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

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Q1831. Can I use different Java versions for building different Eclipse projects ?

Eclipse

Ans. Yes. We can assign different JRE System libraries by going to

Java Build Path -> Libraries

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Q1832. How to perform a clean install without executing Tests ?

Maven

Ans. mvn clean install -Dmaven.test.skip=true

or

mvn install -DskipTests

or

org.apache.maven.plugins
maven-surefire-plugin

true

within parent POM file.

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Q1833. How to generate getters and setters automatically in eclipse ?

Eclipse

Ans. Right Click -> Source -> Generate Getters and Setters.

and it will open up a dialog wherein we can select the fields to generate Getters and Setters.

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Q1834. What are the considerations to be made in case of loops in Java ?

Core Java

Ans. 1. It shouldn't result in infinite loop. Please make sure that you have a condition that will terminate the loop and that condition should be reached.

2. Make sure to use the break statement if you aspire to only look for something. Not using break will unnecessarily execute it till the end of for loop in some cases.

3. Similarly use continue to execute the loop with next iteration and bypass the rest of the code block if required.

4. Try to avoid multiple nesting of for loops. If it''s required, Make sure to use break and continue properly so as to avoid some unnecessary processing.

5. Make sure to use try catch within the loop and not outside the for loop if you expect it to continue if one of the iteration fails.

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Q1835. Shouldn't we make a class with all static members is its just expected to be executed as a standalone program with just one thread. Moreover Lets assume that there is no runtime Polymorphism required and there is no need for serialization ?

Design

Ans. Still No in case we are making use of inheritance. we may have problem wherein we have program flow moving across common inherited method and specific methods of the derived class. call made to another static method in the parent class will only access the static class of the Parent class irrespective of the call from any of the derived class.

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Q1836. Tell me something about AssertionError ?

Core Java

Ans. AssertionError is actually a fatal fault or a bug in the program. We may not like to continue program , request or thread execution if this error occurs as this condition is the assumption to continue further execution.

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Q1837. Do you know of any DB statement that can be used if we would like to insert multiple rows into a table ?

Database

Ans. We can use INSERT ALL.

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Q1838. Why is null == null returns true ?

Core Java

Ans. Any reference in java that doesn't point to any object , gets assigned null i.e is a reference to null. Two object references in java are treated equal if they point to the same memory. That's Why null == null results true.

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Q1839. How is HashSet maintained in memory by Java ?

Core 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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Q1840. 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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Q1841. Why do we need Inner classes ? Cant we just work with outer classes wherever we implement Inner classes ?

Core Java

Ans. Yes, we can substitute outer classes wherever we need to have inner classes but Inner classes have advantage in certain cases and hence preferred -

Ease - Why to implement a class outside if its objects are only intended to be part of an outer object. Its easy to define the class within another class if the use is only local.

Protection - Making a call an outer exposes a threat of it being used by any of the class. Why should it be made an outer class if its object should only occur as part of other objects.

For example - You may like to have an class address whose object should have a reference to city and by design thats the only use of city you have in your application. Making Address and City as outer class exposes City to any of the Class. Making it an inner class of Address will make sure that its accessed using object of Address.

Sample Code for inner class

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Q1842. 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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Q1843. 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.

Q1844. 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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Q1845. 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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Q1846. 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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Not frequently asked as it was introduced with Java 8.

Q1847. Difference between final and effectively final ? Why is effectively final even required ?

Core Java

Ans. Final variable means a variable that has been declared final and hence cannot be de referenced after initialization. Effective final means a variable that has not been declared final but haven't been reassigned the value after initialization.

First is the regulation that restricts the reassignment and will raise a compilation error if we try to do so. Second is the outcome without the restriction.

Effective Final is the eventual treatment of the variable that is required for many features. For eq - Java 8 requires that local variables referenced from a lambda expression must be final or effectively final.It means all local referenced from lambda expressions must be such that their value shouldn't be changed after initialization whether declared final or not.

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Very Frequently asked.

Q1848. Explain throw, throws , try and catch in Java ?

Core Java

Ans. throw is used to re throw an exception.throws is used to declare that the method throws the respective exceptions.try block is used to identify if the respective block has thrown any exception.catch is used to catch the exception that has been thrown by the respective try block.

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Q1849. 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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Q1850. 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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Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews.

Q1851. What are the difference between composition and inheritance in Java?

Core Java

Ans. Composition - has-a relationship between objects.
Inheritance - is-a relationship between classes.

Composition - Composing object holds a reference to composed objects and hence relationship is loosely bound.
Inheritance - Derived object carries the base class definition in itself and hence its tightly bound.

Composition - Used in Dependency Injection
Inheritance - Used in Runtime Polymorphism

Composition - Single class objects can be composed within multiple classes.
Inheritance - Single class can only inherit 1 Class.

Composition - Its the relationship between objects.
Inheritance - Its the relationship between classes.

Sample Code for inheritance

Sample Code for composition

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Q1852. 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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Frequently asked to fresh graduates and less experienced.

Q1853. Why do we write public static void main ? Can we use some other syntax too for main ?

Core Java

Ans. 1. public is the access modifier that makes the method accessible from anywhere, static is the keyword that makes it accessible even without creating any object, void means it doesn't return anything , String args[] is the array of argument that the method receives.

2. If we use main without the string args , it will compile correctly as Java will treat it as just another method. It wont be the method "main" which Java looks for when it looks to execute the class and hence will throw

Error: Main method not found in class , please define the main method as:
public static void main(String[] args)

3. Main is not a keyword but a special string that Java looks for while initiating the main thread.

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Q1854. 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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Q1855. .Can you uninstall an older version of Merge before installing a newer version or build?

Ans. NA

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Q1856. 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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Q1857. 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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Q1858. How can we disable a constraint ?

Database

Ans. alter table
table_name
DISABLE constraint
constraint_name;

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Q1859. 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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Q1860. 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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