Dotsquares Fullstack Java Developer Interview Questions and Answers

Q1. What is Middleware?
Ans. 
Middleware is software that acts as a bridge between an application's front end and back end, allowing them to communicate and interact.
• Middleware can handle tasks such as authentication, logging, error handling, and routing.

• It can be used to modify incoming requests or outgoing responses.

• Examples of middleware include Express.js middleware in Node.js applications and ASP.NET middleware in .NET applications.
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Q2. What is Dependency Injection ?
Ans. 
Dependency Injection is a design pattern where components are given their dependencies rather than creating them internally.
• Allows for better code reusability and testability

• Reduces coupling between components

• Promotes separation of concerns

• Examples: Constructor Injection, Setter Injection, Interface Injection
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Q3. What is Solid Principles ?
Ans. 
Solid Principles are a set of five design principles for writing clean, maintainable, and scalable code.
• Single Responsibility Principle: A class should have only one reason to change.

• Open/Closed Principle: Classes should be open for extension but closed for modification.

• Liskov Substitution Principle: Objects of a superclass should be replaceable with objects of its subclasses without affecting the program's correctness...read more
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Q1. Internal working of hashmap
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HashMap is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values.
• HashMap internally uses an array of linked lists to store key-value pairs.

• When a key-value pair is added, the key is hashed to find the index in the array where it will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• HashMap allows one null key and multiple null values.

• Th...read more
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Q2. What is singleton class and its implementation
Ans. 
Singleton class is a class that can only have one instance and provides a global point of access to it.
• Singleton class restricts the instantiation of a class to one object.

• It provides a way to access its unique instance globally.

• Commonly used in scenarios where only one instance of a class is needed, such as database connections or thread pools.
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Q3. Find all the pairs with given sum coding
Ans. 
The task is to find all pairs in an array that add up to a given sum.
• Iterate through the array and store each element in a hash set.

• For each element, check if the difference between the sum and the element exists in the hash set.

• If it does, add the pair to the result list.
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Q1. Redis cache and distributed cache
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Q2. CORS , Trigger, OOPS , Queries
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One question on Java on reversing only the numbers in an array
One question on React to build search component

Q1. Fundamentals in java, react and spring
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Q1. Middleware in nodejs and uses
Ans. 
Middleware in Node.js is a function that has access to the request and response objects, and can modify or terminate the request-response cycle.
• Middleware functions are executed sequentially in the order they are defined.

• They can be used for tasks such as logging, authentication, error handling, etc.

• Example: Express.js uses middleware extensively for handling requests.
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Q1. Differences between promises and observables
Ans. 
Promises are used for a single async operation while observables handle multiple async operations and can be cancelled.
• Promises are eager, meaning they start immediately upon creation.

• Observables are lazy, meaning they only start when subscribed to.

• Promises can only handle a single value or error, while observables can handle multiple values over time.

• Observables can be cancelled, while promises cannot be cancelled.

• Pro...read more
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Q2. Angular vs react differences
Ans. 
Angular and React are both popular front-end frameworks, but they have some key differences in terms of architecture, syntax, and ecosystem.
• Angular is a full-fledged framework with a steep learning curve, while React is a library that is more flexible and easier to learn.

• Angular uses two-way data binding, while React uses one-way data flow.

• Angular has a more opinionated architecture and provides more out-of-the-box fea...read more
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Basic level of maths and some coding related questions

On current affairs and daily routine

Two basic questions related to pattern string array etc

Q1. This is final step and would be conducted in their office itself
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Q2. It will include some oops questions bond discussion and questions on Resume
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