Persistent Systems Interview Questions, Process, and Tips

Q1. What is the architecture of the Java Virtual Machine (JVM)?
Ans. 
The Java Virtual Machine (JVM) is an abstract computing machine that enables a computer to run Java programs.
• JVM is platform-independent and converts Java bytecode into machine code.

• It consists of class loader, runtime data areas, execution engine, and native method interface.

• JVM memory is divided into method area, heap, stack, and PC register.

• Examples of JVM implementations include Oracle HotSpot, OpenJ9, and GraalVM.
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Q2. What is the default connection pooling in Spring Boot, and how can it be customized?
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The default connection pooling in Spring Boot is HikariCP, which can be customized through properties in the application.properties file.
• HikariCP is the default connection pooling library in Spring Boot, known for its high performance and low overhead.

• To customize the connection pooling, you can modify properties like 'spring.datasource.hikari.*' in the application.properties file.

• For example, you can set maximum pool ...read more
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Q3. What are the best practices for optimizing a Spring Boot application?
Ans. 
Best practices for optimizing a Spring Boot application
• Use Spring Boot Actuator to monitor and manage application performance

• Implement caching mechanisms like Spring Cache to reduce database calls

• Optimize database queries and indexes for better performance

• Use asynchronous processing with Spring's @Async annotation for non-blocking operations

• Profile and analyze application performance using tools like VisualVM or JProfi
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Q4. What is a heap dump, and how can it be used to identify memory leaks?
Ans. 
A heap dump is a snapshot of the memory usage of a Java application at a specific point in time.
• Heap dumps can be generated using tools like jmap or VisualVM.

• They provide detailed information about objects in memory, their sizes, and references.

• Analyzing a heap dump can help identify memory leaks by pinpointing objects that are consuming excessive memory.

• Common signs of memory leaks in a heap dump include a large numbe...read more
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Q5. How can you diagonally iterate through and print the elements of a 2D array?program
Ans. 
Diagonally iterate through and print elements of a 2D array of strings.
• Use nested loops to iterate through rows and columns of the 2D array.

• Calculate the diagonal elements by incrementing row and column indices together.

• Print the elements as you iterate through the diagonal of the array.
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It's walkin, so they conducted 1 technical mcqs round.

Q1. Multi threading
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Q2. Internal working of hashmap
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HashMap in Java is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values based on keys.
• HashMap uses an array of buckets to store key-value pairs.

• Keys are hashed to determine the index in the array where the key-value pair will be stored.

• In case of hash collisions, a linked list or a balanced tree is used to store multiple key-value pairs in the same bucket.

• HashMap allows null keys...read more
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Q3. Spring batch related
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Q4. Non repeating characters in a array
Ans. 
Function to find and return all non-repeating characters in an array of strings.
• Iterate through the array and count the occurrences of each character using a HashMap.

• Then iterate through the array again and check if the count of each character is 1, if so add it to the result list.

• Return the list of non-repeating characters.
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Q5. 3rd highest salary
Ans. 
To find the 3rd highest salary in a database, we can use a SQL query with the 'LIMIT' and 'OFFSET' keywords.
• Use a SQL query with 'ORDER BY salary DESC' to sort the salaries in descending order.

• Use 'LIMIT 1 OFFSET 2' to skip the first two highest salaries and retrieve the third highest salary.

• Example: SELECT salary FROM employees ORDER BY salary DESC LIMIT 1 OFFSET 2;
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Q6. Qualifier vs primary
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A qualifier in Java is used to specify additional information about a primary, which is the main data type or variable.
• A primary in Java is the main data type or variable, while a qualifier provides additional information about the primary.

• Qualifiers can be used to modify the behavior or characteristics of a primary.

• For example, in Java, 'final' is a qualifier that can be used to make a variable constant.
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Q7. Controller vs restcontroller
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The main difference is that @RestController is a specialized version of @Controller that is used for RESTful web services.
• Both @Controller and @RestController are used in Spring MVC to handle HTTP requests, but @RestController is specifically used for RESTful web services.

• @Controller is used to create web pages, while @RestController is used to return data in JSON or XML format.

• @RestController is a convenience annotati...read more
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Q8. Spring boot annotataions
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Q9. Oops concepts with examples
Ans. 
OOP concepts include inheritance, encapsulation, polymorphism, and abstraction.
• Inheritance: Allows a class to inherit properties and behavior from another class. Example: class Dog extends Animal.

• Encapsulation: Bundling data and methods that operate on the data into a single unit. Example: private variables with public getter and setter methods.

• Polymorphism: Ability for objects to be treated as instances of their paren...read more
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Q10. Spring batch configuration
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Q11. They covered all java, spring and Microservices
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Q1. Microservices architecture
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Q2. How do Microservices communicate
Ans. 
Microservices communicate with each other through various communication protocols like HTTP, messaging queues, and gRPC.
• Microservices can communicate over HTTP using RESTful APIs.

• Messaging queues like RabbitMQ or Kafka can be used for asynchronous communication between microservices.

• gRPC is a high-performance, open-source RPC framework that can be used for communication between microservices.

• Service discovery mechanism...read more
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Q3. How to access the Microservice end point
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Microservice endpoints can be accessed using HTTP requests with the appropriate URL
• Use HTTP methods like GET, POST, PUT, DELETE to interact with the microservice

• Construct the URL with the base URL of the microservice and the specific endpoint path

• Include any necessary headers or parameters in the request for authentication or data filtering
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Q4. Why we use microservices
Ans. 
Microservices allow for modular, scalable, and flexible software development by breaking down applications into smaller, independent services.
• Microservices enable easier maintenance and updates as each service can be developed, deployed, and scaled independently.

• They improve fault isolation, as failures in one service do not necessarily affect the entire application.

• Microservices promote agility and faster time-to-mark...read more
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Q1. Core Java questions and multithreading basics like executor service
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Q2. Spring boot error handling, simple questions on distributed systems
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Q3. Coding question. Requested to do in O(n ) time complexity as oppsed to O(n2) suggested by me.
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Q1. Given an array find all the numbers whose sum is 11 using streams only
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Q2. Spring boot basics, hibernate queries, what is native query
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Q1. Design patterns in Java, write a singleton class
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Q2. Spring IOC and AOP
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Q1. How do you handle difficult stakeholders?
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Q2. Insurance policy lifecycle
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Q3. Simple Join sql query
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Q1. Difference between BA and PO
Ans. 
Business Analyst (BA) focuses on understanding business needs and requirements, while Product Owner (PO) focuses on defining and prioritizing product features.
• BA analyzes business processes and systems to identify areas for improvement, while PO works closely with stakeholders to define product features and prioritize the product backlog.

• BA typically works on multiple projects simultaneously, while PO is dedicated to a...read more
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Q2. No relevant questions in 2nd round
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