Hibernate - Interview Questions and Answers for 'Abs' | Search Java Interview Question

Hibernate - Interview Questions and Answers for 'Abs' - 15 question(s) found - Order By Newest

Frequently asked question in companies using Hibernate.

Q1. What is Lazy Initialization in Hibernate ?

Hibernate

^{Admin
info@buggybread.com}

Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded.

Sample Code for Lazy Initialization

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Q2. What things you would care about to improve the performance of Application if its identified that its DB communication that needs to be improved ?

Solution

^{Admin
info@buggybread.com}

Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements )

2. Restructuring Indexes.

3. DB Caching Tuning ( if using ORM )

4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM )

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Very frequently asked Hibernate interview question. Frequently asked in TCS ( based on 2 feedback )

Q3. What are different types of associations in Hibernate ?

Hibernate

^{Admin
info@buggybread.com}

Ans. There are 4 types of associations in Hibernate

One to One
One to Many
Many to One
Many to Many

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Q4. What is the use of @GeneratedValue annotation in Hibernate?

Hibernate

^{Admin
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Ans. This annotation is added to the auto increment column with the strategy to increment the column value. Usually this is added to the surrogate primary key column and specified with the Database Sequence.

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Q5. Write a program to show thread usage in Java by implementing runnable interface

^{2017-08-03 12:16:07}

Ans. public class MyClass {
   static class MyThreadClass implements Runnable{

      public void start() {
         Thread t = new Thread(this,"threadName");
         t.start();
      }

      @Override
      public void run() {
         System.out.println("Hello");
         try {
            Thread.sleep(1000);
            System.out.println("Hello Again");
         } catch (InterruptedException e) {
            e.printStackTrace();
         }

      }

   }

   public static void main(String[] args){
      MyThreadClass myThreadClass = new MyThreadClass();
      myThreadClass.start();

      MyThreadClass myThreadClass2 = new MyThreadClass();
      myThreadClass2.start();
   }
}

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Q6. What is the difference between these 2 annotations ?

@Entity ( name ="EMPLOYEES")
@Entity @Table ( name=""EMPLOYEES"" )

@Entity ( name="EMP")
@Table ( name="EMPLPYEES" )

Hibernate

^{Admin
info@buggybread.com}

Ans. First Annotation will set the Entity name as EMPLOYEES and hence will try to map with the same Table name.

The second annotation will make the Entity mapped to table EMPLOYEES irrespective of the Entity Name ( which is class name in this case ).

Third Annotations will set the different names for Enitity and Table and will explicitly map them.

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Q7. What is the advantage of JPA ?

Database

^{Admin
info@buggybread.com}

Ans. Its a specification that guides the implementation of ORM frameworks. Implementations abiding by the specification would mean that one can be replaced with other in an application without much hassle. Only the Features that are added over the specification needs to be taken care of if any such change is made.

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Q8. How do we specify the criteria if it involves mapping between two entities or join between tables ?

Hibernate

^{Admin
info@buggybread.com}

Ans. The following code returns the list of Employee objects having employee name starting with A and Dept Name ( Department , Employee Mapped ).

session.createCriteria(Employee.class,"emp")
.createAlias("emp.department", "dept",Criteria.INNER_JOIN)
.add( Restrictions.like("name", "A%") )
.add(Restrictions.eq("dept.name","Finance")
.list();

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Q9. Difference between JDBC and Hibernate ?

Database

^{2016-12-06 09:57:14}

Ans. JDBC is a standard Java Api for Database communication whereas Hibernate is an ORM framework that uses JDBC to connect with Database.

Hibernate is another layer of object table mapping over JDBC that provide a database independent, object oriented and an efficient way of database communication.

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Q10. What are the methods to connect to database in Java ?

Database

^{2017-02-05 09:00:41}

Ans. JDBC ( Java Database Connectivity ),ODBC (Open Database Connectivity), Hibernate, JPA ( Java Persistence API ), JOOQ,MyBatis

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Q11. What is the difference between JDBC, Hibernate and ODBC ?

Database

^{2017-06-18 17:52:39}

^{This question was recently asked at 'Oracle Argentina'.This question is still unanswered. Can you please provide an answer.}

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Q12. Which jar files need to be included for using Hibernate ?

Hibernate

^{2018-07-23 11:25:33}

Ans. hibernate-orm
hibernate-validator
hibernate-ogm
hibernate-search

or you can download hibernate core with all dependencies.

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Q13. Explain Hibernate caching mechanism

Hibernate

^{2018-11-14 12:53:50}

Ans. Every fresh session having its own cache memory, Caching is a mechanism for storing the loaded objects into cache memory. The advantage of cache mechanism is, whenever again we want to load the same object from the database then instead of hitting the database once again, it loads from the local cache memory only, so that the no. of round trips between an application and a database server got decreased. It means caching mechanism increases the performance of the application.

In hibernate we have two levels of caching

First Level Cache [ or ] Session Cache
Second Level Cache [ or ] Session Factory Cache [ or ] JVM Level Cache

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Q14. Write a Program to swap 2 variables ( using 3rd variable )

Core Java

^{2017-07-25 19:41:20}

Ans. int x = 1;
int y = 2;
int z = x;
x = y;
y = z;

System.out.println("x="+x);
System.out.println("y="+y);

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Q15. Write a Program to swap two variables ( without using 3rd variable )

^{2017-07-25 19:42:32}

Ans.
int x = 1;
int y = 2;

x = x+y;
y = x-y;
x = x-y;

System.out.println("x="+x);
System.out.println("y="+y);

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Q16. Which method needs to be implemented if a class is implementing comparable interface ?

Core Java

a. comp

b. compare

c. compareTo

d. compareEquals

Ans.c. compareTo

Q17. What is Dirty Read in Database Transactions ?

Database

a. Data Read by Transaction 2 which hasn't yet updated by Transaction 1

b. Data Read by Transaction 2 which has been updated and commited by Transaction 1

c. Data Read by Transaction 2 which has been updated but not commited by Transaction 1

d. Inability of Transaction 2 to read Data when Transaction 1 is updating.

Ans.c. Data Read by Transaction 2 which has been updated but not commited by Transaction 1

Q18. Which of the following is not true for abstract classes ? Reference

Core Java

a. Abstract Class is only meant to be sub classed and not supposed to be instantiated.

b. Abstract class handlers can be used to handle derived class objects.

c. We can't have an abstract class without abstract methods.

d. Abstract class has member elements.

Ans.c. We can't have an abstract class without abstract methods.

Q19. Which of the following class creates immutable objects ? Reference

Core Java

a. String

b. StringBuffer

c. StringBuilder

d. None of these create immutable objects.

Ans.a. String

Q20. Which of the following can be declared abstract ?

Core Java

a. static methods

b. instance methods

c. static variable

d. instance variables

Ans.b. instance methods

Q21. In majority of the cases, the following join will give maximum number of results ? Reference

Database

a. Inner Join

b. Outer Join

c. Left Join

d. Right Join

Ans.b. Outer Join

Q22. Which if the following is true for SQL Joins ? Reference

Database

a. Left Join and Right Join gives equal number of Results

b. Outer Join and Inner Join gives equal number of Results

c. Inner Join gives maximum number of results records

d. Inner Join gives minimum number of result records

Ans.d. Inner Join gives minimum number of result records

Q23. Which of the following is not true for Prepared Statements ?

Database

a. Prepared Statements provides better performance

b. Prepared Statements prevent SQL Injection attacks

c. Prepared Statements provide ORM capabilities

d. Prepared Statement provides DB side caching

Ans.c. Prepared Statements provide ORM capabilities

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