Top 20 Java JPA Interview Questions and Answers

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JPA stands for Java Persistence API. It was introduced by Sun Microsystems as part of the EJB 3.0 specification and later became a standard under Oracle. JPA helps developers manage relational data in Java applications by simplifying database operations. It is widely used in backend development, enterprise apps, and data-driven platforms. Many roles like Java Developer, Backend Engineer, and Full Stack Developer require a strong grip on JPA. In this guide, we have covered the 20 most asked Java JPA interview questions with simple answers to help you prepare.

Fun Fact: Even though JPA is part of Java, it doesn’t work on its own. You always need a provider like Hibernate to actually make it work behind the scenes.

JPA Interview Questions for Freshers 

Here are some basic-level Java JPA interview questions that are commonly asked to freshers and entry-level professionals. 

1. What is JPA and how does it differ from JDBC?

JPA (Java Persistence API) is a standard in Java for mapping objects to relational database tables. It allows managing data through entities instead of writing raw SQL.

Here are the key differences: 

• JPA works with objects; JDBC works with SQL queries.
• JPA handles entity states and relationships automatically.
• JDBC requires manual connection, query execution, and result processing.

2. What is the role of the @Entity annotation?

The @Entity annotation tells JPA that a class represents a table in the database. Without it, JPA won’t recognize the class as something it should manage or store.

3. What is the difference between JPQL and SQL?

JPQL works with Java objects, while SQL works with database tables. JPQL uses entity names, not table names, and returns Java entities. It is converted to SQL internally by the JPA provider.

4. How do you define a primary key in a JPA entity?

You use the @Id annotation on a field to mark it as the primary key. This key uniquely identifies each record in the table mapped to that entity.

5. What is the function of the @GeneratedValue annotation?

@GeneratedValue automatically generates a value for the primary key. It is useful when I don’t want to manually assign IDs for each new record. It supports strategies like AUTO, IDENTITY, and SEQUENCE.

6. What is the purpose of the EntityManager in JPA?

EntityManager is the main interface for working with JPA. It lets me perform actions like insert, update, delete, and query entities. It manages the persistence context and tracks changes to objects.

Also Read - Top 20 JDBC Interview Questions and Answers

JPA Interview Questions for Experienced 

Let’s go through some advanced JPA interview questions and answers for experienced professionals who are aiming for senior-level Java roles.

7. What are the main differences between persist(), merge(), and save()?

persist() is used to add a new entity to the persistence context. It works only with new (transient) objects. 

merge() is for detached entities – those not currently managed. It copies their state to a managed instance. 

save() is not part of JPA but comes from Spring Data JPA and can handle both new and detached entities.

8. How does JPA handle optimistic locking with @Version?

JPA uses the @Version annotation to track changes to an entity. When I update a record, the version is checked. If someone else updated it first, JPA throws an OptimisticLockException. This avoids overwriting changes silently.

9. What is a persistence context, and how does it impact performance?

The persistence context is a set of managed entities tracked by the EntityManager. It acts like a first-level cache. If I query the same entity twice in one transaction, JPA serves it from memory. This reduces database hits and speeds up read operations. But keeping too many entities managed can increase memory use.

10. How does lazy vs eager fetching affect query performance?

Lazy fetching loads related entities only when accessed. It reduces the initial query size. Eager fetching loads everything at once, even if I don’t need it yet. Lazy is better for large data sets. Eager can be faster when I know I will use all related data immediately.

11. What is a named query and when would you use one?

A named query is a pre-defined JPQL query declared using @NamedQuery. It is defined in the entity class and reused by name. I use it for common queries that don’t change. It is cleaner and faster since the query is parsed at startup.

12. What are the pros and cons of using a second-level cache in JPA?

The second-level cache stores entities across sessions. It can improve performance by avoiding repeated database reads. But it can cause stale data if not configured properly. I use it only when the data changes infrequently.

Spring Data JPA Interview Questions

Here are some commonly asked Spring Data JPA interview questions to test your understanding of repositories, query methods, and data access patterns.

13. What is the difference between CrudRepository and JpaRepository?

CrudRepository provides basic CRUD methods like save(), findById(), and delete(). JpaRepository extends it with more features like flush(), batch delete, and pagination support. I usually prefer JpaRepository for complex projects.

14. How do derived query methods work in Spring Data JPA?

Derived queries are built by method names. I just write a method like findByEmail (String email) and Spring builds the query for it. It reads the method name, matches it with entity fields, and creates the query behind the scenes.

15. What is the purpose of the @Query annotation in Spring Data JPA?

@Query is used when the query is too complex for a method name. I can write JPQL or native SQL inside it. It is useful for joins, custom conditions, or projections.

16. How does Spring Data JPA support pagination and sorting?

Pagination is handled using Pageable, and sorting uses Sort. I pass them as parameters in repository methods. For example, findAll(Pageable pageable) returns one page of sorted data instead of loading everything. This improves performance in large datasets.

Note: We have also included Spring Data JPA interview questions for experienced professionals, including those with 5 years and 10 years of experience.

Also Read - Top 25+ Spring Framework Interview Questions and Answers

Spring Data JPA Interview Questions for 5 Years Experienced

• How do you create custom repository methods in Spring Data JPA?
• What is the difference between save() and saveAndFlush()?
• How do you handle transactions in Spring Data JPA?
• How do you manage performance in Spring Data JPA when fetching large datasets?

Spring Data JPA Interview Questions for 10 Years Experienced

• How would you design a scalable Spring Data JPA architecture in a microservices environment?
• How do you integrate Spring Data JPA with QueryDSL or Specifications?
• How do you tune performance for complex joins and nested queries in Spring Data JPA?
• How do you manage version conflicts in concurrent transactions using Spring Data JPA?

Hibernate JPA Interview Questions

Here are important Hibernate JPA interview questions to help you understand how Hibernate works as a JPA implementation.

17. How is Hibernate related to JPA?

Hibernate is one of the most widely used implementations of the JPA specification. JPA defines the rules, and Hibernate follows them while adding extra features. I often use Hibernate as the JPA provider in Spring Boot projects.

18. What is implicit polymorphism in Hibernate?

Implicit polymorphism means a query on a superclass can return objects of its subclasses too. Hibernate includes all subclasses in a query result unless I tell it not to. This makes it easier to work with inheritance.

19. What are the different inheritance mapping strategies in Hibernate?

Hibernate supports three strategies: SINGLE_TABLE, TABLE_PER_CLASS, and JOINED. 

SINGLE_TABLE stores all classes in one table. 

JOINED keeps parent and child data in separate tables and joins them.

TABLE_PER_CLASS makes one table for each class in the hierarchy.

20. How does Hibernate implement first-level and second-level caching?

First-level cache is built into the Session object. It stores entities within a transaction. Second-level cache stores data across sessions. I can enable it using providers like Ehcache or Infinispan. It helps reduce database hits when the same data is requested again.

Also Read - Top 60+ Hibernate Interview Questions and Answers

Tips to Prepare for JPA Interview

Preparing for a JPA interview can be tricky if you are not clear on the core concepts. So, make sure you follow these tips:

• Focus on entity mapping and lifecycle states
• Practice writing JPQL and Criteria queries
• Understand how EntityManager works
• Study fetch types and caching
• Review common Java JPA interview questions and build small projects to apply concepts in real code

Wrapping Up

With these 20 Java JPA interview questions and answers, you are better prepared to face real interviews. Keep practicing, build small projects, and stay confident with your JPA concepts. 

If you are looking for JPA job roles, visit Hirist – a top platform to find IT jobs, including openings for Java and JPA professionals.

FAQs

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Experience range in data	1 – 4 years