CitiusTech Junior Java Developer Interview Questions and Answers

Q1. Static related que sql query to fetch data starting with vowel method overriding exceptions
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Q1. Given an array of non-negative integers.Find the length of the longest subsequence such that elements in the subsequence are contiguous integers. The consecutive numbers can be in any order. Example n=7 nu...read more
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Find the length of the longest subsequence of contiguous integers in an array.
• Sort the array

• Iterate through the array and check for consecutive integers

• Keep track of the longest subsequence found
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Q2. Get list of pincodes from these objects Employee{ id Long, name String, Addresses : List
} Addresses{ houseNo long, pindcode long, state String, country String, } Ans. Use flatMap to flatten and then use m...read more
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Use flatMap and map to extract list of pincodes from Employee objects
• Use flatMap to flatten the list of Addresses in each Employee object

• Use map to iterate over the flattened list and extract the pincodes

• Example: employeeList.stream().flatMap(emp -> emp.getAddresses().stream()).map(address -> address.getPincode()).collect(Collectors.toList())
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Q3. What is Database Pooling, Hikari and its configurations. Java 8 to current enchancements and current java version Factory and Builder design patterns to explain and code Project expalantion and details, Cr...read more
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Database pooling is a technique used to manage a pool of database connections for efficient resource utilization. HikariCP is a popular database connection pooling library in Java.
• HikariCP is a high-performance database connection pooling library for Java applications.

• It is known for its low latency and high throughput.

• Configurations for HikariCP include settings such as maximum pool size, connection timeout, and idle ...read more
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Q1. How annotation works?
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Annotations in Java provide metadata about a program that can be used by the compiler or at runtime.
• Annotations start with the @ symbol.

• Annotations can be used to provide information to the compiler or to runtime environments.

• Annotations can be used to define custom metadata for classes, methods, fields, etc.

• Annotations can also be used for code generation, documentation, and validation.

• Examples of annotations in Java ...read more
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Q2. CondurentSkipListMap, how does it work
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ConcurrentSkipListMap is a concurrent, sorted map implementation in Java.
• ConcurrentSkipListMap is a concurrent version of SkipListMap, which is a sorted map implementation based on skip list data structure.

• It allows multiple threads to access and modify the map concurrently.

• It provides logarithmic time complexity for most operations, making it efficient for concurrent access.

• Example: ConcurrentSkipListMap
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1 Assignment which you need to solve in front of the interviewer

Q1. Questions on Java Streams
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Q2. Questions on springboot
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Q1. To connect to your DB what you use in Spring boot
Ans. 
In Spring Boot, we use Spring Data JPA to connect to the database.
• Use @EnableJpaRepositories annotation in the main application class to enable JPA repositories

• Define datasource properties in application.properties or application.yml file

• Use @Entity annotation to define JPA entities

• Use JpaRepository interface to perform CRUD operations on entities
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Q2. What is Component Scan
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Component Scan is a feature in Spring framework that automatically scans and registers Spring components in the application context.
• Component Scan is used to automatically detect and register Spring components like @Component, @Service, @Repository, and @Controller.

• It eliminates the need for manual configuration of bean definitions in the Spring configuration file.

• Component Scan can be configured with base package(s) t...read more
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Q3. Throw vs throws
Ans. 
throw is used to explicitly throw an exception in a method, while throws is used in method signature to declare the exceptions that can be thrown by the method.
• throw is used within a method to throw an exception, while throws is used in the method signature to declare the exceptions that can be thrown by the method

• throw is followed by an exception object, while throws is followed by the exception class names separated ...read more
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Q1. Java vs Javascript , Meaning of Synchronization in Java , Multihreading in Js
Ans. 
Java is a backend language, Javascript is a frontend language. Synchronization in Java ensures only one thread can access a resource at a time. JavaScript is single-threaded but can handle asynchronous operations using callbacks, promises, and async/await.
• Java is a backend language used for server-side development, while JavaScript is a frontend language used for client-side scripting.

• Synchronization in Java is a techn...read more
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Q2. Write a pojo class to display the Employee Details,Pojo vs Bean
Ans. 
A Pojo class is a simple Java class that contains only private fields, public getters and setters, and no-arg constructor.
• Create private fields for employee details like name, id, salary, etc.

• Generate public getters and setters for each field.

• Include a no-arg constructor in the class.

• Example: public class Employee { private String name; private int id; public String getName() { return name; } public void setName(String...read more
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Q3. How to to compare two objects with same class (equals & Hashcode methods)
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To compare two objects with the same class, override the equals and hashCode methods in the class.
• Override the equals method to compare the fields of the objects for equality.

• Override the hashCode method to generate a unique hash code based on the object's fields.

• Ensure that the equals and hashCode methods are consistent with each other.

• Example: public class Person { private String name; private int age; }
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Q4. Springboot questions basics like How to connect to 2 databases at a time How to change the table name in entity class(@Table)
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Q5. JPA Repository inbuilt methods
Ans. 
JPA Repository provides inbuilt methods for common database operations in Spring applications.
• JPA Repository provides methods like save(), findById(), findAll(), deleteById(), etc.

• These methods help in performing CRUD operations on entities without writing custom queries.

• For example, userRepository.save(user) saves a user entity to the database.
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Q1. Java8 coding to filter the vowels
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Using Java8 to filter vowels from an array of strings
• Use Java8 stream and filter to iterate through each string in the array

• Use a lambda expression to check if each character is a vowel

• Collect the filtered strings into a new array
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Q2. Java8, Multi Threading, Hibernate, JPA
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