Do you want to get hired as a Java Developer or Full Stack Developer? Is your job interview date approaching? Are you anxious about handling JPA questions that could be asked in your interview? Do you want to ensure that you have practised enough JPA Interview Questions? Well, we are here to assist you. We have brought you a compilation of hand-picked JPA Interview Questions that could be asked in your interview.
JPA stands for Jakarta Persistence API (formerly known as Java Persistence API). It is the Object Relational Mapping specification of Java. And this is used to store, manage, and access objects of Java in relational databases and databases such as NoSQL. JPA is neither a tool nor a framework. Rather, it's a specification of Java that allows the specific Java objects to be persisted. Java Persistence API's first version- JPA 1.0, was released in 2006. It was a part of the EJB (Enterprise JavaBeans) 3.0 specification. And since then, several versions have been released. In 2019, JPA got adopted as an independent Jakarta EE project.
Given below are some useful facts and insights on Jakarta Persistence API:
As per Statista reports, Java was among the top 5 most used languages in 2021, with a market share of 35.5% around the world.
The average salary of a Java Developer in the USA is around $57.75 per hour or $112,605 per annum. The salary ranges from the entry-level salary of $95,022 per annum to $146,250 per annum for experienced professionals.
Now that we have acquired basic knowledge and background of JPA. Then we will move to the JPA Interview Questions - updated (2022) for each of the following two sections separately:
Top 10 JPA Interview Questions
The Entity is a persistent domain object which is lightweight. The Entity is the main program entity. And additional classes can also be used by it, which can further be used to maintain the state of the Entity or auxiliary classes.
The entity class can inherit from other entity classes as well as the non-entity classes.
There are two elements of JPA that it can work upon. First are the properties (property) of classes that are designed like that of JavaBeans. And the second is the fields (field) or the class variables. Both these elements- property and field are the attributes of the entity class.
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The given attributes are valid in entity class:
An embeddable class cannot be used by itself. Both single embedded classes, as well as collections, can be contained in an entity class. We can use them as a map or key values also. Each embedded class belongs to just one object of the entity class at run time. And we can't use it for transferring data among the objects of entity classes. It serves the purpose of making definitions of common attributes for several entities.
The list of such attributes is given below:
The following requirements are set by JPA:
The four lifecycle statuses of an entity object are given below:
New- The object is created. But the primary keys have not been generated, and the object hasn't been saved yet.
Managed- The object is created. Also, the primary keys have been generated, and it's managed by JPA.
Detached- The object is created, but the JPA doesn't manage it.
Removed- The object is created as well as managed by JPA, but it will get deleted after the transaction is committed.
An API is described by this EntityManager interface for Entity's all basic operations and also of other JPA entities.
The main functions of EntityManger are given below:
The Entity is inherited from this Mapped Superclass only. Because it is not exactly the Entity, it doesn't need to fulfil the requirements set for the Entity. We can't use this class in Query operations or EntityManager. And it must be described in an XML file and marked with the annotation of Mapped Superclass.
The mapping strategies are the way of working with JPA with the entity-derived classes. The three types of inheritance strategies provided are:
The following four types of connections are available:
The following two types of fetch strategies are available in JPA
There are two types of cache in JPA:
The access type for an entity class, embeddable, superclass, or individual attributes is defined by it. This defines the way JPA refers to entity attributes such as class properties or class fields having setters and getters.
The simplest type of mapping of data on a column of the database is indicated by the basic annotation. Also, the fetch field access strategy, as well as the requirement of the field, can be specified in the annotation parameters.
The six types of locks are listed below in the ascending order of their reliability:
The following five options are there:
The Metamodel interface is used by JPA for this purpose. We can obtain this interface's object using the method of getMetamodel from an EntityManger or EntityMangerFactory.
The implicit polymorphism strategy is present in Hibernate but not in JPA.
JPQL is almost similar to SQL, but the names of entity classes and the attributes are used instead of the database columns. Also, the data types of entity attributes are used by the query parameters instead of database fields. And there is automatic polymorphism in JPQL, unlike SQL. KEY, TREAT, VALUE, MAP, and ENTRY are some of the unique functions of JPQL.
This means that regardless of the inheritance strategy, the objects of all the descendant classes are returned in each entity request.
We can use the TYPE function in the where condition for turning polymorphism off in JPQL.
Several major companies use Java around the world, such as:
Some of the most popular alternatives to Java are given below:
The main advantages of using JPA are given below:
No, JPA is just a specification. These tasks are performed, and the JPA specification is implemented by the ORM tools, including iBatis, Hibernate, and TopLink.
Some of the object-relational mapping frameworks are given below:
The object-relational mapping is a process that we use for developing and maintaining the relationship between the relational database and an object. This is achieved by mapping into the database column an object. The attributes of programming code get converted into the table columns by these object-relational mappers. Various database operations like updating, inserting, deleting, etc., can be managed by these mappers.
Hibernate falls under the category of most popular open-source implementations with the latest specification-JPA 2.1. Not only popular, but it is also considered the standard implementation. On the other hand, the task of JPA is describing the rules and APIs while Hibernate implements these descriptions. Just like several other implementations, Hibernate also has some additional features that are not described in JPA.
Generally, the java objects mapping into only relational databases are mentioned. Still, several NoSQL databases can be implemented, such as DataNucleus, Kundera, and ObjectDB, among others. Originally, all the specification-specific features could not be transferred completely to the NoSQL databases.
JDO and JPA both are the specifications to store objects of Java in databases. JDO is a more general specification describing the object-relational mapping for all possible repositories and bases.
Although the API of JDO and JPA don't match, JPA can be viewed as a component of JDO that is meant for relational databases mainly.
While JPA is still developed by JSR, JDO is now developed by the Apache JDO project.
The core concepts of JPA are listed below:
Java is one of the most used languages all around the world. And the Jakarta Persistence API (JPA) enhances its usability even further. This makes it a valuable skill to gain. And hence, a vast pool of opportunities is available in this field. We hope this JPA Interview Questions compilation can help you get the most out of this opportunity available and crack your interview.
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Kalla Saikumar is a technology expert and is currently working as a content associate at MindMajix. Write articles on multiple platforms such as ServiceNow, Business Analysis, Performance Testing, Mulesoft, Oracle Exadata, Azure, and other courses. And you can join him on LinkedIn.
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