Explain what is pdv

Difference between == and equals() How does HashMap work internally? Difference between HashMap and ConcurrentHashMap What is immutable class? How to create one? Explain OOP concepts with real examples What are checked vs unchecked exceptions? Difference between ArrayList and LinkedList How does Garbage Collection work in Java? What is String pool? SQL Queries Questions Find the second highest salary from a table Difference between INNER JOIN and LEFT JOIN What is index? When should we use it? Difference between WHERE and HAVING How to remove duplicate records from a table? Explain normalization What are primary key and foreign key? Spring / Spring Boot Questions Difference between Spring Framework and Spring Boot What is Microservices architecture? Difference between Monolith and Microservices How do microservices communicate with each other? What is service discovery? How do you handle failure in microservices? What is API Gateway? Basics of Kafka / async communication What is dependency injection? Explain @Component, @Service, @Repository What is @Autowired and how it works? Difference between @Controller and @RestController What is Spring Boot auto-configuration?