Interview Questions and Answers for 'T' | Search Interview Question

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Q2221. Please specify in what sequence the objects of following classes will be created ?

Session , SessionFactory, Query , Configuration

Hibernate

Ans. Configuration -> SessionFactory -> Session -> Query

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

Q2222. What are different types of associations in Hibernate ?

Hibernate

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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Q2223. What are the configuration files in Hibernate ?

Hibernate

Ans. hibernate.cfg.xml ( Main Configuration File )

and *.hbm.xml files ( Mapping Files )

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Q2224. What are the contents of Hibernate configuration file ( hibernate.cfg.xml ) ?

Hibernate

Ans. HBM Files ( Mapping )
DB Connection ( DB Connection String , User Name , Password , Pool Size )
SQL Dialect ( SQL variant to be generated )
Show SQL ( Show / No show SQL on Console )
Auto Commit ( True / False )

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Q2225. What are the Core Interfaces of Hibernate Framework ?

Hibernate

Ans. Configuration
SessionFactory
Session
Transaction
Query and Citeria

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Q2226. What are collection types in Hibernate ?

Hibernate

Ans. Bag, Set , List , Array, Map

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Very frequently asked if being interviewed for hibernate. Frequently asked in Tata Consultancy (TCS) and Overstock.com

Q2227. Difference between load and get ?

Hibernate

Ans. If id doesnt exist in the DB load throws an exception whereas get returns null in that case.get makes the call to DB immediately whereas load makes the call to proxy.

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Q2228. What is lazy fetching in Hibernate ?

Hibernate

Ans. Lazy fetching is the technique of not loading the child objects when parent objects are loaded. By default Hibernate does not load child objects. One can specify whether to load them or not while doing the association.

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Q2229. Different types of Hibernate Instance States ?

Hibernate

Ans. Transient - In this state, an instance is not associated with any persistence context
Persistent - In this state, an instance is associated with a persistence context
Detached - This is a state for an instance which was previously associated with a persistence context an has been currently closed dissociated

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Q2230. Is It Good to use Reflection in an application ? Why ?

Core Java

Ans. no, It's like challenging the design of application.

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Q2231. Why is Reflection slower ?

Ans. Because it has to inspect the metadata in the bytecode instead of just using precompiled addresses and constants.

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Q2232. When should we use prototype scope and singleton scope for beans ?

Spring

Ans. We should use singleton scope for beans when they are stateless and prototype when they are stateful.

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Q2233. Difference between Assert and Verify ?

Testing

Ans. Assert works only if assertions ( -ea ) are enabled which is not required for Verify.Assert throws an exception and hence doesn't continue with the test if assert evaluates to false whereas it's not so with Verify.

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.

Q2234. What is the difference between ArrayList and LinkedList ?

Core Java

Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

Sample Code for ArrayList

Sample Code for LinkedList

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Q2235. Which class elements are not persisted ?

Hibernate

Ans. Static and Transient.

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Q2236. Which annotations are used in Hibernate ?

Hibernate

Ans. @Entity
@Table
@Id
@Column
@Temporal
@Basic
@Enumerated
@Access
@Embeddable
@Lob
@AttributeOverride
@Embedded
@GeneratedValue
@ElementCollection
@JoinTable
@JoinColumn
@CollectionId
@GenericGenerator
@OneToOne
@OneToMany
@ManyToOne
@ManyToMany
@NotFound

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Q2237. What entries we make in the hibernate config file if we are not using hbm files but Annotations ?

Hibernate

Ans. We configure Entity classes having annotated mappings.

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Q2238. How many SessionFactory and Session objects are created ?

Java EE

Ans. Single SessionFactory object and multiple session objects for opening different session. Hibernate creates new Session object per thread.

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Q2239. What is the way to rollback transaction if something goes wrong using hibernate API ?

Hibernate

Ans. We can have the code calling Hibernate API within try block and can have transaction.rollback within Catch.

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Q2240. What is the use of hbm2ddl Configuration in Hibernate ?

Hibernate

Ans. This configuration specifies if hibernate should creates the Schema / Table on its own if the respective table is not found.

"update" doesn't create the table if it's not found whereas configuration set as "create" creates the schema automatically.

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Q2241. What is the difference between these 2 annotations ?

@Entity

@Entity ( name="EMPLOYEES" )

Hibernate

Ans. The first annotation will try to map the Class with the Table as of same name as Class whereas the second annotation will specify the Entity name as "EMPLOYEES" and hence will try to map with Table Name "EMPLOYEES".

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Q2242. What is the difference between these 2 annotations ?

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

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

Hibernate

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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Q2243. What are the different ID generating strategies using @GeneratedValue annotation ?

Hibernate

Ans. Auto , Identity , Sequence and Table.

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Q2244. How to do Eager loading in Hibernate ?

Hibernate

Ans. Using

lazy = false in hibernate config file

or

@Basic(fetch=FetchType.EAGER) at the mapping

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Frequently asked question in companies using Hibernate.

Q2245. What is Lazy Initialization in Hibernate ?

Hibernate

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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Q2246. What are the ways to avoid LazyInitializationException ?

Hibernate

Ans. 1. Set lazy=false in the hibernate config file.

2. Set @Basic(fetch=FetchType.EAGER) at the mapping.

3. Make sure that we are accessing the dependent objects before closing the session.

4. Force initialization using Hibernate.initialize

5. Using Fetch Join in HQL.

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Q2247. What is cascade ?

Hibernate

Ans. Instead of Saving Parent as well as Child Entities individually , Hibernate provides the option to persist / delete the related entities when the Parent is persisted.

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Q2248. What are the different Cascade types ?

Hibernate

Ans. Detach, Merge , Persist , Remove , Refresh

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Q2249. Which type of associated Entities are Eagerly loaded by Default ?

Hibernate

Ans. OneToOne

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Q2250. After which Hibernate version , related Entities are initialized lazily ?

Hibernate

Ans. After Hibernate 3.0

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