Interview Questions and Answers for 'C' | Search Interview Question

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Q781. How is HashSet maintained in memory by Java ?

Ans. HashSet is maintained as HashMap by Java with values of the HashSet as Keys of the HashMap and value of the HashMap as the constant PRESENT.

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Q782. What is Closeable ?

Core Java

Ans. A Closeable is an interface which is a source or destination of data that can be closed.

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Q783. What is the difference between JPA and Hibernate ?

Hibernate

Ans. JPA or Java Persistence API is a standard specification for ORM implementations whereas Hibernate is the actual ORM implementation or framework.

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Q784. What is the advantage of JPA ?

Database

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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Not frequently asked as it was introduced with Java 8.

Q785. What is the @FunctionalInterface annotation ?

Core Java

Ans. This is an informative annotation that specify that the interface is a functional interface. A Function Interface has only one abstract method and many default methods. Compiler generates an error if the interface specified with the annotation doesn't abide by the specifications for functional interface.

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Q786. Name some Java REST services frameworks ?

Rest

Ans. Jersey , Restlet , RestX, Spring , RestEasy ,Restfulie, Play Framework

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Q787. Is this valid in Java ?

Long x = new Long ("42");

Core Java

Ans. Yes. Long wrapper class has overloaded constructor which takes String as input and then translate it to the long value and stored it as long.

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Q788. What is the use of !! command ? Can I use it with conjunction to some other string to complete a command ?

Unix

Ans. Its used to execute last command. Yes this can be used with other string to execute new command. For eg - if ls was the last command, We can execute !! -l for having the long listing.

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Q789. What is classpath in a project?

Core Java

Ans. ClassPath is the path where Java looks for class files to resolve the dependencies. For example - If you are using a class "xyz" in your code and have specified the respective import, Where should Java look for the definition of xyz. Java determines using the class path settings.

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Q790. Why is a constant defined as a static final in Java?

Core Java

Ans. Final makes sure that the value doesn't change after initialization and static makes sure that there is only one copy that can be shared across objects.

Making it non static will unnecessarily create a different copy per object wherein the same value will kept for all copies ( as its final and cannot be changed ).

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Q791. What is the difference between public class and class ?

Core Java

Ans. Class without any access specifier has the default scope i.e it can be accessed by any class within same package.

Class declared public can be accessed from anywhere.

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Q792. Which version control (VC) or software configuration management (SCM) systems work with Merge?

Scm

Ans. You can use Tortoise SVN,which has Merge Utility embedded in it.

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Q793. .Can you uninstall an older version of Merge before installing a newer version or build?

Ans. NA

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Q794. What things you will look for if you get following exception while making DB call ?

table or view does not exist

Database

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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Q795. What's the benefit for specifying constraints like Not Null , Primary Key explicitly instead of specifying it against the column ?

Database

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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Q796. How can we disable a constraint ?

Database

Ans. alter table
table_name
DISABLE constraint
constraint_name;

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Q797. Can we have foreign key reference to a non primary key column ?

Database

Ans. Yes, but the respective key in the foreign table should be declared Unique.

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Q798. What should be done for auto generating primary key id in a table ?

Database

Ans. We need to create a sequence.

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Q799. Which constraint cannot be specified as an explicit constraint and should be specified with the column only ?

Database

Ans. NOT NULL

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Q800. How can we see Dependencies for the project and where exactly they are defined ?

Maven

Ans. Using

mvn dependency:tree

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Q801. What are the benefits of transitive depency in Maven ?

Maven

Ans. Transitive dependencies allows to avoid specifying the libraries that are required by the project which are specified in other dependent projects - Remote or Local.

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Q802. Will this code compile ?

public class BuggyBread1{
abstract public void test();
}

Core Java

Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class".

We need to declare the class abstract for it to have any abstract method.

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Q803. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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Q804. Give an Example for Builder Pattern ?

Core Java

Ans. String str = new StringBuilder().append("Buggy").append("Bread").toString();

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Q805. Is this Polymorphism ?

Map<String, List<String>> inventoryManagerCountMap = new HashMap<String, ArrayList<String>>();

Core Java

Ans. No. This will result in compilation error as Polymorphism cannot be performed on Object types.

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Q806. How to know the structure of a Table in Oracle ?

Database

Ans. DESC

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Q807. How to know the constraints on a Table in Oracle ?

Database

Ans. SELECT *
FROM user_constraints
WHERE table_name = ''

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Q808. How to know the default column value of a Table in Oracle ?

Database

Ans. Select DATA_DEFAULT
from DBA_TAB_COLUMNS
where TABLE_NAME = '' and COLUMN_NAME='';

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Rarely asked as it was introduced with Java 8.

Q809. Difference between DoubleSummaryStatistics , IntSummaryStatistics and LongSummaryStatistics ?

Core Java

Ans. They all does the same task i.e to compute statistical information on the stream of data. They differ by the way they store the statistical information as they expect a different data type of the values being used.

IntSummaryStatistics and LongSummaryStatistics expect non floating point values and hence stores the statistical information like min,max and sum as non floating values ( int or long ) whereas DoubleSummaryStatistics stores these information as floating value.

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Q810. Have you ever used StringTokenizer ?

Core Java

Ans. No, Alternatively I have used String.split("\\s") for achieving the same function.

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