Introduction
If you are searching for the JPA Interview Questions, then you are in the right place because, In this article, we will discuss some of the important JPA Interview Questions that were generally asked.
JPA (Java Persistence API) is a fundamental technology for building data-driven applications in Java. As a developer looking to land your dream job, being comfortable with JPA concepts is essential. This comprehensive blog dives into the top 30+ JPA interview questions for 2024, providing insightful answers to help you impress interviewers and secure your next role.
So, without further ado, let's discuss the JPA Interview Questions.
JPA Interview Questions for Freshers
1. What is JPA?
JPA is the acronym for Java Persistent API, a Java specification used to persist data between the Java object and the relational database. It acts as the link between the object-oriented domain models and relational database systems. It requires an implementation as it doesn't perform any function itself. JPA 1.0 is the first version of the Java Persistence API released in 2006.
2. What are the advantages of JPA?
The advantages of JPA are-
- Due to O/R mapping and Database access processing, user programming becomes easy.
- The price of creating the definition file is minimized by using annotations.
- JPA will reduce the interaction with the database.
- We can also merge the applications used with other JPA providers.
3. What is the difference between the JPA and Hibernate?
The difference between the JPA and Hibernate are as follows-
- Hibernate is one of the most popular open-source implementations of the latest specification of JPA (JPA 2.1).
- JPA describes rules and APIs only but Hibernate implements these descriptions.
- JPA defines the specification, and It is an API.
4. Define Entity.
An entity is a group of states associated with a single unit, or an entity is an application-defined object in the Java Persistence Library. It behaves as an object and becomes a principal constituent of the object-oriented paradigm.
5. What are the different properties of an entity?
The properties of an entity are following-
- Persistability: If an object is stored in the database and can be accessed anytime, then that object is called persistent.
- Persistent Identity: Each Entity is unique and represents an object identity in Java. Similarly, A object is represented as a persistent identity when stored in a database. This object identity is similar to the primary key in the database.
- Transactionality: Transactions are a fundamental part of persistence, and it is a set of operations that either fail or succeed as a unit.
- Granularity: Entities should not be primitives or built-in objects with a single-dimensional state.
6. What is the role of the Entity Manager in Java Persistence API?
The following roles of the Entity Manager in JPA are-
- An entity manager is responsible for managing an object referenced by an entity.
- Entity Manager is accountable for implementing the API and encapsulating all of them within a single interface.
- It is used for operations like reading, deleting, and writing an entity.
7. What is an Entity manager?
The EntityManager is responsible for implementing an API that manages the lifecycle of entity instances. They manage a set of entities that are defined by a persistence unit.
The EntityManager API is used to create and remove persistent entity instances and find entities by their primary key, and query over entities. A persistence unit defines the set of entities that a given EntityManager instance can manage.
8. What are the basic requirements that the entity class has?
An entity class must have the following requirements:
- It must have a no-argument constructor.
- The class can't be final.
- It must be annotated with @Entity annotation.
- It must implement a Serializable interface if the value passes an empty instance as a detached object.
9. What is object-relational mapping?
Object-relational mapping is a mechanism to develop and maintain a relationship between an object and the relational database. It can do so by mapping an object state into the database column. Object-relational mapping converts attributes of programming code into columns of the table.
10. List some ORM frameworks.
The following are the various frameworks that function on the ORM mechanism: -
- Hibernate
- TopLink
- ORMLite
- iBATIS
- JPOX
11. What are the various directions of entity mapping?
The direction of mapping will be either unidirectional or bidirectional. In unidirectional mapping, we can map only one Entity to another entity. In contrast, in bidirectional mapping, we can map each Entity to another entity or refer to another entity.
12. What type of annotations are used for issuing elements of the Entity collections?
The OrderBy and OrderColumn annotations are used to establish the procedure for issuing elements of the entity collections.
13. What are the different types of entity mapping?
The different types of entity mapping are-
- One-to-one mapping: In this mapping, an instance of one Entity is associated with an instance of another entity that represents a single-valued association.
- One-To-Many mapping: In this mapping, an entity is associated with a collection of other entities that come into the collection-valued association category.
- Many-to-one mapping: A collection of entities can be associated with a similar entity in this mapping.
- Many-to-many mapping: This mapping is a collection-valued association where any number of entities can be associated with a collection of other entities.
14. What are the different types of objects that can be stored in the JPA collections mapping?
The different types of objects that JPA allows to store are-
- Basic Types
- Entities
- Embeddable
15. What is JPQL?
JPQL, an acronym for Java Persistence Query language (JPQL), is a part of the JPA specification that defines searches against persistence entities. It is an object-oriented query language that performs database operations on persistent entities. JPQL uses an entity object model instead of the database to operate the SQL queries. Here, the primary role of JPA is to transform JPQL into SQL. Hence, it provides an easy platform for developers to handle SQL tasks.
16. What are the essential features of JPQL?
The essential features of JPQL are-
- JPQL is simple and robust.
- JPQL is a platform-independent query language.
- The queries of JPQL can be declared statically into metadata or dynamically built-in code.
- JPQL can be used with any database such as MySQL or Oracle.
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