Java Back End Developer Interview Questions and Answers

Design a layered architecture for saving user data to db with appropriate annotations.

• Create a data access layer (DAO) to interact with the database using annotations like @Repository

• Implement a service layer to handle business logic with annotations like @Service

• Use @Entity annotation on model classes to map them to database tables

• Add @Id annotation on primary key fields in model classes

• Utilize @Transactional annotation on service methods for transaction management

SQL query to find nth highest salary using LIMIT and OFFSET.

• Use ORDER BY salary DESC to sort salaries in descending order.

• Use LIMIT 1 OFFSET n-1 to get the nth highest salary.

• For example, SELECT salary FROM employees ORDER BY salary DESC LIMIT 1 OFFSET 2 will give the 3rd highest salary.

LinkedHashSet is the data structure to use for storing data in order of insertion and uniqueness.

• LinkedHashSet maintains insertion order and ensures uniqueness of elements.

• It uses a combination of LinkedList and HashSet to achieve this.

• Example: LinkedHashSet set = new LinkedHashSet<>();

Using RestControllerAdvice to handle exceptions at controller level in Java

• Create a class annotated with @RestControllerAdvice to handle exceptions globally

• Use @ExceptionHandler annotation in the class to define methods to handle specific exceptions

• Return ResponseEntity with appropriate status code and error message in the exception handling methods