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

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Q721. Can we have null keys in TreeMap ?

Core Java

Ans. No, results in exception.

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Q722. Can value be null in TreeMap ?

Core Java

Ans. Yes.

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Q723. Which interface TreeMap implements ?

Ans. TreeMap implements NavigableMap, SortedMap, Serializable and Clonable.

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Q724. Do we have form beans in Struts 2 ?

Ans. No, because they are not longer required. As action classes are no more singleton in Struts 2, user inputs can be captured in action itself.

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Q725. What the Bean scopes provided by Spring ?

Spring

Ans. Singleton , Prototype , Request , Session , global-session

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Q726. What are the various Auto Wiring types in Spring ?

Ans. By Name , By Type and Constructor.

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Q727. What are the the methods to clear cache in Hibernate ?

Hibernate

Ans. Evict() and clear(). Evist is used to clear a particular object from the cache whereas clear clears the complete local cache.

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Q728. What are different types of second level cache ?

Hibernate

Ans. 1. EHCache ( Easy Hibernate )
2. OSCache ( Open Symphony )
3. Swarm Cache ( JBoss )
4. Tree Cache ( JBoss )

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Q729. Can we disable first level cache ? What should one do if we don't want an object to be cached ?

Hibernate

Ans. No.We can either call evict after the object retrieval or can use separate sessions.

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Q730. What is Hibernate ?

Hibernate

Ans. Hibernate is a Java ORM Framework.

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Q731. What are the different types of inheritance in Hibernate ?

Hibernate

Ans. Table Per Class , Table per Sub Class , Table per Concrete Class

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Q732. 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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Q733. 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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Q734. 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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Q735. 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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Q736. 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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Q737. 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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Q738. Which class elements are not persisted ?

Hibernate

Ans. Static and Transient.

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Q739. 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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Q740. 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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Q741. 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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Q742. 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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Q743. 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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Q744. What are the different ID generating strategies using @GeneratedValue annotation ?

Hibernate

Ans. Auto , Identity , Sequence and Table.

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Q745. 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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Q746. 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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Q747. What are the different Cascade types ?

Hibernate

Ans. Detach, Merge , Persist , Remove , Refresh

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Q748. Which type of associated Entities are Eagerly loaded by Default ?

Hibernate

Ans. OneToOne

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Q749. After which Hibernate version , related Entities are initialized lazily ?

Hibernate

Ans. After Hibernate 3.0

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Q750. Can we declare Entity class as final ?

Hibernate

Ans. Yes but as Hibernate creates the Proxy Classes inherited from the Entity Classes to communicate with Database for lazy initialization. Declaring entity classes as final will prohibit communication with database lazily and hence will be a performance hit.

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