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Interview Questions and Answers for 'Oracle' - 35 question(s) found - Order By Newest

Frequently asked question in companies using Hibernate.
  Q1. What is Lazy Initialization in Hibernate ?Hibernate
Admin
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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 is a String Pool ?Core Java
Anonymous
Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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Basic and Very Frequently asked.
  Q3. What is Polymorphism in Java ?Core Java2016-11-06 09:10:54

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

  Sample Code for overloading

  Sample Code for overriding

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Advanced level question frequently asked in US based companies. Recently asked in EMC and Intuit.
  Q4. Can you provide some implementation of a Dictionary having large number of words ? Solution
Admin
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Ans. Simplest implementation we can have is a List wherein we can place ordered words and hence can perform Binary Search.

Other implementation with better search performance is to use HashMap with key as first character of the word and value as a LinkedList.

Further level up, we can have linked Hashmaps like ,

hashmap {
a ( key ) -> hashmap (key-aa , value (hashmap(key-aaa,value)
b ( key ) -> hashmap (key-ba , value (hashmap(key-baa,value)
....................................................................................
z( key ) -> hashmap (key-za , value (hashmap(key-zaa,value)
}

upto n levels ( where n is the average size of the word in dictionary.

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q5. What is a final method ?Core Java
Anonymous
Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class.

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 Q6. Can we access instance variables within static methods ?Core Java
Anonymous
Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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  Q7. Difference between Vector and ArrayList ?Core Java
Anonymous
Ans. Vectors are synchronized whereas Array lists are not.

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Very frequently asked in phone and walk in interviews.
  Q8. What are Marker Interfaces ? Name few Java marker interfaces ?Core Java
Anonymous
Ans. These are the interfaces which have no declared methods.Serializable and cloneable are marker interfaces.

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Frequently asked to fresh graduates.
 Q9. What is ACID ?Database2016-11-04 08:09:44

Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions.

Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback.

Consistency means that any transaction should lead database from one stabe state to another.

Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially.

Durability means that when a transaction is committed it forms the permanent state of database.

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Very frequently asked. Usually asked with questions related to String.
  Q10. What is an Immutable Object ?Core Java
Anonymous
Ans. Object that can't be changed after instantiation.

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 Q11. Is it necessary that each try block to be followed by catch block ? Core Java
Anonymous
Ans. It should be followed by either catch or finally block.

  Sample Code for Retry in case of exception

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Very frequently asked if being interviewed for hibernate. Frequently asked in Tata Consultancy (TCS) and Overstock.com
  Q12. Difference between load and get ?Hibernate
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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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  Q13. What is a self Join and give an example of a self Join ?

or

What is self Join and What is it's purpose ?
Database2016-06-30 20:13:35

Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.

Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count

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Frequently asked in CTS ( Based on 2 feedback )
  Q14. What is the difference between comparable and comparator in java.util pkg?Core Java
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Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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 Q15. How finally used under Exception Handling?Core Java
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Ans. The finally keyword is used to create a block of code that follows a try block. A finally block of code always executes, whether or not an exception has occurred.

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 Q16. What things you will look for if you get following exception while making DB call ?

table or view does not exist
Database
Admin
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Ans. First will check if the table or view actually exist in the DB

If it does , Will make sure to see that the application has rights on the schema that holds the respective Table.

Will then make sure that we have prefixed the schema with the table name while accessing it.

Will then make sure that its not DB Cache that's causing it as the table DDL might have been created recently.

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 Q17. What's the benefit for specifying constraints like Not Null , Primary Key explicitly instead of specifying it against the column ?Database
Admin
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Ans. In case we specify them explicitly we can have control over constraint name as otherwise they will be system generated. It provides an ease in case we plan to drop the constraint in future.

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 Q18. How can we disable a constraint ?Database
Admin
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Ans. alter table
table_name
DISABLE constraint
constraint_name;

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 Q19. Can we have foreign key reference to a non primary key column ?Database
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Ans. Yes, but the respective key in the foreign table should be declared Unique.

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 Q20. What should be done for auto generating primary key id in a table ?Database
admin
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Ans. We need to create a sequence.

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 Q21. Which constraint cannot be specified as an explicit constraint and should be specified with the column only ?Database
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Ans. NOT NULL

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 Q22. How to know the structure of a Table in Oracle ?Database
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Ans. DESC

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 Q23. How to know the constraints on a Table in Oracle ?Database
Admin
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Ans. SELECT *
FROM user_constraints
WHERE table_name = ''

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 Q24. How to know the default column value of a Table in Oracle ?Database
Admin
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Ans. Select DATA_DEFAULT
from DBA_TAB_COLUMNS
where TABLE_NAME = '' and COLUMN_NAME='';

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  Q25. What is a Database Trigger ?Database2016-10-18 11:31:17

Ans. A trigger is a special kind of stored procedure that automatically gets executed upon an event in the database server.

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 Q26. Have you heard about the external table feature of Oracle ?Database2016-10-18 11:48:05

Ans. The external tables feature is a complement to existing SQL Loader functionality. It enables to access data in external sources as if it were in a table in the database. We have used it few times for replicating tables across different database systems.

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 Q27. What was the driving force to introduce default methods in Interfaces wef from Java 8 ?Core Java2016-07-14 14:36:49

Ans. Earlier any class implementing an interface was supposed to implement all methods declared in an interface. There was no place for optionally implementing all or subset of methods.Though we have abstract classes wherein we could have provided such a mechanism by declaring some methods as abstract while providing definition for some. But as Abstract classes have a body and are comparatively heavier than interfaces and interfaces associate closely to the concept of providing interfacing than abstract classes, Java might have though of providing optional implementation for default methods. This way same interface can be reused in variety of ways rather than making copies of an interface to suit different needs.

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 Q28. Difference between JDBC and Hibernate ?Database2016-12-06 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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  Q29. What is database Normalization ?Database2017-01-09 12:00:02

Ans. https://en.wikipedia.org/wiki/Database_normalization

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 Q30. What is the difference between Oracle , Cassandra and Redis ?Database2017-05-22 17:12:03

Ans. Oracle is a relational database. Cassandra is a noSQL Database whereas Redis is an inmemory cache.

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 Q31. What is the order in which triggers gets fired ?Database2017-05-24 20:38:35

Ans. There is no specific order in which database fires the triggers if they are for the same operation. If we need to have a specific order for their execution, we should have them all in a stored procedure and the procedure should get executed upon the event.

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 Q32. What is the difference between JDBC, Hibernate and ODBC ?Database2017-06-18 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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 Q33. How different is the Search algorithm when we query Cassandra Tables and When we query Oracle Tables ?Cassandra2017-08-18 09:40:40

Ans. Relational Database uses linear search if we don't query using indices. Performance for linear search is O(n). If indices have been used , relational database uses binary search. Performance for binary search is O(Log n).

Casandra uses hash search. Performance for Hash Search is O(1).

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 Q34. Can we override wait() or notify() ?Core Java2017-09-13 14:17:15

Ans. No, because these are final.

public final void wait() throws InterruptedException

public final void notify()

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 Q35. How did you use Spring in your project ? Which Spring annotations have you used in your project ?Spring2019-01-12 18:23:06

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


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