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Q31. What things you would care about to improve the performance of Application if its identified that its DB communication that needs to be improved ?

Solution

Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements )

2. Restructuring Indexes.

3. DB Caching Tuning ( if using ORM )

4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM )

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Q32. What are the factors on which price classes are based on in case of EC2, S3, CloudFront and EBS ?

Amazon Web Services (AWS)

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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Frequently asked to fresh graduates and less experienced.

Q33. Which of the following is tightly bound ? Inheritance or Composition ?

Core Java

Ans. Inheritance.

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Very frequently asked in phone and walk in interviews.

Q34. What are Marker Interfaces ? Name few Java marker interfaces ?

Core Java

Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote

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Q35. Difference between Builder and Composite ?

Ans. Builder is a creational Design Pattern whereas Composite is a structural design pattern. Composite creates Parent - Child relations between your objects while Builder is used to create group of objects of predefined types.

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Q36. What is reflection ?

Ans. It is the process of examining / modifying the behaviour of an object at runtime.

Sample Code for reflection

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Q37. Can we call the garbage collector explicitly ?

Core Java

Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.

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Q38. How Java provide high Performance ?

Core Java

Ans. Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program that turns Java bytecode into instructions that can be sent directly to the processor.

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Q39. What is comparator interface used for ?

Core Java

Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.

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Q40. Can we override compareTo method for Enumerations ?

Core Java

Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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Q41. Difference between jar , war and ear ?

Java EE

Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

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Q42. What is a BlockingQueue?

Data Structures

Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

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This question can be asked in different variants like performace improvement of an application, improving performance for DB communication etc.

Q43. What are the ways in which execution time of the code can be improved ?

Solution

Ans. This depends on entirely upon the code type. For example

1.If its just logic, we can try it to short circuit or put the if / switch case with maximum probability in the beginning.

2. Can use faster data structures, for eg - random retrieval instead of sequence / iterator

3. Working with primitive types or even bytes instead of Objects, even though it may result in marginal improvement.

4. If its service call, then service call with bulk load can help

5. If DB Operation, then with use of Indices , Views or using ORM , cache etc.

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Q44. Write a Program to reverse a Linked List ?

Data Structure

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

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Q45. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.

Core Java

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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Q46. What does import java.util.* means in java ?

Core 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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Q47. 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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Q48. 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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Q49. 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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Q50. 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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Q51. 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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Q52. 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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Q53. What are the different price options available for EC2 ?

Amazon Web Services (AWS)

Ans. On Demand
Reserved
Spot
Dedicated Host

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Q54. 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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Q55. 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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Q56. Can a EC2 instance have multiple Security Groups ? Can a single security group be assigned to multiple Ec2 instances ? If either of them is true , doesn't it result in conflict ?

Amazon Web Services (AWS)

Ans. We can assign multiple security groups to single instance and we can use single security group with multiple instances.

It never results in conflict as security groups only have allow rules and no deny rules. Multiple security groups for an instance results in union of all rules.

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Q57. What is JSON ?

Json

Ans. JSON is "JavaScript Object Notation", primarily used for client-server or server-server communication. Its a much lighter and readable alternative to XML. JSON is language independent and is easily parse-able in all programming languages.

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Q58. Can I import same package/class twice? Will the JVM load the package twice at runtime?

Core Java

Ans. One can import the same package or same class multiple times. Neither compiler nor JVM complains wil complain about it. And the JVM will internally load the class only once no matter how many times you import the same class.

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Q59. What is "Import" used for ?

Core Java

Ans. Enables the programmer to abbreviate the names of classes defined in a package.

Sample Code for import

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Q60. What is a Static import ?

Core Java

Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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