Persistent Systems Java Developer Interview Questions, Process, and Tips

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
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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
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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
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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
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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. Given an input string s ="aabbbcddbb". Write a java program to get output as a2b3c1d2b2
Ans. 
Java program to count consecutive characters in a string
• Iterate through the input string and compare each character with the next one

• Use a StringBuilder to build the output string with character and count

• Handle edge cases like empty string or single character input
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Q2. Find 3rd highest from a list using streams api.
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Use streams api to find 3rd highest number from a list.
• Convert the list to a stream using list.stream()

• Sort the stream in descending order using sorted(Comparator.reverseOrder())

• Skip the first two elements using skip(2) and get the third element using findFirst().get()
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Q1. Write a Rest api to get employee details by employee id.
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A Rest api to get employee details by employee id
• Create a GET endpoint with a path like '/employees/{employeeId}'

• Retrieve employee details from a database using the employee id

• Return the employee details in JSON format
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Q2. Exceptional handling?
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Q1. What is Custom exception?
Ans. 
Custom exception is a user-defined exception that extends the functionality of the built-in exceptions in Java.
• Custom exceptions are created by extending the Exception class or one of its subclasses.

• They allow developers to define their own exception types for specific scenarios.

• Custom exceptions can include additional methods and fields to provide more information about the exception.

• Example: public class CustomExcept...read more
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Q2. What is roles and responsibilities in your project?
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Q3. Find out duplicate element in array?
Ans. 
Use a HashSet to find duplicate elements in an array of strings.
• Create a HashSet to store unique elements.

• Iterate through the array and check if the element is already in the HashSet.

• If it is, then it is a duplicate element.

• Example: String[] array = {"apple", "banana", "apple", "orange"};
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Q1. Java 8 features
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Q2. What is functional programming
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Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing state and mutable data.
• Focuses on pure functions that do not have side effects

• Emphasizes immutability and avoids changing state

• Supports higher-order functions and function composition

• Examples include languages like Haskell, Scala, and Clojure
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