMIZE TABLE improves performance.

Consideration: InnoDB is preferred for transactions and better concurrency.

MongoDB Backend Developer Interview Questions

38. What is BSON in MongoDB?

BSON stands for Binary JSON. It is a binary file format that is used to store serialized JSON documents in a binary-encoded format.

The MongoDB database had several scalar data formats that were of special interest only for MongoDB, hence they developed the BSON data format to be used while transferring files over the network.

39. What are Replication and Sharding in MongoDB?

Replication - is the method of duplication of data across multiple servers. For example, we have an application and it reads and writes data to a database and says this server A has a name and balance which will be copied/replicate to two other servers in two different locations.

Sharding - is a method for allocating data across multiple machines. MongoDB used sharding to help deployment with very big data sets and large throughput the operation. By sharding, We combine more devices to carry data extension and the needs of read and write operations.

40. When should we embed one document within another in MongoDB?

MongoDB provides We read operations to retrieve embedded/nested documents from the collection or query a collection for a embedded/nested document. We can perform read operations using the db.collection.find() method.

41. Can We create an index on an array field in MongoDB? If yes, what happens in this case?

Yes, We can create an index on a field containing an array value to improve performance for queries on that field. When We create an index on a field containing an array value, MongoDB stores that index as a multikey index.

To create an index, use the db.collection.createIndex() method.

db.<collection>.createIndex( { <field>: <sortOrder> } )

The example uses a students collection that contains these documents:

db.students.insertMany([
    {
        "name": "Andre Robinson",
        "test_scores": [88, 97]
    },
    {
        "name": "Wei Zhang",
        "test_scores": [62, 73]
    },
    {
        "name": "Jacob Meyer",
        "test_scores": [92, 89]
    }
])

Procedure: The following operation creates an ascending multikey index on the test_scores field of the students collection:

db.students.createIndex( { test_scores: 1 } )

42. What is Shard Key in MongoDB and how does it affect development process?

Shard key, which is a unique identifier that is used to map the data to its corresponding shard. When a query is received, the system uses the shard key to determine which shard contains the required data and then sends the query to the appropriate server or node.

43. What is ObjectId in MongoDB?

Every document in the collection has an “_id” field that is used to uniquely identify the document in a particular collection it acts as the primary key for the documents in the collection. “_id” field can be used in any format and the default format is ObjectId of the document.

ObjectId(<hexadecimal>)

44. What is a Covered Query in MongoDB?

A covered query in MongoDB is a type of query where all the fields needed for the query are covered by an index. For a query to be considered covered the following conditions must be met:

• Projection: The query must include a projection that only selects fields covered by the index. A projection specifies which fields to include or exclude in the query results.
• Index: The fields specified in the query's filter criteria must be part of an index. The fields specified in the projection must be part of the same index.
• No Additional Document Fields: The query should not include additional fields or expressions that are not covered by the index. If additional fields are needed, the index might not cover the entire query.

 { "_id": 1, "name": "Alice", "age": 30, "department": "HR" }
 { "_id": 2, "name": "Bob", "age": 35, "department": "IT" }
 { "_id": 3, "name": "Charlie", "age": 28, "department": "HR" }

Let's say We have an index on the "department" field:

 db.employees.createIndex({ "department": 1 });

Now, if We perform a query like this:

db.employees.find({ "department": "HR" }, { "_id": 0, "name": 1 });

In this query:

• The filter criteria ({ "department": "HR" }) matches the indexed field.
• The projection ({ "_id": 0, "name": 1 }) includes only the "name" field, which is also part of the index.

45. How to Create Relationship in MongoDB?

In MongoDB, a relationship represents how different types of documents are logically related to each other. Relationships like one-to-one, one-to-many, etc., can be represented by using two different models:

1. Embedded document model
2. Reference model

46. What is CAP theorem?

The CAP theorem, originally introduced as the CAP principle, can be used to explain some of the competing requirements in a distributed system with replication. It is a tool used to make system designers aware of the trade-offs while designing networked shared-data systems. 

47. What is Indexing in MongoDB?

MongoDB uses indexing in order to make the query processing more efficient. If there is no indexing, then the MongoDB must scan every document in the collection and retrieve only those documents that match the query. Indexes are special data structures that stores some information related to the documents such that it becomes easy for MongoDB to find the right data file.

Django Backend Developer Interview Questions

48. Explain Django Architecture?

Django is a Python-based web framework which allows We to quickly create web application without all of the installation or dependency problems that We normally will find with other frameworks. Django is based on MVT (Model-View-Template) architecture. MVT is a software design pattern for developing a web application.

49.What are templates in Django or Django template language?

Templates are the third and most important part of Django’s MVT Structure. A template in Django is basically written in HTML, CSS, and Javascript in a .html file. Django framework efficiently handles and generates dynamic HTML web pages that are visible to the end-user. 

50. What is Django ORM?

Django lets us interact with its database models, i.e. add, delete, modify, and query objects, using a database-abstraction API called ORM(Object Relational Mapper). Django’s Object-Relational Mapping (ORM) system, a fundamental component that bridges the gap between the database and the application’s code.

51. How to get a particular item in the Model?

In Django, We can retrieve a particular item (a specific record or instance) from a model using the model's manager and a query.
Assuming We have a Django model named WerModel defined in an app named Wer_app:

• Import the Model: Make sure to import Wer model in the Python file where We need to retrieve the item.

from Wer_app.models import WerModel

• Use the Model's Manager: Every Django model comes with a default manager called objects. We can use this manager to perform queries on the model.
• Perform the Query: Use a query to filter the items based on the criteria We want. For example, if We want to retrieve an item by its primary key (id field), We can use the get method.

52. Difference between select related and prefetch related?

In Django, select_related and prefetch_related are designed to stop the deluge of database queries that are caused by accessing related objects.

• select_related() “follows” foreign-key relationships, selecting additional related-object data when it executes its query.
• prefetch_related() does a separate lookup for each relationship and does the “joining” in Python.

53. How can We combine multiple QuerySets in a View?

A QuerySet is a collection of database queries to retrieve data from Wer database. It represents a set of records from a database table or a result of a database query. Query sets are lazy, meaning they are not evaluated until We explicitly request the data, which makes them highly efficient.

54. What is Django Field Choices?

Django Field Choices. According to documentation Field Choices are a sequence consisting itself of iterables of exactly two items (e.g. [(A, B), (A, B) …]) to use as choices for some field.Choices limits the input from the user to the particular values specified in models.py. If choices are given, they’re enforced by model validation and the default form widget will be a select box with these choices instead of the standard text field.

55. What are Django URLs?

In Django, views are Python functions which take a URL request as parameter and return an HTTP response or throw an exception like 404. Each view needs to be mapped to a corresponding URL pattern. This is done via a Python module called URLConf (URL configuration).

from django.contrib import admin 
from django.urls import path, include 

urlpatterns = [ 
    path('admin/', admin.site.urls), 
    path('', include('books.urls')), 
] 

56. What are the views of Django?

Django Views are one of the vital participants of MVT Structure of Django. As per Django Documentation, A view function is a Python function that takes a Web request and returns a Web response. This response can be the HTML contents of a Web page, or a redirect, or a 404 error, or an XML document, or an image, anything that a web browser can display. 

57. What are the models in Django?

A Django model is the built-in feature that Django uses to create tables, their fields, and various constraints. In short, Django Models is the SQL Database one uses with Django. SQL (Structured Query Language) is complex and involves a lot of different queries for creating, deleting, updating, or any other stuff related to a database.

from django.db import models

# Create your models here.
class GeeksModel(models.Model):
    title = models.CharField(max_length = 200)
    description = models.TextField()

PHP Backend Developer Interview Questions

58. How do We enable error reporting in PHP?

The error_reporting() function sets the error_reporting directive at runtime. PHP has many levels of errors, using this function sets that level for the duration (runtime) of Wer script. If the optional error_level is not set, error_reporting() will just return the current error reporting level.

59. How is the explode() function used?

The explode() function is an inbuilt function in PHP used to split a string into different strings. The explode() function splits a string based on a string delimiter, i.e. it splits the string wherever the delimiter character occurs. This function returns an array containing the strings formed by splitting the original string.

Syntax:

array explode(separator, OriginalString, NoOfElements)

60. How does the array walk function work in PHP?

The array_walk() function is an inbuilt function in PHP. The array_walk() function walks through the entire array regardless of pointer position and applies a callback function or user-defined function to every element of the array. The array element’s keys and values are parameters in the callback function.

Syntax:

boolean array_walk($array, myFunction, $extraParam)

61. How are the $_get and $_post variables used in PHP?

A web browser may be the client, and an application on a computer that hosts a website may be the server. A client (browser) submits an HTTP request to the server; then the server returns a response to the client. The response contains status information about the request and may also contain the requested content.

• GET: Requests data from a specified resource.
• POST: Submits data to be processed to a specified resource.

62. When would We use === instead of ==?

• Operator: This operator is used to check the given values are equal or not. If yes, it returns true, otherwise it returns false.

operand1 == operand2

• === Operator: This operator is used to check the given values and its data type are equal or not. If yes, then it returns true, otherwise it returns false.

operand1 === operand2

63. What is MVC and what does each component do?

The Model-View-Controller (MVC) framework is an architectural/design pattern that separates an application into three main logical components Model, View, and Controller. Each architectural component is built to handle specific development aspects of an application. It isolates the business logic and presentation layer from each other.

64. What are the differences between die() and exit() functions in PHP?

PHP exit() Function: In PHP, the exit() function prints a message and exits the application. It’s often used to print a different message in the event of a mistake. Use exit() when there is not an error and have to stop the execution.

exit("Message goes here");
or
exit();

PHP die() Function: In PHP, die() is the same as exit(). A program’s result will be an empty screen. Use die() when there is an error and have to stop the execution.

die("Message goes here"); 
or 
die();

65. What is stdClass in PHP?

The stdClass is the empty class in PHP which is used to cast other types to object. It is similar to Java or Python object. The stdClass is not the base class of the objects. If an object is converted to object, it is not modified. But, if object type is converted/type-casted an instance of stdClass is created, if it is not NULL. If it is NULL, the new instance will be empty.

66. How would We create a Singleton class using PHP?

When We don’t want to have more than a single instance of a given class, then the Singleton Design Pattern is used and hence the name is Singleton.

• Singleton is the design patterns in PHP OOPs concept that is a special kind of class that can be instantiated only once.
• If the object of that class is already instantiated then, instead of creating a new one, it gets returned.

67. What is Spring Boot Application?

Spring Boot is built on the top of the spring and contains all the features of spring. And is becoming a favorite of developers these days because of its rapid production-ready environment which enables the developers to directly focus on the logic instead of struggling with the configuration and setup.

Java Spring Backend Developer Interview Questions

68. What Are the Benefits of Using Spring?

Here is the benefits of using spring:

1. Modularity: Lightweight and modular design.
2. Inversion of Control (IoC): Manages object lifecycle and reduces coupling.
3. Aspect-Oriented Programming (AOP): Modularizes cross-cutting concerns.
4. Dependency Injection (DI): Promotes loose coupling and testability.
5. Transaction Management: Simplifies database transactions.
6. Integration: Seamlessly integrates with existing technologies.
7. Enterprise Features: Provides support for security, caching, messaging, etc.
8. Testability and Maintainability: Promotes unit testing and modular design.

69. What is Spring Boot Multi-Module Project.

A Spring Boot Multi-Module Project is a project structure where We organize Wer codebase into multiple modules, each representing a different functional or logical unit of Wer application. Spring Boot, a popular Java framework, provides support for creating and managing multi-module projects.

In a multi-module project, We typically have a parent module (also known as the aggregator module) and one or more child modules. The parent module coordinates the build process and manages the dependencies between the child modules.

70. What Is Dependency Injection?

Dependency Injection is the main functionality provided by Spring IOC(Inversion of Control). The Spring-Core module is responsible for injecting dependencies through either Constructor or Setter methods. The design principle of Inversion of Control emphasizes keeping the Java classes independent of each other and the container frees them from object creation and maintenance.

71. What Is the Difference Between BeanFactory and ApplicationContext?

Here is the differnce between BeanFactory and ApplicationContext

The BeanFactory Interface

This is the root interface for accessing a Spring bean container. It is the actual container that instantiates, configures, and manages a number of beans. These beans collaborate with one another and thus have dependencies between themselves.

ClassPathResource resource = new ClassPathResource("beans.xml");
XmlBeanFactory factory = new XmlBeanFactory(resource);

The ApplicationContext Interface

This interface is designed on top of the BeanFactory interface. The ApplicationContext interface is the advanced container that enhances BeanFactory functionality in a more framework-oriented style.

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

72. Describe the Spring bean lifecycle.

Bean life cycle is managed by the spring container. When we run the program then, first of all, the spring container gets started. After that, the container creates the instance of a bean as per the request, and then dependencies are injected. And finally, the bean is destroyed when the spring container is closed.

73. How to Set Context Path in Spring Boot Application?

The context path is a prefix to the URL path used to identify and differentiate between different context(s). In Spring Boot, by default, the applications are accessed by context path “/”. That means we can access the application directly at http://localhost:PORT/. For example

http://localhost:8080/

74. Explain the difference between @Before, @After, and @Around advice in AOP.

Here is the difference between @Before, @After, and @Around

• @Around: This is the most effective advice among all other advice. The first parameter is of type ProceedingJoinPoint. Code should contain proceed() on the ProceedingJoinPoint and it causes the underlying lines of code to execute.
• @Before: This advice will run as a first step if there is no @Around advice. If @Around is there, it will run after the beginning portion of @Around.
• @After: This advice will run as a step after @Before advice if there is no @Around advice. If @Around is there, it will run after the ending portion of @Around.
• @AfterReturning: This advice will run as a step after @After advice. Usually, this is the place , where we need to inform about the successful resultant of the method.

75. What is autowiring in spring?

The Spring container detects those dependencies specified in the configuration file and @ the relationship between the beans.

• This is referred to as autowiring in Spring.
• An autowired application requires fewer lines of code comparatively but at the same time, it provides very little flexibility to the programmer.

76. What Is Spring Security?

Spring Security is a framework that allows a programmer to use JEE components to set security limitations on Spring-framework-based Web applications. In a nutshell it’s a library that can be utilized and customized to suit the demands of the programmer. 

77. What is Spring IOC Container?

Spring IoC Container is the core of Spring Framework. It creates the objects, configures and assembles their dependencies, manages their entire life cycle. The Container uses Dependency Injection(DI) to manage the components that make up the application.

API Backend Developer Interview Questions

78. What is an API (Application Programming Interface)?

API is an abbreviation for Application Programming Interface which is a collection of communication protocols and subroutines used by various programs to communicate between them. A programmer can make use of various API tools to make their program easier and simpler.

79. What is REST?

Representational State Transfer (REST) is an architectural style that defines a set of constraints to be used for creating web services. 

• REST API is a way of accessing web services in a simple and flexible way without having any processing.
• REST technology is generally preferred to the more robust Simple Object Access Protocol (SOAP) technology.

80. What is a URI?

URI stands for Uniform Resource Identifier. It is a technical term that used for the names of all resources Connected to the World Wide Web. URIs established the protocols over the internet to conduct the connection between among resources.

81. What is RESTful?

RESTful web services are generally highly scalable, light, and maintainable and are used to create APIs for web-based applications. It exposes API from an application in a secure and stateless manner to the client. The protocol for REST is HTTP.

82. What are the REST API Architectural Constraints?

REST is a software architectural style that defines the set of rules to be used for creating web services. Web services which follow the REST architectural style are known as RESTful web services. There are six architectural constraints which makes any web service are listed below:

• Uniform Interface
• Stateless
• Cacheable
• Client-Server
• Layered System
• Code on Demand

83. What is the difference between the POST method and the PUT method?

Here is the difference between the Post and Put method :

HTTP PUT Request

HTTP PUT is a request method supported by HTTP used by the World Wide Web. The PUT method requests that the enclosed entity be stored under the supplied URI.

import requests
# Making a PUT request
r = requests.put('https://httpbin.org/put', data={'key':'value'})

#check status code for response received
# success code - 200
print(r)

# print content of request
print(r.content)

HTTP POST Request

HTTP POST is a request method supported by HTTP used by the World Wide Web. By design, the POST request method requests that a web server accepts the data enclosed in the body of the request message, most likely for storing it.

import requests
# Making a POST request
r = requests.post('https://httpbin.org/post', data={'key':'value'})

#check status code for response received
# success code - 200
print(r)

# print content of request
print(r.json())

84. What are HTTP Status Codes?

HTTP status codes are a set of standardized three-digit numbers used by web servers to communicate the outcome of an HTTP request made by a client. They provide information about whether the request was successful, encountered an error, or requires further action by the client.

• 1xx - Informational: Request received, continuing process.
• 2xx - Success: The action was successfully received, understood, and accepted.
• 3xx - Redirection: Further action needs to be taken in order to complete the request.
• 4xx - Client Error: The request contains bad syntax or cannot be fulfilled.
• 5xx - Server Error: The server failed to fulfill an apparently valid request.

85. How do We keep REST APIs secure?

There are three types of security mechanism for an API – 

• HTTP Basic Authentication: In this mechanism HTTP User Agent provides a Username and Password. Since this method depends only on HTTP Header and entire authentication data is transmitted on insecure lines
• API Keys: API Keys came into picture due to slow speed and highly vulnerable nature of HTTP Basic Authentication.
• OAuth: OAuth is not only a method of Authentication or Authorization, but it’s also a mixture of both the methods. Whenever an API is called using OAuth credential, user logs into the system, generating a token.

86. What are cache-control headers?

The Cache-Control header is a general header, that specifies the caching policies of server responses as well as client requests. Basically, it gives information about the manner in which a particular resource is cached, location of the cached resource, and its maximum age attained before getting expired i.e. time to live.

Syntax:

Cache-Control: <directive> [, <directive>]*

87. What is API Integration?

The process of connecting two or more software applications or processes using APIs is referred to as API integration. This allows the systems to exchange data and functionality, allowing them to work in unison. APIs are a collection of protocols, routines, and tools used to create software and applications.

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• Interview Preparation
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