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Interview Questions and Answers for 'Amazon' - 300 question(s) found - Order By Newest

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Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews.
  Q1. What are the difference between composition and inheritance in Java?Core Java
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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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Very frequently asked to Fresh graduates.
  Q2. What is the difference between Encapsulation and Abstraction?Core Java
Anonymous
Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level

2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.

3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.

4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q3. What is the difference between ArrayList and LinkedList ?Core Java
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Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

  Sample Code for ArrayList

  Sample Code for LinkedList

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q4. Differences between abstract class and interface ?Core Java
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Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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   Like         Discuss         Correct / Improve     java   classes   abstract class   interfaces     Asked in 81 Companies      basic        frequent


Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback)
  Q5. Describe, in general, how java's garbage collector works ?Core Java
Anonymous
Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected.

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 Q6. Design an e commerce application using AWS ? What AWS services will you use ?Amazon Web Services (AWS)2019-01-08 16:24:47

Ans. CloudFront for Static Media and cached content
EC2 and EKS ( Docker ) for main application computing
RDS and DynamoDB for Database
Lambda ( computing ) for running back end cron jobs
Kinesis for streaming and SQS for queuing
CloudWatch for Monitoring
CloudFormation for Infrastructure templating
S3 for Object Storage

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 Q7. Difference between AWS Cloud Formation and AWS AMI ?Amazon Web Services (AWS)2019-01-11 13:40:03

Ans. AMI is an Amazon Machine Image. It contains the configuration to enable to boot up an EC2 instance with said configuration whereas Cloud formation is a templating language that allows to describe how to build a VPC and also allows you to create AWS services

AMI is templating specific to instances whereas the scope of CloudFormation templating is much bigger. CloudFormation could use AMI for launching instances along with other services.

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 Q8. Difference between Region , Availability zone and Edge Locations ?Amazon Web Services (AWS)2019-01-14 10:57:57

Ans. A Region is a Geographical entity like US-East , US-West etc. Each Region may have multiple availability zones where each zone comprise of 1 or more Data Center located with each other.

Edge Locations are the sites that hosts cached content for faster delivery and for saving network traffic as they feed content from sites that are local or near to consumption.

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 Q9. What are the different S3 storage Tiers ?Amazon Web Services (AWS)2019-01-14 14:16:05

Ans. S3 Standard
S3 IA - Infrequently Accessed
S3 One Zone IA - One Zone only , Infrequently Accessed
S3 Glacier - achieved

S3 Standard is most expensive , Glacier is least expensive

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 Q10. What are the factors on which customers are charged for using S3 ?Amazon Web Services (AWS)2019-01-14 14:51:36

Ans. Storage Tier ( IA , Standard , Glacier etc )
Storage ( Volume of Data )
No of Requests
Meta Data
Data Transfer Speed acceleration through cache and Edge Location

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 Q11. What are the factors on which price classes are based on in case of EC2, S3, CloudFront and EBS ?Amazon Web Services (AWS)2019-01-16 13:22:38

Ans. EC2 - Time and Reservation , Instance Type ( Memory , Computation power )
S3 - Accessibility Frequency , Data Transfer , Storage Space
CloudFront - Geography, No of Locations
EBS - IOPS, Access Frequency

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 Q12. What the difference between S3 and EFS ?Amazon Web Services (AWS)2019-01-27 12:50:40

Ans. EFS is file storage whereas S3 is object storage.

EFS is filesystem presented over IP network as normal OS drive, while S3 is HTTP accessed store.

EFS is capable of being mounted whereas S3 doesn't.

S3 has capabilities beyond just filesystem, there is whole metadata part where you can store info about your objects in S3.

As S3 is accessed over http , it's capable of hosting a static web site on it's own whereas EFS needs a computing and frontend service to have such capability.

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 Q13. What is the relationship between VPC and subnet ? Can you tell with an example ?Networking2019-01-27 21:19:19

Ans. A VPC is devided into multiple subnets. Subnet in a particular VPC could be public or private.

For Example - A particular account may have multiple vpc's for each of the business type. For each Business or VPC , One can have different subnets to cater to each department so that access across departments could be restricted. But still there could be identities that have control over different subnets. Moreover we could have multiple subnets for each department so as to have distinguished public and private networks having different types of applications ( public facing or internal consumption )

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   Like         Discuss         Correct / Improve     aws vpc  aws subnet  subnet  vpc  Amazon Web Services (AWS)


 Q14. What is the difference between single instance Web environment and Load Balanced Auto Scaling ? Amazon Web Services (AWS)2017-06-07 13:20:04

Ans. Single instance means there is only 1 instance that will bear all the traffic load whereas Load balanced server means that there will be a cluster of servers that will host the application and load will be balanced distributed among them. Auto Scaling means that the number of instances will be expanded / shrunken based on the rule. Rule could be the traffic count , response time etc.

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 Q15. What is cloud computing ?Cloud Computing2018-01-11 10:53:46

Ans. Cloud Computing is a way of using IT infrastructure with following traits -

1. On Demand Infrastructure
2. Broad Network Access
3. Resource Pooling
4. Rapid Elasticity
5. Measured Service

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 Q16. What are the services provided by AWS ?Amazon Web Services (AWS)2018-01-11 10:57:06

Ans. AWS provides various types of services like Computing ( EC2 , Lambda , EKS ), Storage ( S3, Glacier ), Database ( RDS , DynamoDB ), Streaming ( Kinesis ), Queue ( SQS ), Security and Access ( IAM ) etc.

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 Q17. What are the problems one could face while working with serverless technologies like AWS Lambda ?Amazon Web Services (AWS)2018-01-30 18:05:47

Ans. Warm up time for certain technologies like Java ( JVM Warmup )

Performance

Size of Deployable ( Bigger size packaging should go in S3 )

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 Q18. What is the cost of using Cloud Formation ?Amazon Web Services (AWS)2019-01-08 15:53:06

Ans. Cloud Formation does not have any additional cost but you are charged for the underlying resources it builds.

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 Q19. How does AWS Lambda handle failure during event processing?Amazon Web Services (AWS)2019-01-08 16:14:00

Ans. In AWS Lambda we can run a function in synchronous or asynchronous mode. In synchronous mode, if AWS Lambda function fails, then it will just give an exception to the calling application. In asynchronous mode, if AWS Lambda function fails then it will retry the same function at least 3 times.If AWS Lambda is running in response to an event in Amazon DynamoDB or Amazon Kinesis, then the event will be retried till the Lambda function succeeds or the data expires. In DynamoDB or Kinesis, AWS maintains data for at least 24 hours.

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 Q20. What does AMI include ?Amazon Web Services (AWS)2019-01-11 13:42:29

Ans. A template for the instance.

Launch permission decisions

A block device mapping, when an instance is launched it determines the volumes to attach to that instances.


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 Q21. Why is cloud infrastructure so powerful ?Cloud Computing2019-01-14 10:52:40

Ans. Because it gives the ability to provision infrastructure on Demand with No contracts and strings attached.

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 Q22. Which region is the latest and most popular in AWS ? What are the advantages and disadvantages of using this region ?Amazon Web Services (AWS)2019-01-14 10:56:40

Ans. US-East Virginia

This is the oldest and most popular region. All new features are rolled first in this region and hence they are first available there. The downside is that because of experimentation with new services, unavailability time is quite high.

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 Q23. What are the advantage of having Edge Locations ?Amazon Web Services (AWS)2019-01-14 11:00:06

Ans. It saves Network traffic and facilitates faster delivery by hosting bulk media and cached data near to client.

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 Q24. What does effect , action and resource means with respect to AWS IAM policy ?Amazon Web Services (AWS)2019-01-14 13:51:23

Ans. effect means whether the effect of this Policy is to allow or deny, action means the type of action ( read , write ) and service, and resource is the resource where this should apply.

For example - If we want to have a Policy of providing read access on S3 ,
effect will be "allow"
action will be "s3:GetObject"
resource will be "arn:aws:s3:::examplebucket/*"

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 Q25. Within AWS S3, Why new files are available immediately for read operation but not the updates ? Amazon Web Services (AWS)2019-01-14 14:08:59

Ans. Because new files will be fed from where ever they are first available but AWS have no way to identify which is the most updated version among the various regions. The updated version can only be assured once the replication to all availability zones is complete.

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 Q26. What kind of Access Policy should be kept on S3 Buckets and Policy ?Amazon Web Services (AWS)2019-01-15 11:49:49

Ans. We should only allow access that's needed. So the security Policy should be as restrictive as possible.

Buckets and Files should never be made public unless until they are needed it to be like that.

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 Q27. How can we protect from accidental deletes in S3 ?Amazon Web Services (AWS)2019-01-15 11:55:33

Ans. Versioning ( will create Delete marker )
MFA Delete ( authentication upon deletion )
Cross Region Replication ( Replicates aren't deleted )

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 Q28. How can we restrict CloudFront access to a particular Geography ?Amazon Web Services (AWS)2019-01-15 12:07:20

Ans. We can select the appropriate Price Class if that suits us.

We can do Geo Targeting by black listing / white listing certain geographies.

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 Q29. What is the use case for "On Demand" EC2 ?Amazon Web Services (AWS)2019-01-16 12:24:45

Ans. If the computation required is Spiky and unpredictable.

If it's first time use.

If the lifespan of the application isn't known.

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 Q30. What is the use case for "Spot" EC2 plan ?Amazon Web Services (AWS)2019-01-16 12:26:33

Ans. If the usage is non continuous and have flexible start and End Time. For ex - Analysis , Research , mining etc.

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