Capgemini Full Stack Interview Questions and Answers

1. What is @Directive in Angular?

@Directive: This Angular decorator is used to create directives, which are classes that can add behavior to elements in your Angular applications. Directives can be structural (like *ngIf) or attribute-based (like ngModel).

import { Directive, ElementRef, Renderer2 } from @angular/core @Directive({ selector: [appHighlight] }) export class HighlightDirective { constructor(el: ElementRef, renderer: Renderer2) { renderer.setStyle(el.nativeElement, backgroundColor yellow); } }

2. What is the difference between var, let, and const in JavaScript?

var: Declares a variable that is function-scoped or globally-scoped if not inside a function. Variables declared with var are hoisted to the top of their scope and can be re-declared and updated.

let: Declares a block-scoped variable. Variables declared with let are not hoisted in the same way as var and cannot be re-declared.

const: Declares a block-scoped, read-only variable. Variables declared with const cannot be re-declared or updated.

3. What are functional components and class components in React?

Functional components are JavaScript functions that return React elements. They are simpler and primarily used for presenting UI. Since React 16.8, functional components can also manage state and lifecycle methods using hooks.

Class components are ES6 classes that extend from React.Component. They can have state and lifecycle methods. It makes them more powerful and complex than functional components.

4. What are higher-order functions?

Higher-order functions are functions that operate on other functions, either by taking them as arguments or returning them.

5. What is the Java Memory Model (JMM)?

The Java Memory Model (JMM) defines how threads interact through memory and what behaviors are allowed in concurrent execution. It governs visibility and ordering of variable accesses (reads/writes) across threads.

Visibility: Changes made by one thread to shared variables are visible to other threads.
Ordering: The JMM allows certain reordering of instructions for optimization but ensures that memory consistency errors do not occur.

6. Explain the differences between synchronized and Lock in Java.

Synchronized:

Built-in monitor lock.
Simple to use (block or method level).
Automatically releases the lock.
No timeout feature.

public synchronized void method() { // synchronized method } public void method() { synchronized(this) { // synchronized block } }

Lock (from java.util.concurrent.locks package):

More flexible and sophisticated.
Explicit lock and unlock calls.
Supports try-lock with timeout, fairness policies, and multiple conditions.

import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; private final Lock lock = new ReentrantLock(); public void method() { lock.lock(); try { // critical section } finally { lock.unlock(); } }

7. Explain Spring Boot’s support for microservices architecture.

Spring Boot supports microservices architecture by providing features such as

Embedded servers,
Simplified dependency management,
Production-ready metrics.

It facilitates the creation of standalone, production-grade Spring-based applications with minimal configuration.

8. What is Spring Boot DevTools, and how does it improve the development process?

Spring Boot DevTools is a set of tools that enhances the development process by enabling automatic restarts, live reloads, and configurations for a more efficient workflow. It helps developers by reducing the time needed to see the effects of code changes, thereby improving productivity and speeding up the development cycle.

9. How do you handle authentication and authorization in a full-stack React JS + Spring Boot application?

Authentication and Authorization in React JS + Spring Boot:

User Registration and Login:

Back-end (Spring Boot):

Create REST endpoints for /register and /login.
Use Spring Security for authentication.
Implement JWT tokens for session management.

Front-end (React JS):

Create registration and login forms.
Use Axios or Fetch to send POST requests to the back-end.
Store the JWT token in localStorage or sessionStorage

Authorization:

Back-end (Spring Boot):

Secure routes using Spring Security with annotations like @PreAuthorize.
Validate JWT tokens in requests to protected endpoints.

Front-end (React JS):

Protect routes using React Router.
Check for the JWT token before rendering protected components

10. Explain event delegation.

Event delegation is a technique of leveraging event bubbling to handle events at a higher level in the DOM tree.

11. How can you manage memory using the weakref module in Python?

The weakref module provides tools for creating weak references to objects. A weak reference allows the referenced object to be garbage collected if there are no strong references to it, thus helping in managing memory more efficiently.

12. What are metaclasses in Python, and how are they used?

A metaclass in Python is a class of a class that defines how a class behaves. Metaclasses allow customization of class creation by overriding methods like __new__ and __init__. The most common use cases are for logging, enforcing coding standards, or registering classes.

13. What is a RESTful API?

A RESTful API adheres to REST (Representational State Transfer) principles, using standard HTTP methods like GET, POST, PUT, DELETE. It involves stateless interactions and uses URLs to access resources.

14. Explain the difference between SQL and NoSQL databases.

SQL Databases: Relational, structured schema, use SQL for queries (e.g., MySQL, PostgreSQL).

NoSQL Databases: Non-relational, flexible schema, designed for scalability (e.g., MongoDB, Cassandra).

15. Explain the concept of middleware in Express.js.

Middleware functions in Express.js are functions that execute during the request-response cycle. They can modify the request or response, end the request-response cycle, or call the next middleware function.

16. How do you handle state management in a React application?

State management in React can be handled using:

Local State:Using useState or useReducer hooks.
Context API: For prop drilling solutions.
State Management Libraries: Like Redux or MobX for larger applications.

17. Explain the purpose of Docker in development.

Docker is a containerization platform that packages applications and their dependencies into containers. This ensures consistency across development, testing, and production environments and simplifies deployment.

18. What is the role of a Webpack in modern web development?

Webpack is a module bundler for JavaScript applications. It bundles JavaScript files and other assets (like CSS, images) into a single file or a set of files, optimizing them for production.

19. How do you secure a RESTful API?

Authentication: Using JWTs, OAuth.
Authorization: Role-based access control.
Input Validation: Sanitizing and validating user inputs.
HTTPS: Encrypting data in transit.
Rate Limiting: Preventing abuse by limiting the number of requests.

20. What is CORS and why is it important?

CORS (Cross-Origin Resource Sharing) is a security feature implemented by browsers to prevent web pages from making requests to a different domain. It requires the server to include specific headers to allow cross-origin requests.

21. What is the purpose of a load balancer?

A load balancer distributes incoming network traffic across multiple servers to ensure no single server becomes overwhelmed, enhancing the availability and reliability of applications.

22. Explain how you would optimize a web application’s performance.

Front-end Optimization: Minimize and bundle CSS and JavaScript, use lazy loading for images, and optimize images.
Back-end Optimization: Optimize database queries, use caching mechanisms (e.g., Redis), and implement efficient data structures and algorithms.
Network Optimization: Use CDNs (Content Delivery Networks) to deliver content faster and enable HTTP/2 for improved performance.

23. How do you secure a RESTful API?

Authentication: Using JWTs, OAuth.
Authorization: Role-based access control.

Input Validation: Sanitizing and validating user inputs.

HTTPS: Encrypting data in transit.

Rate Limiting: Preventing abuse by limiting the number of requests.

24. What is the virtual DOM in React?

The virtual DOM is a lightweight, in-memory representation of the real DOM. React uses it to optimize updates by only rendering parts of the DOM that have changed, improving performance.

25. How do you implement caching in a web application?

Client-Side Caching: Using browser cache.

Server-Side Caching: Using technologies like Redis, Memcached.

HTTP Caching: Using cache headers (e.g., Cache-Control, ETag).

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Capgemini Full Stack Interview Questions and Answers