If you’re at a job interview, the last thing you want is to get stumped on a question. It’s especially frustrating if you’re well-versed on the subject in question, but you could have benefitted from a refresher beforehand.

That’s why it’s a sound strategy to review some old material and brush up on the more common interview questions. This way, you won’t get caught off-guard and possibly tarnish that crucial first impression.

If you’re applying for a Hibernate-related position, then you’ve come to the right place. Here are two dozen of the most popular interview questions, broken down by difficulty level. You will find entry-level information, intermediate concepts, and Hibernate interview questions for experienced applicants.

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Let’s start off with the Hibernate interview questions by taking a brief look at Hibernate.

What is Hibernate, and Why Should We Care?

Hibernate ORM, also known as just “Hibernate,” is a lightweight, open-source object-relational mapping tool used in the Java programming language, providing a framework that maps object-oriented domain models to relational databases.

Hibernate makes it easier to create objects independent of database software and develop persistence logic. Put in simple, non-technical terms, Hibernate is a free tool that facilitates interactions between your application and the database.

You can find out more about Hibernate and other popular Java applications here.

Let us now begin with the basic or the entry-level Hibernate interview questions and answers.

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Basic Level Hibernate Interview Questions

Let’s start with the fundamentals in these hibernate interview questions. These first eight Hibernate-related questions cover simple, entry-level basics.

1. What is an ORM tool?

A:  An Object Relational Mapping (ORM) tool helps to simplify data creation, manipulation, and access by internally using Java API to interact with the databases. It’s a technique that maps objects stored in a database.

2. What does “lightweight” mean?

A: In the context of computers, “lightweight” describes an app, computer program, or device that doesn’t use many system resources due to its small memory footprint (RAM) and low CPU usage.

3. What are the advantages of Hibernate?

A: Here’s a list of Hibernate’s many advantages:

  • It’s fast
  • It’s lightweight and open source
  • It reduces code length, removing boilerplate code, freeing up developers for other tasks
  • It strengthens the object-level relationship
  • It facilitates the generation of independent database queries
  • It provides resources for creating tables automatically
  • It’s easy to integrate with other Java Enterprise Edition (EE) frameworks.

4. Why is Hibernate better than Java Database Connectivity (JDBC)?

A: Hibernate outclasses JDBC because:

  • Hibernate code is cleaner and more readable thanks to the elimination of boiler-plate code, something found in JDBC
  • Unlike JDBC API, Hibernate supports associations, collections, and inheritances
  • HQL (Hibernate Query Language) is closer to Java and is more object-oriented
  • Developers don’t need to write code to store and load data into the database
  • Hibernate enables faster application development

5. What is “persistence”?

A: In the context of Java, persistence describes data and objects that last beyond the process used to create them.

6. Name some databases that Hibernate supports.

A: Hibernate supports databases like:

  • DB2/NT
  • FrontBase
  • HSQL Database Engine
  • Informix Dynamic Server
  • Microsoft SQL Server Database
  • MySQL
  • Oracle
  • PostgreSQL
  • SQL Server
  • Sybase

7. What is HQL?

A: HQL stands for Hibernate Query Language, a powerful object-oriented language independent of the database. It’s like SQL, except that it uses objects instead of table names. HQL is a very simple, efficient, and flexible query language used to do various operations on a relational database without the need for complex database queries.

8. Name the four ORM levels in Hibernate.

A: Hibernate’s four ORM levels are:

  • Full Object Mapping
  • Light Object Mapping
  • Medium Object Mapping
  • Pure Relational

After looking into some of the basic Hibernate interview questions, let us level up and look into the intermediate level questions.

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Intermediate Level Hibernate Interview Questions

Let’s push the difficulty level up a few notches with this set of eight moderately challenging Hibernate interview questions and answers.

9. Name Hibernate’s five collection types used in one-to-many relationship mappings.

A: The five collection types are:

  • Array
  • Bag
  • List
  • Map
  • Set

10. What is “dirty checking”?

A: The dirty checking feature helps developers and users avoid time-consuming write actions, thereby reducing database write times. Dirty checking changes or updates only the fields that require action, while keeping the rest of the fields untouched and unchanged.

11. What is Hibernate’s default cache service?

A: Hibernate’s default cache service is EHCache, though the framework additionally supports OSCache, SWARMCache, and TreeCache.

12. What is Light Object Mapping?

A: Light Object Mapping is one of the more valuable levels of ORM quality. This approach uses specific design patterns to hide the syntax from business logic. All entities are represented as classes and mapped manually. The Light Object Mapping approach works well with applications that have fewer entities and applications that use metadata-driven data models.

13. List and describe the Hibernate framework’s essential interfaces.

A: Hibernate’s important interfaces are:

  • SessionFactory (org.hibernate.SessionFactory). SessionFactory is an immutable thread-safe cache of compiled mappings meant for a single database. After users initialize SessionFactory once, they can cache and reuse it. SessionFactory is designed to return the session objects for database operations.
  • Session (org.hibernate.Session). A session is a single-threaded, short-lived object that represents a dialogue between the persistent store and the application. It is the interface that exists between the Hibernate framework and the Java application code, providing methods for CRUD operations. A session should be opened only when required, then closed as soon as the user is finished.
  • Transaction (org.hibernate.transaction). The transaction is a single-threaded, short-lived object that the application uses to specify atomic units of work.

14. What is lazy loading?

A: Lazy loading is a technique where objects are loaded as needed, instead of an entire page, for example. This technique became default since Hibernate version 3.

15. What are the concurrency strategies?

A: Concurrency strategies are mediators responsible for storing and retrieving cached items. When enabling a second-level cache, the developer must decide which cache concurrency to implement for each persistent class and collection.

The concurrency strategies are:

  • Non-strict-Read-Write: This strategy works with data that can be altered and can tolerate a small chance of stale data. This strategy offers no guarantee of consistency between the database and the cache.
  • Read-Only: This strategy works best with data that can’t be changed, and consequently, is only used to reference data.
  • Transactional: This strategy is used primarily for read-mostly data in cases where it’s essential to prevent stale data in concurrent transactions, in those rare instances of an update.
  • Read-Write: This strategy is like the transactional strategy.

16. Define Hibernate’s validator framework.

A: Data validation is an integral part of any application and is used in the presentation layer when using JavaScript and server-side code before processing. Validation is a cross-cutting task that occurs before making it persistent so that it adheres to the correct format.

Now that we have learned some of the intermediate level Hibernate interview questions, let us next increase the difficulty level and look into some of the advanced level Hibernate interview questions and answers.

Advanced Level Hibernate Interview Questions

We round out the Hibernate interview questions with eight expert questions.

17. What design patterns does the Hibernate framework use?

A: Some design patterns include:

  • Data Mapper, which moves data between objects and a database, keeping them independent of each other and the mapper
  • Domain Model Pattern, which is a domain object model that incorporates both behavior and data
  • Proxy Pattern, for lazy loading
  • Factory pattern in SessionFactory

18. What is Hibernate tuning?

A: The process of Hibernate tuning is designed to optimize Hibernate applications’ performance. The three strategies are:

  • SQL Optimization
  • Session Management
  • Data Caching

19. Name the states that a persistent entity exists in.

A: Persistent entities exist in only three states:

  • Transient
  • Persistent
  • Detached

20. How can you view the Hibernate-generated SQL on a console?

A: To enable viewing SQL on a console for debugging purposes, you must add the following in the Hibernate configuration file:

1 <property name="show_sql">true</property>

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21. What’s the difference between Session and SessionFactory?

A: A Session provides the first-level cache and is a single-threaded, short-lived object. A SessionFactory provides the second-level cache and is immutable and shared by all Sessions. It lives until Hibernate is running.

22. How many ways can an object be fetched from Hibernate’s database?

A: There are four ways to fetch objects from Hibernate’s database:

  • Criteria API
  • HQL
  • The identifier
  • Standard SQL

23. How many ways can you disable Hibernate’s second-level cache?

A: There are three ways to disable the cache:

  • By setting hibernate. cache. use_second_level_cache property to false
  • Using a cache provider such as org.hibernate.cache.NoCacheProvider

24. Describe the differences between Hibernate’s transient, persistent, and detached states.

A: Here is how the states differ:

  • Transient. This state describes new objects that are created in Java but not associated with a Hibernate session.
  • Persistent. This state describes objects associated with a Hibernate session.
  • Detached. This state describes an object that was formerly Persistent and associated with a Hibernate session. Developers can reattach the object to a Hibernate session by using either update() or saveOrUpdate().

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