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Interview Questions and Answers - Order By Newest

Q531. Difference between == and === ?

Ans. == compares values === is used in scripting languages for comparing two values as well as there data tpe. like in js,php.

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Q532. Can we have multiple inheritance in java using abstract class ?

Core Java

Ans. No

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Q533. Describe structure of a Web application.

architecture

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Q534. What are the types of authentication used in Web services ?

Web Service

Ans. Encrypted User Name / Password
Encrypted Password within Cookie
Encrypted Tokens
IP
Client Certificates
Oauth

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Q535. Does use of Final class enforces composition over Inheritance in Java ?

Core Java

Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind.

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Q536. What could be the reasons for restricting inheritance using final class ?

Core Java

Ans. 1. Enforcing composition over inheritance
2. Restricting overriding of certain methods
3. Final methods are faster than regular instance methods
4. Enforcing Immutability

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Q537. Explain OAuth.

Authentication

Ans. OAuth is an open-standard authorization protocol or framework that describes how unrelated servers and services can safely allow authenticated access to their assets without actually sharing the initial, related, single logon credential. Like using Google or Facebook to login to something.

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Q538. Between Encrypted Password authentication and IP Authentication , which one would you prefer and why ?

Authentication

Ans. IP authentication is very restrictive, if IP changes for some reason then getting the new IP white listed on the server firewall could run your day pretty long. I would prefer encrypted password authentication cause it is not affected by IP changes and not limited to a white listed IP, I could use any different machine and get through authentication without any hassle.

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Q539. Write code to create a folder if it doesn't exist.

Core Java

Ans. File folder = new File(path);

if(!folder.exists()){
try {
folder.mkdir();

} catch (Exception e) {}
}

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Q540. Difference between Arrays and ArrayList ?

Core Java

Ans. Both Arrays and ArrayLists are used to store elements. Elements can be either primitives or objects in case of Arrays, but only objects can be stored in Arraylist. Array is a fixed length data structure while arraylist is variable length collection class. Once created, you cannot change the size of the arrays, but arraylists can dynamically resize itself when needed.Another notable difference between Arrays and Arrayslist is that arary is part of core java programming and array list is part of collection classes

Sample Code for arrays arraylist

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Q541. Can we declare an array without assigning the size of an array?

Core Java

Ans. No, It will throw compile time error saying "must provide either dimension expressions or an array initializer"

Alternatively we can provide array initializer like

String[] strArray = new String[]{"Buggy","Bread"};

which will initialize it to size 2 with values as "Buggy" and "Bread"

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Q542. What is meant by "unreachable code" ? Can you write a code segment explaining this ?

Core Java

Ans. Unreachable code is a code segment that can never be executed in any case. For example -

int x = 5;
return;
System.out.println(x);

In this code , 2nd line will return the control out of the method and hence 3rd line will never get executed and hence is unreachable code. This will be caught at compile time only.

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Q543. What is the difference between log4j and java logging api.

Log4j

Ans. log4j is by apache while java logging api is given by sun. log4j is more powerful,extensible and simple to use than java logging api.

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Q544. Why doesn't this code give compile time error when we are clearly trying to add an integer element to an array of Strings

Object[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. Because the reference is of Object Array and the resolution of what it holds is identified at the runtime.

String[] strArray = new String[2];
strArray[0] = 5;

would have given the compile time array as the reference is of String array.

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Q545. Difference between StoreModule.forRoot() and StoreModule.forFeature() ?

NgRx

Ans. forFeature is used for lazily registering reducers with the module.

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Q546. What would you do if you see an error thrown by a lambda function as "Access Denied" while doing something with S3 ?

Amazon Web Services (AWS)

Ans. Just like people , AWS resources too have execution roles or permissions. Seems like in such a situation Lambda function may not have sufficient privileges to perform operations on S3. For example - The execution role of Lambda may just have read permissions on S3 and we may be trying to perform PutObject operation.

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Q547. What will happen if there are no interfaces in Java ?

Core Java

Ans. Abstract classes can take care of that to a certain extent. Though they are little heavier than Interfaces but An abstract class with all abstract methods and no instance variables will be able to help with everything that currently an interface does.

The only problem is that a class can only extend one class whereas it can implements multiple interfaces and that is the reason Interfaces were introduced in Java, i.e to get over the problem of multiple inheritance.

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Q548. How to avoid cloning, serialization in the singleton class ?

Design

Ans. For Cloning-exception,For deserialization-read.resolve()

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Q549. What is the use of Amazon Glacier?

Amazon Web Services (AWS)

Ans. Its a storage option provided by AWS which is even cheaper than S3. As the objects are archieved before saving, retrieval time is pretty bad.

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Q550. What is AWS Storage Gateway?

Amazon Web Services (AWS)

Ans. It's an on premise virtual appliance that can be used as cache to store s3 locally at customer site.

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Q551. What are the drawbacks of using Spot EC2 instances ?

Amazon Web Services (AWS)

Ans. You cannot reserve the time slot and they can be made to use whenever they are available.

AWS can Terminate the EC2 instance on their own even if it's in use.

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Q552. What is the use case for AWS Gateway cached , stored and VTL ?

Amazon Web Services (AWS)

Ans. AWS Cached - Low Availability than AWS Stored, Lower cost than AWS Stored

AWS Stored - High Availability, High Local Storage Cost

AWS VTL - S3 Used as Back up only.

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Q553. What are the things to consider while provisioning computing in AWS ?

Amazon Web Services (AWS)

Ans. Service ( EC2, Lambda etc )
AMI ( Operating System and Softwares )
Instance Type ( T,M, R etc )
EBS ( Volume Type , Size )
Price Class ( OnDemand, Dedicated etc )

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Q554. How have you configured Security Groups ?

Amazon Web Services (AWS)

Ans. AWS console >> security groups >> Create security group >> Configure security group bases on Network requirement of EC2 instance

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Q555. What is a Volume Snapshot ?

Amazon Web Services (AWS)

Ans. Snapshots are point in time copies of Volume.

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Q556. Which of the Load balancer - Application / Network provides advanced features ? What is the use of other Load Balancer than if one provides advanced feature than other ?

Amazon Web Services (AWS)

Ans. Application Load Balancer is high level ( Level 7 Networking Layer ) and provides better features and flexibility than Network Load Balancer ( Level 4 Network Layer )

Network Load Balancer is turn provides better performance as it regulates raw traffic.

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Q557. What is the purpose of EC2 Health check ?

Amazon Web Services (AWS)

Ans. We can use this check for variety of things -

1. Monitoring the status / Alarms in case it's down
2. Regulating traffic to healthy instances only through Load Balancer

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Q558. What are the biggest challenges for Java technology in the coming years?

Core Java

Ans. JVM - With Cloud and Serverless, this could be a hurdle for it to be preferred technology.

Confusion between OOP and Functional Programming.

Slower speed of innovation due to wider adoption.

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Q559. Difference between Base Class, Derived Class , Abstract Class and Concrete Class ?

Core Java

Ans. Base Class is a relative term used to signify the Parent class in Parent - Child or Base - derived relationship.

Derived Class is a relative term used to signify the Child class in Parent - Child or Base - derived relationship.

Abstract Class is a class that is not allowed to be instantiated and hence can serve only a base class for it's usage.

Concrete Class is the class which is supposed to be instantiated and hence provide definition for all implementing interface methods and extending abstract methods.

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Q560. Difference between EFS and EBS ?

Amazon Web Services (AWS)

Ans. Both EFS and EBS are block storage but EBS is reserved storage whereas EFS is On Demand.

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