20 Java ORM Interview Questions and Answers

Java ORM is a programming language that helps developers map data from a database to an object-oriented program. If you’re applying for a position that involves Java ORM, you can expect to be asked questions about your experience and knowledge during the interview process. In this article, we review some of the most common Java ORM questions and provide tips on how to answer them.

Java ORM Interview Questions and Answers

Here are 20 commonly asked Java ORM interview questions and answers to prepare you for your interview:

1. What is Object-Relational Mapping (ORM)?

ORM is a technique for mapping data between objects and relational databases. It allows developers to work with objects while the ORM layer handles translating those objects into SQL queries that are executed against the database. This can make working with databases much simpler and more efficient, as developers don’t have to write SQL queries by hand.

2. Can you explain the difference between ORM and JDBC?

ORM (Object Relational Mapping) is a technique that allows you to map objects in your programming language to database tables. This means that you can work with objects in your code, and the ORM layer will take care of translating those objects into the appropriate SQL queries to manipulate the data in the database. JDBC (Java Database Connectivity) is a Java API that allows you to directly execute SQL queries on a database. With JDBC, you are responsible for writing the SQL queries as well as any code to map the results of those queries back to objects in your code.

3. Why do we need an ORM tool in Java?

ORM stands for Object Relational Mapping. It is a technique that allows us to map data from a relational database into objects that we can use in our Java code. This is useful because it allows us to work with the data in a more natural way, and it also reduces the amount of code that we have to write.

4. Which Java API can be used to map objects to relational databases?

The Java Persistence API (JPA) is a Java API that can be used to map objects to relational databases.

5. What are some advantages of using ORM over JDBC?

ORM provides a number of advantages over JDBC, including the ability to more easily map objects to database tables, support for lazy loading of data, and improved performance through caching. Additionally, ORM can make it easier to work with complex data structures, and can provide a higher level of abstraction, making code more maintainable.

6. Is it possible to use ORM without XML configuration? If yes, then how?

Yes, it is possible to use ORM without XML configuration. This can be done by using annotations instead of XML to configure the ORM.

7. What’s the difference between JPA and Hibernate?

JPA is a specification for ORM in Java, while Hibernate is a specific implementation of that specification. JPA defines the standard for how Java objects should be mapped to database tables, and Hibernate provides a specific implementation of that standard.

8. How would you configure a Spring application to use Hibernate as its ORM framework?

You would need to add the hibernate-core and hibernate-entitymanager dependencies to your project, and then configure the SessionFactory bean in your Spring application context.

9. What are the different types of associations that can exist between two entities?

The different types of associations that can exist between two entities are:

One-to-one: This is a relationship where each entity is associated with only one other entity.

One-to-many: This is a relationship where one entity is associated with multiple other entities.

Many-to-one: This is a relationship where multiple entities are associated with only one other entity.

Many-to-many: This is a relationship where multiple entities are associated with multiple other entities.

10. What are the different ways of persisting data in Hibernate?

Hibernate supports four different ways of persisting data:

1. Transient: This is the default state of an object when it is first created. It is not associated with a Hibernate Session and is not persisted to the database.

2. Persistent: A persistent object is associated with a Hibernate Session and is persisted to the database.

3. Detached: A detached object is no longer associated with a Hibernate Session but is still persisted to the database.

4. Removed: A removed object is associated with a Hibernate Session but is not persisted to the database.

11. What does the SessionFactory interface do in Hibernate?

The SessionFactory interface is the main entry point into Hibernate. It is used to create Session objects, which are used to perform persistence operations.

12. What are the important annotations provided by Hibernate for mapping properties of an entity class with columns in a database table?

The most important annotations provided by Hibernate for mapping properties of an entity class with columns in a database table are @Column and @Id. The @Column annotation is used to map a property of an entity class to a column in a database table, while the @Id annotation is used to map a property of an entity class to the primary key column of a database table.

13. What are some useful features offered by Hibernate?

Hibernate is a Java ORM tool that offers a number of features that can be useful for developers. These features include automatic table creation, support for multiple databases, and the ability to generate SQL queries. Hibernate also offers a number of other features that can be useful for developers, such as caching and lazy loading.

14. Can you name some of the most popular ORM tools available for Java applications?

Some of the most popular ORM tools available for Java applications include Hibernate, iBatis, and Java Persistence API (JPA).

15. What are the main differences between Hibernate and MyBatis?

The main difference between Hibernate and MyBatis is that Hibernate is a full-fledged ORM solution while MyBatis is a SQL mapping tool. Hibernate provides a complete framework for mapping an object-oriented domain model to a relational database. MyBatis, on the other hand, is a simpler tool that only performs object-relational mapping.

16. What are the benefits of using MyBatis?

MyBatis is a lightweight, yet powerful, Java ORM tool that enables developers to quickly and easily map Java objects to database records. MyBatis is fast, efficient, and easy to use, making it a great choice for Java developers looking for an ORM solution.

17. What are the most common problems associated with ORM frameworks like Hibernate or MyBatis?

The most common problems with ORM frameworks are related to performance. Because ORM frameworks need to map objects to database tables, they can introduce a lot of overhead which can impact the performance of an application. Additionally, ORM frameworks can be complex to configure and use, which can lead to developer errors that can impact the stability of an application.

18. What is lazy loading?

Lazy loading is a technique for loading data on demand. With lazy loading, data is not loaded until it is needed. This can improve performance by reducing the amount of data that needs to be loaded and processed.

19. What is eager fetching?

Eager fetching is the process of loading all of the data for a particular relationship in advance, typically when the parent object is first loaded. This can be useful if you know that you will need to access the data in the relationship frequently, but it can also lead to performance issues if the data is not actually used very often.

20. What is named query?

A named query is a query that is given a name so that it can be easily referenced later. This is useful if you want to reuse the same query multiple times or if you want to make sure that the query is consistent across different parts of your code.