Top questions with answers asked in MNC on Advance Java Hibernate

Advanced Java Hibernate interview questions along with their answers:

1. What is Hibernate, and how does it differ from JDBC?
   • Answer: Hibernate is an open-source Object-Relational Mapping (ORM) framework for Java that simplifies database interactions by mapping Java objects to database tables. It provides a higher level of abstraction and eliminates the need for manual SQL queries and result set processing, making database access more efficient and developer-friendly. Unlike JDBC, which requires developers to write SQL queries and handle database connections manually, Hibernate automates many database-related tasks and provides an object-oriented interface for data persistence.
2. What are the main advantages of using Hibernate ORM?
   • Answer: The main advantages of using Hibernate ORM include:
     • Simplified Database Interactions: Hibernate eliminates the need for manual SQL queries and result set processing by providing an object-oriented interface for database operations.
     • Automatic Mapping: Hibernate automatically maps Java objects to database tables and handles the conversion of data types, reducing the need for manual mapping and configuration.
     • Transparent Persistence: Hibernate manages the lifecycle of persistent objects and automatically synchronizes changes between Java objects and the database, making data persistence transparent to the developer.
     • Caching and Performance Optimization: Hibernate provides caching mechanisms to improve performance by caching frequently accessed data and reducing database round-trips.
     • Transaction Management: Hibernate supports declarative transaction management, allowing developers to define transaction boundaries and rollback behavior using annotations or XML configuration.
3. What is the difference between save() and persist() methods in Hibernate?
   • Answer:
     • save(): The save() method in Hibernate is used to persist an entity (i.e., save it to the database) and return its generated identifier (primary key value). If the entity is transient (i.e., not associated with any session), save() assigns a new identifier to the entity and inserts it into the database.
     • persist(): The persist() method is similar to save() but is intended for use within a transaction context. It makes a transient entity persistent and assigns an identifier to it, but it does not guarantee immediate execution of the SQL INSERT statement. The persistence context is synchronized with the database during the flush operation or at the end of the transaction.
4. What is Hibernate HQL (Hibernate Query Language), and how does it differ from SQL?
   • Answer: Hibernate Query Language (HQL) is a query language provided by Hibernate for performing database operations on persistent objects. HQL is similar to SQL but operates at the object level, allowing developers to write queries using entity names and properties rather than table names and columns. Unlike SQL, which operates on database tables directly, HQL operates on mapped entity classes and their properties, providing a higher level of abstraction and platform independence.
5. What is lazy loading in Hibernate, and how does it improve performance?
   • Answer: Lazy loading is a feature provided by Hibernate for fetching associated entities or collections lazily, i.e., on-demand when they are accessed for the first time. In lazy loading, associated entities are not loaded along with the parent entity but are fetched from the database only when they are explicitly accessed through getter methods. Lazy loading improves performance by reducing the amount of data loaded into memory and minimizing database queries, especially for large and complex object graphs. However, lazy loading should be used judiciously to avoid performance issues like the N+1 query problem.