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Usually asked to entry level software developers.

Q221. Write a program to swap two variables without using third

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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_{Like Discuss Correct / Improve code coding Asked in 37 Companies basic frequent}

Q222. What are the disadvantages of Hibernate over native APIs ?

^{This question is still unanswered. Can you please provide an answer.}

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Q223. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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_{Like Discuss Correct / Improve abstract class interfaces Asked in 2 Companies Basic}

Q224. Can we overload method as following ?

void method(int... x){};
void method(int[] x){};

Ans. No. Because java internally treats var args as arrays and hence both method declarations will generate the same byte code and hence would result in ambiguity while determining call binding.

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Q225. What is the difference between single instance Web environment and Load Balanced Auto Scaling ?

Amazon Web Services (AWS)

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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Q226. What does import java.util.* means in java ?

Ans. It means import all the classes and interfaces within java.util package and make them available to use within the current class or interface. This is shorthand wild card annotation for importing all classes within a particular package. This won't import the classes within the sub packages of java.util.

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Q227. What are the benefits of Dependency Injection or IOC ?

Ans. Central place for configuring dependencies.

No need to create object, container manage all this By using Run time polymorphism and association.

Facilities development of framework / libraries by injecting implementation classes in the implementation code.

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Q228. If you need to consume messages from the queue faster, which approach will you recommend - batching or concurrency ?

Ans. Each has it's own advantages

Batching requires less resources but may result in loosing whole batch in case of failure whereas concurrency even though is little more expensive in terms of resources but would result in minimal loss in case of failure.

In case messages are to be consumed in a particular order, batching them in that order and then consuming them makes better sense.

if incoming messages are not continuous , it makes more sense to do concurrency as we need not wait for all messages to form a batch and flush. Though time sensitivity can be added but that would add unnecessary complexity.

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Q229. What is the difference between Singleton and Prototype Bean scope in Spring ?

Ans. Prototype scope - A new object is created each time it is injected/looked up. It will use new SomeClass() each time.

Singleton scope - It is the default scope. The same object is returned each time it is injected/looked up. Here it will instantiate one instance of SomeClass and then return it each time.

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Q230. What is the use of Object class ?

Ans. 1. Default definition for some of the methods , like equals, hashcode etc that gets carried to all objects even if you don't define anything. But that default definition is kind of like assigning 0 to integer, it just provide a safe state , nothing much for comparison.

2. Places where you have no idea about what object you may receive and just want to perform out of 8 basic methods of object class, something like printing their string representation ( defined by their toString method ), or equality ( using their equals method )

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Q231. What is cloud computing ?

Cloud Computing

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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Q232. What are the problems one could face while working with serverless technologies like AWS Lambda ?

Amazon Web Services (AWS)

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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Q233. What is the difference between subject and observable ?

Ans. Subject has state, it keeps a list of observers. On the other hand, an Observable is really just a function that sets up observation. While Subjects are Observables, Subjects also implement an Observer interface.

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Q234. What are the disadvantages of Design Patterns ?

Ans. 1. Design patterns are abstraction heavy and hence sometimes creates memory and performance overheads.

2. Sometimes they create unnecessary complexity without much added advantage.

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Q235. Differences between class not found exception and noclassdef found error ?

Ans. ClassNotFoundException is an exception that occurs when we try to load a class at run time using Class.forName() or loadClass() methods and mentioned classes are not found in the classpath.

NoClassDefFoundError is an error that occurs when a particular class is present at compile time, but was missing at run time.

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Q236. serialization and deserialization of singleton class

Ans. The problem with serialized singleton class is that whenever we deserialize it, it will create a new instance of the class. To overcome this scenario all we need to do is to provide the implementation of readResolve() method.

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Q237. What is the cost of using Cloud Formation ?

Amazon Web Services (AWS)

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

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Q238. How does AWS Lambda handle failure during event processing?

Amazon Web Services (AWS)

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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Q239. Why is cloud infrastructure so powerful ?

Cloud Computing

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

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_{Like Discuss Correct / Improve Amazon Web Service (AWS) Google Cloud Platform (GCP)}

Q240. Which region is the latest and most popular in AWS ? What are the advantages and disadvantages of using this region ?

Amazon Web Services (AWS)

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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Q241. What are the advantage of having Edge Locations ?

Amazon Web Services (AWS)

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

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Q242. Within AWS S3, Why new files are available immediately for read operation but not the updates ?

Amazon Web Services (AWS)

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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Q243. What kind of Access Policy should be kept on S3 Buckets and Policy ?

Amazon Web Services (AWS)

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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Q244. How can we protect from accidental deletes in S3 ?

Amazon Web Services (AWS)

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

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Q245. How can we restrict CloudFront access to a particular Geography ?

Amazon Web Services (AWS)

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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Q246. What is the use case for "On Demand" EC2 ?

Amazon Web Services (AWS)

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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Q247. What is the use case for "Spot" EC2 plan ?

Amazon Web Services (AWS)

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

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Q248. What are the different price options available for EC2 ?

Amazon Web Services (AWS)

Ans. On Demand
Reserved
Spot
Dedicated Host

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Q249. What EC2 configuration would you use if you have to use it for Bitcoin mining ?

Amazon Web Services (AWS)

Ans. Keeping Low cost for processing , i would choose

Spot Price Plan
F1 or P3 Instance Type
Cold Hdd (SCI ) EBS Volume

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Q250. Which AWS services would you use if you have find a cheapest solution for an analytics application ?

Amazon Web Services (AWS)

Ans. Computation

Spot Price Plan
F1 or P3 Instance Type
Cold Hdd (SCI ) EBS Volume

Storage

S3-IA

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