Infosys Fullstack Java Application Developer Interview Questions and Answers

Q1. Types of cloning in java
Ans. 
There are two types of cloning in Java: Shallow and Deep cloning.
• Shallow cloning creates a new object with the same field values as the original object, but the fields refer to the same objects as the original object.

• Deep cloning creates a new object with the same field values as the original object, but the fields refer to new copies of the original objects.

• Shallow cloning can be done using the clone() method, while d...read more
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Q2. What are idempotent methods in rest
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Idempotent methods in REST are HTTP methods that can be repeated multiple times without changing the result beyond the initial application.
• Idempotent methods are safe to retry or repeat without causing unintended side effects.

• GET, HEAD, PUT, and DELETE are idempotent methods.

• POST is not idempotent because it creates a new resource with a new URI each time it is called.

• Idempotency is important for ensuring the reliabili
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Q3. Difference between put and post
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PUT is used to update an existing resource, while POST is used to create a new resource.
• PUT replaces the entire resource with the new data, while POST appends the new data to the existing resource.

• PUT is idempotent, meaning multiple identical requests will have the same effect as a single request, while POST is not.

• PUT requires the client to specify the resource ID in the request URL, while POST does not.

• Example: PUT /...read more
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Q4. Describe caching mechanism in hibernate
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Hibernate provides two levels of caching: first-level cache and second-level cache.
• First-level cache is enabled by default and is associated with a Session object.

• Second-level cache is optional and can be configured to use different caching providers like Ehcache, Hazelcast, etc.

• Caching can improve application performance by reducing the number of database queries.

• Caching can also cause data inconsistency issues if not...read more
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Q5. Association between hashcode and equals to method
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Hashcode and equals method are related in Java to ensure proper object comparison and hashing.
• The hashcode method returns an integer value that represents the object's unique identifier.

• The equals method compares two objects for equality and returns a boolean value.

• If two objects are equal, their hashcodes must be equal as well.

• If two objects have the same hashcode, it does not necessarily mean they are equal.

• It is imp...read more
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Q6. What is the logging framework you used and errors it highlights
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Q7. Write a program to get duplicate element in array list
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Program to find duplicate elements in an array list
• Create a HashSet to store unique elements

• Loop through the array list and add each element to the HashSet

• If an element already exists in the HashSet, it is a duplicate

• Add the duplicate element to another list or print it
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Q8. Describe cascading in hibernate
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Cascading in Hibernate refers to the ability to propagate the state of an entity to its associated entities.
• Cascading is used to automatically persist, update, or delete associated entities when the state of the parent entity changes.

• There are different types of cascading options available in Hibernate, such as ALL, PERSIST, MERGE, REMOVE, and REFRESH.

• For example, if a parent entity has a collection of child entities a...read more
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Q9. Difference between get session and load in hibernate
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getSession() retrieves the current session while load() method loads the object by its identifier.
• getSession() method is used to retrieve the current session from the session factory.

• load() method is used to load the object by its identifier.

• getSession() method returns null if there is no current session.

• load() method throws an exception if the object is not found in the database.

• getSession() method is used for read an...read more
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Q10. What is hql? what are it's benefits?
Ans. 
HQL stands for Hibernate Query Language. It is an object-oriented query language used to retrieve data from a database.
• HQL is similar to SQL but uses object-oriented concepts like inheritance, polymorphism, and association.

• It is database independent and can be used with any database supported by Hibernate.

• HQL queries are compiled to SQL queries at runtime, which makes it more efficient than using SQL directly.

• It suppor...read more
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Q11. How to do xml validation
Ans. 
XML validation can be done using XML Schema Definition (XSD) or Document Type Definition (DTD).
• XSD is the preferred method for XML validation as it provides more features and is easier to use.

• DTD is an older method and has limited features compared to XSD.

• XML validation can be done using tools like XMLSpy, Notepad++, and online validators like W3C Markup Validation Service.

• Validation can be done programmatically using ...read more
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Q12. What are methods of object class
Ans. 
Methods of Object class in Java
• toString() - returns a string representation of the object

• equals(Object obj) - checks if two objects are equal

• hashCode() - returns a hash code value for the object

• getClass() - returns the runtime class of the object

• wait() - causes the current thread to wait

• notify() - wakes up a single thread that is waiting on the object

• notifyAll() - wakes up all threads that are waiting on the object
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Q13. How to secure rest api
Ans. 
Secure REST API using authentication, encryption, and authorization.
• Use HTTPS protocol to encrypt data in transit

• Implement authentication using tokens or OAuth2

• Implement authorization using roles and permissions

• Use input validation and output encoding to prevent injection attacks

• Implement rate limiting to prevent DDoS attacks
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Q14. Which authentication methods used to secure rest api
Ans. 
Various authentication methods can be used to secure REST API, including OAuth, JWT, Basic Authentication, and API Keys.
• OAuth is a popular authentication method that allows users to grant access to third-party applications without sharing their credentials.

• JWT (JSON Web Tokens) is a stateless authentication mechanism that uses a token to authenticate users.

• Basic Authentication uses a username and password to authentica...read more
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Q15. How do we handle exceptions in rest
Ans. 
Exceptions in REST are handled using try-catch blocks and HTTP status codes.
• Use try-catch blocks to catch exceptions thrown by the application

• Map exceptions to appropriate HTTP status codes

• Return error messages in the response body

• Use global exception handlers to handle uncaught exceptions

• Avoid returning sensitive information in error messages
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Q16. Which data structure used in array and hashmap
Ans. 
Arrays use a linear data structure while HashMap uses a key-value pair data structure.
• Arrays are indexed collections of elements of the same data type.

• HashMaps store key-value pairs and allow for fast retrieval of values based on their keys.

• Arrays have a fixed size while HashMaps can dynamically resize.

• Arrays are more efficient for simple data structures while HashMaps are better for complex data structures.
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Q17. What is sql injection
Ans. 
SQL injection is a type of cyber attack where malicious SQL statements are inserted into an entry field to manipulate the database.
• SQL injection can be used to steal sensitive information, modify or delete data, or even take control of the entire database.

• It can be prevented by using parameterized queries, input validation, and limiting user privileges.

• Example: Entering ' OR 1=1;--' in a login form can bypass authentic...read more
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Q18. What is synchronized key word
Ans. 
Synchronized keyword is used to control access to shared resources in a multithreaded environment.
• It ensures that only one thread can access the shared resource at a time.

• It can be applied to methods or blocks of code.

• It can cause performance issues if used excessively.

• Example: synchronized void myMethod() { //code }

• Example: synchronized(this) { //code }
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Q19. Difference between string and string buffer
Ans. 
String is immutable while StringBuffer is mutable.
• StringBuffer is faster for concatenation operations.

• StringBuffer has methods to modify the string while String does not.

• StringBuffer is thread-safe while String is not.

• Example: String str = "hello"; StringBuffer sb = new StringBuffer(str); sb.append(" world");

• Example: String str = "hello"; str.concat(" world"); // returns a new string, original string is not modified.
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Q20. Design patterns in java
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Design patterns are reusable solutions to common software problems.
• Design patterns help in creating flexible, reusable, and maintainable code.

• Some popular design patterns in Java are Singleton, Factory, Observer, and Decorator.

• Singleton pattern ensures that only one instance of a class is created.

• Factory pattern provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objec...read more
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Q21. Describe reflection api in java
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Reflection API in Java allows inspection and modification of runtime behavior of a program.
• Reflection API provides classes like Class, Method, Field, Constructor, etc. to inspect and modify the behavior of a program at runtime.

• It can be used to access private fields and methods of a class.

• It can be used to create new instances of a class dynamically.

• It can be used to invoke methods of a class dynamically.

• It can be used...read more
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Coding is little difficult so please go through logic

Q1. The interview is based on the skills you mentioned in resume
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Q2. What is the use of Java
Ans. 
Java is a versatile programming language used for developing a wide range of applications, from web and mobile apps to enterprise systems.
• Java is used for developing web applications, mobile applications, desktop applications, and enterprise systems.

• It is commonly used in backend development for server-side programming.

• Java is also used in game development, scientific applications, and big data processing.

• It is platfor...read more
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Q1. About company and your skills
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Q2. Java full stack developet
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Normal Gaming Question and Aptitude

Q1. Introduce yourself. Tell me Something about your Project.
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Q2. Technical Question from Java.
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Def factorial_iterative(n):
result = 1
for i in range(1, n + 1):
result *= i
return result

Q1. Tell me about internal working of JVM
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Q2. Tell me about SAGA pattern in Microservices
Ans. 
SAGA pattern is a design pattern used in microservices architecture to manage distributed transactions.
• SAGA pattern breaks down a long-running transaction into a series of smaller, independent transactions.

• Each step in the SAGA pattern is a separate service that communicates with other services through events.

• If a step fails, compensating transactions are executed to rollback the changes made by previous steps.

• Example:...read more
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Q1. Tell me about your current project structure
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Q2. What is an API , how would you secure an API
Ans. 
API stands for Application Programming Interface. It defines the methods and data formats that applications can use to communicate with each other.
• API is a set of rules and protocols that allows different software applications to communicate with each other.

• To secure an API, you can use authentication methods like OAuth, API keys, or JWT tokens.

• Implementing encryption (HTTPS) and rate limiting can also enhance API secu...read more
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Q1. Why do you want to relocate to Bangalore
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Q2. Tell me about one instance where you faced pressure and how did you overcome ?
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Q1. Basic js question on hoisting, closure, promises
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Q1. Basic resume based
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Q1. Salary discussion -- HR never responded
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Q1. Java Basic questions
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Q2. SpringBoot Basic questions
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Q3. Simple DSA problem: "introduction" find duplicate characters
Ans. 
Find duplicate characters in a given array of strings
• Iterate through each string in the array

• For each string, iterate through each character and store the count in a hashmap

• If the count of any character is greater than 1, it is a duplicate
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Q4. Write code for REST API using spring boot, include all annotation
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Code for REST API using Spring Boot with annotations
• Use @RestController annotation to define the class as a REST controller

• Use @RequestMapping annotation to map HTTP requests to handler methods

• Use @GetMapping, @PostMapping, @PutMapping, @DeleteMapping annotations for specific HTTP methods

• Use @PathVariable annotation to extract values from the URI

• Use @RequestBody annotation to bind HTTP request body to a method paramete
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