The Hi-tech Robotic Systemz Java Software Developer Interview Questions and Answers

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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Building small UI screen application in 1 hr for frontend developer

Q1. Graph traversal question
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Q2. React js questions
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Q3. Javascript output guessing question
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Q1. Define Object-oriented programming
Ans. 
Object-oriented programming is a programming paradigm based on the concept of objects, which can contain data and code.
• Objects are instances of classes, which define the structure and behavior of the objects.

• Encapsulation, inheritance, and polymorphism are key principles of OOP.

• Example: In Java, a class 'Car' can have attributes like 'color' and 'model', and methods like 'drive' and 'stop'.
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Q2. What is Default method in Java?
Ans. 
Default method in Java is a method defined in an interface with a default implementation.
• Introduced in Java 8 to allow adding new methods to interfaces without breaking existing implementations

• Default methods are declared with the 'default' keyword

• They can be overridden in implementing classes if needed
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Q1. 1. What are the advantages of Microservices?
Ans. 
Microservices offer advantages such as scalability, flexibility, and easier maintenance.
• Scalability: Microservices allow for individual components to be scaled independently, making it easier to handle high traffic.

• Flexibility: Microservices can be developed and deployed independently, allowing for faster development and deployment cycles.

• Easier maintenance: Microservices are smaller and more focused, making it easier ...read more
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Q2. 2. What are the disadvantages?
Ans. 
Disadvantages of what? Please specify.
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Q3. 3. How hashmap internally works?
Ans. 
HashMap is a data structure that stores key-value pairs and uses hashing to retrieve values quickly.
• HashMap uses hashing to store and retrieve values quickly

• It uses an array of buckets to store key-value pairs

• The hash code of the key is used to determine the bucket where the key-value pair is stored

• If two keys have the same hash code, they are stored in the same bucket as a linked list

• When retrieving a value, the hash ...read more
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Q4. 4.Linked list Vs Arraylist
Ans. 
Linked list is dynamic and efficient for insertion/deletion, while ArrayList is faster for random access.
• Linked list uses pointers to connect nodes, while ArrayList uses an underlying array.

• Linked list is better for frequent insertion/deletion, while ArrayList is better for frequent random access.

• Linked list has O(1) time complexity for insertion/deletion, while ArrayList has O(n) time complexity.

• Example: Linked list i...read more
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Q5. 5. Write a program to get the middle of the linked list in a single iteration? Ans - Two pointers , slow fast
Ans. 
Program to get the middle of a linked list in a single iteration using two pointers.
• Use two pointers, slow and fast, to traverse the linked list

• Move slow pointer one step at a time and fast pointer two steps at a time

• When fast pointer reaches the end, slow pointer will be at the middle node
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Q6. 6. Stack peek vs Stack pop?
Ans. 
Stack peek returns the top element without removing it, while stack pop removes and returns the top element.
• Stack peek is used to check the top element of the stack without removing it.

• Stack pop is used to remove and return the top element of the stack.

• Both methods operate on the top element of the stack.
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Q7. 7. RequestMapping vs Postmapping?
Ans. 
RequestMapping is used for all HTTP methods while PostMapping is specifically for POST requests.
• RequestMapping is a general-purpose annotation for mapping HTTP requests to handler methods.

• PostMapping is a specialized version of RequestMapping that only maps POST requests.

• RequestMapping can be used for GET, POST, PUT, DELETE, and other HTTP methods.

• PostMapping is useful when you want to handle only POST requests and ign...read more
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Q8. 8. Singleton in java . And how singleton can be broken
Ans. 
Singleton is a design pattern that restricts the instantiation of a class to one object.
• Singleton pattern is used when we need to ensure that only one instance of a class is created and used throughout the application.

• To implement Singleton, we make the constructor private and provide a static method to get the instance of the class.

• Singleton can be broken by using reflection, serialization, and cloning.

• Reflection can ...read more
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Q9. 9. What is @SpringBootApplication?
Ans. 
A convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.
• Used to bootstrap a Spring Boot application.

• Automatically configures the Spring application based on the dependencies added to the classpath.

• Scans the package and its sub-packages for components and services.

• Example: @SpringBootApplication public class MyApplication { public static void main(String[] args) { SpringApplic
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Q10. 10. RestController vs Controller?
Ans. 
RestController is used for RESTful web services while Controller is used for traditional web applications.
• RestController returns data in JSON or XML format while Controller returns data in HTML format.

• RestController uses @RestController annotation while Controller uses @Controller annotation.

• RestController is used for building RESTful web services while Controller is used for building traditional web applications.

• RestC...read more
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Q11. 11. Why do we need maven clean and install?
Ans. 
Maven clean removes target directory and install compiles and packages the project
• Maven clean removes the target directory and all the compiled classes and resources

• Maven install compiles and packages the project and installs the resulting artifact into the local repository

• Maven clean and install together ensure that the project is built from scratch and all dependencies are resolved

• Useful when there are changes in the
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Q12. 12. How to switch from one branch to other in git?
Ans. 
To switch from one branch to another in git, use the 'git checkout' command.
• Use 'git checkout' followed by the name of the branch you want to switch to.

• Make sure to commit or stash any changes before switching branches.

• Example: 'git checkout new-branch'
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Q1. 1. How do you secure your APIs?
Ans. 
APIs can be secured using various methods such as authentication, encryption, rate limiting, and input validation.
• Implement authentication using OAuth or JWT

• Use HTTPS encryption to protect data in transit

• Implement rate limiting to prevent DDoS attacks

• Validate input data to prevent injection attacks

• Regularly update and patch software to prevent vulnerabilities
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Q2. 2. What is deadlock? How to resolve it?
Ans. 
Deadlock is a situation where two or more threads are blocked and waiting for each other to release resources.
• Deadlock occurs when two or more threads are waiting for each other to release resources.

• It can be resolved by using techniques like resource allocation graph, timeout, and prevention.

• Prevention can be done by avoiding circular wait, hold and wait, and no preemption.

• Example: Thread A holds resource X and waits ...read more
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Q3. 3. What is spring filter ?
Ans. 
Spring filter is an interface used to intercept HTTP requests and responses.
• Spring filter is used to perform tasks such as logging, security, and caching.

• It can be used to modify the request or response before it reaches the controller.

• Examples of Spring filters include CharacterEncodingFilter, CorsFilter, and CsrfFilter.
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Q4. 4. What is future object in java?
Ans. 
A Future object represents the result of an asynchronous computation in Java.
• Future objects are used to retrieve the result of an asynchronous computation when it becomes available.

• They provide a way to check if the computation is complete, cancel the computation, and retrieve the result.

• They are commonly used in multithreaded programming and in Java's Executor framework.

• Example: Future future = executor.submit(new Cal...read more
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Q5. 5. Lifecycle of object in hibernate ?
Ans. 
Hibernate manages object lifecycle through three states: transient, persistent, and detached.
• When an object is created, it is in the transient state.

• When the object is saved using session.save() method, it becomes persistent.

• When the session is closed or the object is explicitly detached using session.evict() method, it becomes detached.

• Detached objects can be re-attached to a new session using session.update() or sess...read more
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Q6. 6. Save vs Persist in hibernate ?
Ans. 
Save() method inserts a new record into the database, while persist() method can also be used to update an existing record.
• save() method is used to insert a new record into the database

• persist() method can also be used to insert a new record, but it can also be used to update an existing record

• save() method returns the generated ID immediately, while persist() method does not

• save() method can be called outside of a tra...read more
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Q7. 7. Merge intervals problem in java
Ans. 
Merge overlapping intervals in Java
• Sort the intervals based on their start time

• Iterate through the intervals and merge overlapping ones

• Use a stack to keep track of merged intervals
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Q8. 8. Scopes of bean ?
Ans. 
Scopes of bean refer to the visibility and lifecycle of a bean in a Spring application.
• There are four scopes of bean in Spring: singleton, prototype, request, and session.

• Singleton scope creates only one instance of a bean and is the default scope.

• Prototype scope creates a new instance of a bean every time it is requested.

• Request scope creates a new instance of a bean for each HTTP request.

• Session scope creates a new i...read more
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Q1. You have a hotel and how will you create a complete schema for hotel
Ans. 
To create a complete schema for a hotel, you need to consider various entities like rooms, guests, reservations, staff, amenities, etc.
• Entities to include: rooms, guests, reservations, staff, amenities, invoices, payments

• Relationships between entities: guest stays in a room, staff manages reservations, amenities are available in rooms

• Attributes for each entity: room number, guest name, reservation date, staff ID, ameni
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Q1. They will ask you about core java
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Array duplicates and burn binary tree

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