CoinDCX Software Development Engineer 1 Interview Questions and Answers

Q1. Difference between static and final
Ans. 
Static is used to define class-level variables and methods, while final is used to define constants that cannot be changed.
• Static variables belong to the class itself, while final variables are constants that cannot be modified.

• Static methods can be called without creating an instance of the class, while final methods cannot be overridden.

• Static variables are shared among all instances of a class, while final variables...read more
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Q2. ArraysList vs LinkedList
Ans. 
ArrayList is better for random access, LinkedList is better for frequent insertions/deletions.
• ArrayList uses dynamic array to store elements, LinkedList uses doubly linked list.

• ArrayList provides fast random access to elements using index, LinkedList provides fast insertion/deletion at any position.

• Example: ArrayList is suitable for scenarios where random access is required like searching, LinkedList is suitable for sc...read more
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Q3. Describe Java8 Features
Ans. 
Java8 introduced several new features including lambda expressions, functional interfaces, streams, and default methods.
• Lambda expressions allow you to write code in a more concise and readable way.

• Functional interfaces are interfaces with a single abstract method, which can be implemented using lambda expressions.

• Streams provide a way to work with collections of objects in a functional style.

• Default methods allow inte...read more
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Q4. Gave one scenario to solve using streams in java8
Ans. 
Using streams in Java 8 to filter and map a list of numbers
• Create a list of numbers

• Use stream to filter out even numbers

• Use map to square each number

• Collect the results into a new list
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Q5. Multithreading- Write program to print even and odd numbers from 1 to 20 using 2 threads. 1 thread will responsible for printing even and another for Odd. And print in such a manner it should be alternate....read more
Ans. 
Program to print even and odd numbers from 1 to 20 using 2 threads alternately.
• Create two threads, one for printing even numbers and one for printing odd numbers.

• Use wait(), notify(), and notifyAll() to ensure alternate printing.

• Ensure synchronization between the two threads to avoid race conditions.

• Example: Thread 1 prints even numbers (2, 4, 6, ...) and Thread 2 prints odd numbers (1, 3, 5, ...).
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Q6. Why strings immutable
Ans. 
Strings are immutable to ensure data integrity and security.
• Immutable strings prevent accidental changes to data

• Immutable strings allow for safe sharing of data between different parts of a program

• Immutable strings help prevent security vulnerabilities like SQL injection attacks
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Q7. Outer Join SQL query
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Q8. What is the purpose of using default methods in java8?
Ans. 
Default methods in Java 8 allow interfaces to have method implementations, enabling backward compatibility and reducing code duplication.
• Default methods were introduced in Java 8 to provide a way to add new methods to interfaces without breaking existing implementations.

• They allow interfaces to have method implementations, which was not possible before Java 8.

• Default methods can be overridden in implementing classes to...read more
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Q1. 1 coding problem related to Anagrams
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Q2. 1 Java8 streams problem
Ans. 
Using Java8 streams to solve a problem
• Use stream() method to convert a collection into a stream

• Use filter() method to filter elements based on a condition

• Use map() method to transform elements

• Use collect() method to collect the elements into a new collection
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Q3. What are checked exceptions
Ans. 
Checked exceptions are exceptions that must be either caught or declared in the method signature.
• Checked exceptions are subclasses of Exception (excluding RuntimeException and its subclasses)

• Checked exceptions must be either caught using try-catch block or declared in the method signature using 'throws' keyword

• Examples of checked exceptions in Java include IOException, SQLException, and ClassNotFoundException
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Q4. Purpose of @SpringBootApplication annotation?
Ans. 
Annotation used to mark a class as a Spring Boot application
• Combines @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations

• Used to bootstrap and launch a Spring application

• Automatically scans for Spring components in the package and sub-packages
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Q5. Use of @Qualifier
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Annotation used in Spring to specify which bean to autowire
• Used to disambiguate when multiple beans of the same type are present

• Can be used with @Autowired to specify which bean to inject

• Helps in resolving dependencies when multiple beans of the same type are available
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Q6. What are microservices?
Ans. 
Microservices are a software development technique where an application is composed of small, independent services that communicate with each other.
• Microservices are designed to be small, focused on specific tasks, and independently deployable.

• Each microservice typically runs its own process and communicates with other services through APIs.

• Microservices allow for easier scalability, flexibility, and maintenance compar...read more
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Q7. Design patterns
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Q8. How microservices communicate with each other
Ans. 
Microservices communicate with each other through APIs, messaging queues, or service meshes.
• APIs: Microservices can communicate with each other by exposing APIs that allow them to send and receive data.

• Messaging queues: Microservices can use messaging queues like RabbitMQ or Kafka to send messages to each other asynchronously.

• Service meshes: Microservices can communicate through a service mesh like Istio, which handles...read more
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Q1. Asked about projects.
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Q2. Complete flow and business use case of the project
Ans. 
The project involves creating a web-based platform for online shopping with features like user registration, product browsing, shopping cart, and payment processing.
• User registers on the platform with personal information

• User browses products by category or search

• User adds products to the shopping cart

• User proceeds to checkout and makes payment

• Order is confirmed and user receives a confirmation email
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Q3. Interviewer was more concerned about matching the tech stack with job description
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It included mcqs and multiple coding questions.

Q1. Yours technical skillls related questions
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Q2. Managerial questions
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Q1. What are React Queries?
Ans. 
React Queries are a library for managing server state in React applications.
• React Queries provide a way to fetch and cache data from an API in React components.

• They offer features like caching, background fetching, and automatic refetching.

• React Queries can handle complex data fetching requirements, such as pagination and infinite scrolling.
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Q2. Can useEffect() hook run twice?
Ans. 
Yes, useEffect() hook can run twice under certain conditions.
• useEffect() hook can run twice if the dependencies array changes between renders.

• This can happen if the dependencies array contains values that change frequently.

• For example, if a state variable is included in the dependencies array and it is updated in the component, useEffect() will run again.
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Written test was in python where we have output based questions

Q1. Move zeros to the end of the array
Ans. 
Move all zeros in an array of strings to the end.
• Iterate through the array and move all zeros to the end by swapping with non-zero elements.

• Maintain a pointer to keep track of the position to swap with zeros.

• Example: Input: ['a', 'b', 'c', '0', 'd', '0'], Output: ['a', 'b', 'c', 'd', '0', '0']
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Q1. Basic questions of angular and javascript.
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Q2. Es6 feature , typescript features
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Q3. Promise, observable, focus on syntax of every thing like interceptor, routing, gaurd and all .
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Q1. Behaviour subject, subject, life cycle hooks
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Q2. This round was not very easy in my case.
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Q3. Be prepared for array and object of array questions. Like sorting, searching, filtering , any logic .
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Q1. Basic HR questions and managerial round. Not being hard . But learn about your project and past organisation
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DSA, SUM Practice, DSA SUM

DSA Sum Practice DSA Sum

Q1. 2 sum problem on number
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Q1. Json data manipulation
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Q1. Normal hr question
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