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Hibernate Interview Questions

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Introduction

Hibernate is a Java framework built on JPA- Java persistence API. It connects a Java application with its database very simply and efficiently. It can support various relational databases, data retrievals using queries, and an extensive range of data manipulation operations, like create, insert, update, delete, etc.   

hibernate interview questions

This blog will dive into the top 30 Hibernate Interview Questions and Answers.

For better understanding, they are classified into three sub-categories according to their difficulty level :

  • Beginner level
  • Intermediate level
  • Advanced level

Beginner-Level Hibernate Interview Questions

Here we commence the Beginner Level Hibernate Interview Questions.

Q1. What is Hibernate, and why is it used in Java development?

Hibernate is a Java framework mainly used to make the interaction between a Java application and its associated database easier and simpler to implement. It is an open-source object-relational mapping tool (ORM) that provides fast performance due to features like lightweight, HQL (hibernate query language ), automatic table creation, multiple table handling techniques, etc.

Q2. What is a session in hibernate?

A session is an intermediate link between the Java applications and their associated database. It consists of an API to perform creation and manipulation operations like read, insert, delete, update, create, etc., on the database.

Q3. What is the role of Hibernate Query Language?

The Hibernate Query Language(HQL) is a strong, object-oriented based query language used along with Hibernate Framework. It is very similar to SQL, except that we have objects instead of tables in HQL. Once implemented, the HQL queries are converted to SQL queries only.

Q4. What is the difference between transient and persistent objects in hibernate?

Transient and persistent are like the two states of an object in Hibernate. A transient state means that the current thing has not yet been saved in the database, whereas persistent means it has already been saved. If a persistent object is modified, the changes are automatically synchronised with the database during a transaction. It ensures that the changes persist and can be retrieved later.

Q5. What is the difference between the Hibernate save() and persist() methods?

When we call persist on any existing object, it transitions from transient to persistent state. However, it is not saved in the database.

When we call the save method, the existing object is immediately saved in the database and returned.

Q6. What is lazy Loading in hibernate?

Lazy loading is a technique that defers the loading of related data until it's required. When an entity is fetched from the database, only the necessary data is loaded when the application accesses it. This can improve performance when working with large datasets or when there's much data to access.

Q7. What is hibernate caching?

Hibernate caching is similar to our typical cache in our Personal Computers. It creates a temporary memory between the java application and our database, which is responsible for holding the frequently retrieved data from the database.

Q8. Explain Hibernate architecture

The following are some of the key components of the Hibernate framework:-

  • Application Layer: This is the top layer of your application where you interact with Hibernate to perform database operations.
     
  • Hibernate Configuration: Hibernate needs configuration details in XML format to connect to the database and perform various settings.
     
  • SessionFactory: The SessionFactory is a thread-safe object that is responsible for creating and managing Session instances.
     
  • Session: A Session is a short-lived, lightweight object that represents a single unit of work with the database.

Q9. What are the advantages of Hibernate over JDBC?

The main shortcoming of Java Database Connectivity(JDBC) is that its codes need to be more portable. It is dependent upon the integrated software along with our database. The case is not the same with Hibernate, as it uses objects capable of platform-independent implementation. 

Q10. What are some basic categories of mapping in hibernate?

The basic hibernate mappings categories include-

  •  Primitive types
     
  •  Date and Time types
     
  •  Binary and Large Object types
     
  •  JDK types. 
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Intermediate-Level Hibernate Interview Questions 

Here we begin the Intermediate Level Hibernate Interview Questions.

Q11:What is the purpose of a Hibernate Session, and how is it obtained?

The purpose of a Hibernate Session is to provide a single-threaded, short-lived object representing a unit of work for ORM operations. It provides methods to interact with the database to insert, update, delete, or retrieve objects. 

Q12: What is the difference between a Hibernate Session and a Hibernate SessionFactory?

A Hibernate SessionFactory is a thread-safe object used to create Hibernate Session instances. It is an expensive object, typically made only once during the application's lifetime. A Hibernate Session represents a unit of work and provides a connection to the database. In contrast, a SessionFactory represents the entire configuration of Hibernate, including the mappings between Java objects and database tables.

Q13: What are the different types of Hibernate mapping, and how are they used?

There are three types of Hibernate mappings;

  • XML mapping: It involves defining the mappings between Java objects and database tables.
     
  • Annotations mapping: It consists in determining the mappings using Java annotations. :
     
  • Mixed mapping: It allows developers to use a combination of XML configuration files and Java annotations 

Q14: How does Hibernate implement object-relational mapping (ORM)?

Hibernate implements object-relational mapping (ORM) by providing a framework for mapping Java objects to database tables. It offers a set of classes and APIs that allow Java developers to define the mappings between Java objects and database tables. 

Q15: What is the difference between HQL and SQL, and when would you use one over the other?

HQL (Hibernate Query Language) is a query language that allows developers to write queries in terms of Java objects. SQL is a query language that operates on database tables directly. HQL is a more object-oriented approach to querying data, while SQL is a more standardised approach. HQL provides greater flexibility for complex data queries, while SQL provides robust commands for working with relational databases. The choice between HQL and SQL will depend on the application's specific needs.

Q16: What is the purpose of a Hibernate Criteria API?

The Hibernate Criteria API provides an easy and programmatic way to build queries in Hibernate. It allows developers to create queries using a smooth interface and includes security, which can help prevent errors at compile time. 

Q17: How do you create an immutable class in hibernate?

Instances of an immutable class cannot be modified once they are created. You can refer to the following syntax to declare an immutable class for Hibernate in Java.

@Entity
@Table(name = "persons")
public final class ImmutablePerson {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private Long id;
   
   @Column(name = "first_name")
   private final String firstName;
   
   @Column(name = "last_name")
   private final String lastName;
   
   // Constructors, getters for firstName and lastName...
}

 

Here, we have declared a Hibernate entity/class with the final keyword which means it cannot have any subclasses. We have also used annotations to provide metadata to the Hibernate framework.

Q18: What is the role of the Hibernate Configuration object?

The Hibernate Configuration object is used to configure Hibernate and to specify the mapping between Java objects and database tables. It provides methods for the following functions-

  • Set configuration properties.
     
  • Specify mapping files or annotations.
     
  • Build the Hibernate SessionFactory.

Q19: How does Hibernate manage database connections, and what configuration options are available for connection pooling?

Hibernate manages database connections using a connection pool. A connection pool is a cache of database connections reused for multiple database operations. Hibernate is equipped with configuration options for managing the connection pool size and the maximum number of connections.

Also see, Azure Data Engineer Interview Questions

Q20: In Hibernate, identify the four ORM layers.

The four ORM layers in Hibernate are:

  • Pure relational
     
  • Full Object Mapping
     
  • Light Object Mapping
     
  • Medium Object Mapping

Advanced-Level Hibernate Interview Questions

Here we kick off with the Advanced Level Hibernate Interview Questions.

Q21. How does Hibernate differ from other Object-Relational Mapping (ORM) frameworks?

One of the main differences between Hibernate and other ORM frameworks is that it offers a powerful and flexible query language called Hibernate Query Language (HQL). It allows developers to write database queries using object-oriented syntax rather than SQL. Additionally, Hibernate offers features, such as automatic schema generation, that make it extremely popular among Java developers.

Q22. What is the difference between eager Loading and lazy Loading in Hibernate?

Eager Loading is a strategy where associated entities are loaded together with the parent entity. In standard terms, when a query is executed, Hibernate retrieves all the required data in a single query. On the other hand, we apply a lazy loading strategy when we are not using inter-related queries, meaning it is only loaded once explicitly requested.

Q23. Explain the concept of Hibernate Envers.

Hibernate Envers is an auditing framework that allows developers to track entity changes over time. This feature is handy when we are facing debugging issues in a project. Envers provides a variety of query and reporting tools that make it easy to access and analyze the revision history of an entity. Developers can easily compare different revisions of an entity and view changes.

Q24. How do you optimise Hibernate queries to improve performance?

The following ways are helpful to optimise Hibernate queries-

  • Use lazy Loading to reduce the data retrieved from the database at once.
     
  • Use caching to reduce the number of database queries required.
     
  • Use batch fetching to retrieve multiple entities in a single query.
     
  • Use indexes on frequently queried columns to improve query performance.

Q25: What are the concurrency strategies available in hibernate?

The following are some concurrency strategies available in hibernate:-

  • Versioned Optimistic Locking: This strategy involves adding a version attribute (e.g., a version number or timestamp) to the entity.
     
  • Timestamp-based Versioning: This strategy uses a timestamp instead of a version as an attribute for entities.
     
  • Pessimistic Locking: Pessimistic locking involves acquiring locks on database records when reading them to prevent concurrent updates. These locks are held until a transaction is committed or the lock is explicitly released.

 

These strategies are commonly used for managing concurrent access to database records by multiple users or threads.

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Q26: Explain the role of the Hibernate Persistence API (JPA).

 The Hibernate Persistence API, or JPA, is a specification for ORM frameworks developed by the Java Community Process (JCP). The JPA specification defines a set of standard annotations and interfaces to map Java objects to relational database tables.

Q27: What are the benefits of using annotations over XML configuration files?

 Some of the benefits of annotations include the following:

  • Conciseness
     
  • Compile-time checking
     
  • Better integration with IDEs
     
  • Reduced configuration complexity

Q28: Explain the purposes of Hibernate filters.

Hibernate filters allow developers to limit the results of a query. They can be used to filter out unwanted data or to apply security restrictions. Filters are defined in the Hibernate mapping files and applied to any query for that entity.

Q29: What is the difference between detached and transient objects in Hibernate?

In Hibernate, a transient object is non-persistent. Changes will not be saved to the database. On the other hand, a detached object is an object that is no longer associated with a Hibernate session.

Q30: How do you configure Hibernate to work with a distributed environment?

To configure Hibernate to work with a distributed environment , there are a few key considerations:

  • Connection pooling:
     
  • Cache configuration:
     
  • Database locking:
     
  • Configuration management:

Frequently Asked Questions

What are the three types of Hibernate?

The three types of Hibernate object states are – Transient Object State, Persistent Object State, and Detached Object State. These states are also called the lifecycle states of an object.

Is Hibernate Session thread safe?

Hibernate Session objects should not be used in the multi-threaded environment as they are not thread-safe, i.e., a new thread cannot be passed in hibernate session. Therefore, objects from a particular session can only interact with their own session.

Why Hibernate over JDBC?

The Hibernate framework abstracts low-level JDBC operations, which reduces the boilerplate code, and enhances productivity while allowing developers to work with Java objects instead of raw SQL. This simplifies the interaction with the database and increases the maintainability of the codebase.

What are the Hibernate interfaces? 

The Hibernate framework provides key interfaces like SessionFactory, Session, Transaction, and Criteria for database interaction. SessionFactory creates sessions, Session represents a unit of work, Transaction manages transactions, and Criteria helps with dynamic queries.

Conclusion

In the article, we discussed the top 30 Hibernate Interview Questions and Answers. We hope this blog has helped you enhance your knowledge regarding Hibernate Framework.
Please refer to the following blogs to learn more about Hibernate Interview Questions and other aspects of this framework.

Happy Reading!

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