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Q541. 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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Q542. Difference between StoreModule.forRoot() and StoreModule.forFeature() ?

NgRx

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

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Q543. 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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Q544. 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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Q545. How to avoid cloning, serialization in the singleton class ?

Design

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

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Q546. 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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Q547. 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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Q548. 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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Q549. 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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Q550. 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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Q551. 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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Q552. What is a Volume Snapshot ?

Amazon Web Services (AWS)

Ans. Snapshots are point in time copies of Volume.

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Q553. 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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Q554. 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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Q555. 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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Q556. 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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Q557. 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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Q558. Which AWS computing service provides IAAS, PAAS , Containerization and Serverless ?

Amazon Web Services (AWS)

Ans. EC2 is IAAS
Elastic Beanstalk is PAAS
EKS is Containerization service
Lambda is Serverless

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Q559. What are the advantages and disadvantages of using Lambda over EC2 ?

Amazon Web Services (AWS)

Ans. Advantages -

Much Cheaper
Continuous scaling
Higher level and Serverless

Disadvantages -

Warm up time
Limited flexibility in terms of technologies
Limited control

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Q560. Can we associate a single EFS volume with multiple EC2 instances ?

Amazon Web Services (AWS)

Ans. Yes

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Q561. What are the different trigger types in AWS Lambda ?

Amazon Web Services (AWS)

Ans. Api Gateway
Alexa
CloudFront
CloudWatch
Code Commit
Kinesis
S3
SNS

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Q562. Why AWS named the DNS service as Route 53 ?

Amazon Web Services (AWS)

Ans. Route is for routing which is the purpose of DNS and Default port for DNS is 53

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Q563. What happens to backups if we delete the RDS instance ?

Amazon Web Services (AWS)

Ans. Automated Backups are deleted automatically whereas Snapshots are preserved. Upon terminating RDS instance , AWS gives a warning about that and requests to create a final snapshot before terminating the instance.

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Q564. Describe best practices with respect to AWS security groups ?

Amazon Web Services (AWS)

Ans. Configure it while creating EC2 instance only

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Q565. How would you secure EC2, Volume and Snapshots in Cloud ?

Amazon Web Services (AWS)

Ans. Adding more security group, it works like a firewall

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Q566. What is mounting in AWS ?

Amazon Web Services (AWS)

Ans. Attaching Volumes ( EBS / EFS ) on AWS Computing ( EC2, EKS )

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Q567. Can we have internal or private ELB as origin in cloudfront ?

Amazon Web Services (AWS)

Ans. No, it should be public as cloudfront doesn't have a way to access private ELB.

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Q568. Difference between NAT Instances and NAT Gateway

Amazon Web Services (AWS)

Ans. High bandwidth and availability in NAT Gateway
NAT Gateway is completely managed by AWS
NAT Gateway is auto scalable
NAT Instance is just like EC2 instance and hence backed by security group
NAT Instance can be used as bastion host whereas NAT Gateway cannot be.

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Q569. When singleton can break and how to resolve it

Design

Ans. Deserialization. In serialization, we can save the object of a byte stream into a file or send over a network. Suppose if you serialize the Singleton class, and then again de-serialize that object, it will create a new instance, hence deserialization will break the Singleton pattern.

To overcome this issue, we need to override readResolve() method in the Singleton class and return the same Singleton instance.

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Q570. why string pool concept for only String but not for StringBuffer ?

Core Java

Ans. As String is immutable so by maintaining pool area we can refer the object to same area if they are with same content. But when it comes to string buffer or builder then due to mutable property if we do so then all the objects referring to that area will from now has new content.. So as to avoid this pool is present only in string.

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