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Q391. Which collection stores element in insertion order ?

Core Java

Ans. LinkedList maintains the insertion order in collection.

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Q392. What are the reasons to choose between reserved and on demand instances ?

Server

Ans. In terms of compute options and configurations, Reserved Instances and On Demand instances are the same. The only difference between the two is that a Reserved Instance is one you rent (reserved) for a fixed duration, and in return you receive a discount on the base price of an On Demand instance.

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Q393. Can you explain the integration between API Gateway and Lambda if we wish to develop services using these tools.

Amazon Web Services (AWS)

Ans. We can create API gateway and give the name of lambda function in order to be linked with lambda function, deploy the API and whenever request will be made from API it will directly be linked to lambda function to perform further process.

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Q394. Can we have a private default method ?

Core Java

Ans. No. The whole idea of default method is to provide a default definition in case the implementing class intend to provide definition for only some of the methods. Making any of the interface method private would restrict it from being implemented by the implementing class. So default method is an option to provide implementation and not restricting a new definition.

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Q395. Find Fibonacci first n numbers using recursion ?

Core Java

Ans. public int fibonacci(int n) {
if(n == 0)
return 0;
else
if(n == 1)
return 1;
else
return fibonacci(n - 1) fibonacci(n - 2);
}

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Q396. Have you ever faced problems with rounding decimal places and what were the reasons ?

Core Java

Ans. 1. The problem with double (x*100)/100 doesn't return exact x but few fractions lesser than x and then if you are using floor rounding , it makes a big difference

2. Rounding only after getting a result vs rounding each outcome of 2 operand make difference

3. Usage of inappropriate Rounding mode and Rounding scale.

4. Results with double and BigDecimal

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Q397. Write code to redo and undo without using system functions ?

Design

^{This question was recently asked at 'Aloha Technologies'.This question is still unanswered. Can you please provide an answer.}

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Q398. What development process / methodology are you using ? Are you using agile ?

General

^{This question was recently asked at 'Spillman Technologies'.This question is still unanswered. Can you please provide an answer.}

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Q399. Difference between == and === ?

JavaScript

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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Q400. Can we have multiple inheritance in java using abstract class ?

Core Java

Ans. No

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Q401. Describe structure of a Web application.

architecture

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Q402. 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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Q403. 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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Q404. 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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Q405. 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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Q406. 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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Q407. 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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Q408. 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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Q409. 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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Q410. 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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Q411. Difference between StoreModule.forRoot() and StoreModule.forFeature() ?

NgRx

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

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Q412. 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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Q413. How to avoid cloning, serialization in the singleton class ?

Design

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

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Q414. 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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Q415. 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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Q416. 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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Q417. What is a Volume Snapshot ?

Amazon Web Services (AWS)

Ans. Snapshots are point in time copies of Volume.

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Q418. 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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Q419. 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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Q420. 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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