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Q31. What are annotations and what are it's advantages ?

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Q32. Which immutable classes have you worked with ? Can you name some immutable Collections ? How to make an immutable collection ?

Core Java

Ans. string and wrapper class objects

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Q33. If you need to consume messages from the queue faster, which approach will you recommend - batching or concurrency ?

Design

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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Q34. Difference between if and switch ? Can we replace all switch statements with if statements ?

Core Java

Ans. if statement is used to do 2 direction branching whereas switch is used to do multi direction branching in Java.

Yes we can replace all switch statements with nested if statements.

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Q35. Difference between constructor and setter injection ?

Spring

Ans. 1. In Setter Injection, partial injection of dependencies can possible, means if we have 3 dependencies like int, string, long, then its not necessary to inject all values if we use setter injection. If you are not inject it will takes default values for those primitives1. In constructor injection, partial injection of dependencies cannot possible, because for calling constructor we must pass all the arguments right, if not so we may get error

2. Setter Injection will overrides the constructor injection value, provided if we write setter and constructor injection for the same property [i already told regarding this, hope you remember ] But, constructor injection cannot overrides the setter injected values

3. If we have more dependencies for example 15 to 20 are there in our bean class then, in this case setter injection is not recommended as we need to write almost 20 setters right, bean length will increase. In this case, Constructor injection is highly recommended, as we can inject all the dependencies with in 3 to 4 lines [i mean, by calling one constructor]

4. Setter injection makes bean class object as mutable [We can change ] .Constructor injection makes bean class object as immutable [We cannot change ]

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Q36. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs

Core Java

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protection
4. Polymorphism for flexibility and interfacing

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Q37. What is AWS CloudWatch ?

Amazon Web Services (AWS)

Ans. Amazon CloudWatch is a monitoring service for AWS cloud resources like Beanstalk and DB instances. We can use CloudWatch to monitor the state of resources, collect metrices, set alarms and appropriate response to the alarm state.

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Q38. How do you check logs for your application in AWS ?

Amazon Web Services (AWS)

Ans. We can do it by either going to Elastic Beanstalk -> Respective instance -> Logs

or using CloudWatch -> Logs -> Respective Log Group

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Q39. What is Amazon EC2 ?

Amazon Web Services (AWS)

Ans. Amazon Elastic Compute Cloud or EC2 provides scalable computing capacity in the AWS cloud. It can be used to create Virtual Environments , storage and configure. EC2 enables to upgrade or downgrade infrastructure according to the rules defined ( with fluctuation in latency, traffic etc )

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Q40. What is dynamic dispatch in Java ?

Core Java

Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime.

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Q41. Given a string and index for the opening bracket, find the index of matching closing bracket.

Core Java

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Q42. What is the difference between CountingSemaphore and a CountDownLatch?

Operating System

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Q43. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Core Java

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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Q44. How do threads share information ?

Core Java

Ans. Through common memory area.

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Q45. Design a Passport Office system

Design

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Frequently asked Spring interview question.

Q46. What are the components of Spring framework ?

Spring

Ans. Core: [Core, Bean, Context, Expression Language]

Web: [Web, Portlet, Servlet, etc]

Data Access [JMS, JDBC, etc]

AOP, Aspect

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Q47. Write a method / program that will determine if the parenthesis are balanced in a given string.

Core Java

Ans. https://www.geeksforgeeks.org/check-for-balanced-parentheses-in-an-expression/

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Q48. What is a Webdriver ?

Testing

Ans. Selenium WebDriver is a tool for automating web application testing.It helps in replicating the manual tester behavior like keyboard entry, mouse events etc and then matching the output against the expected.

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Q49. What is the difference between authentication and authorization ?

Authentication

Ans. Authentication is the process of verifying the identity and credentials of the user to authenticate him into the system.

whereas

Authorization is the process by which access to a segment , method or resource is determined.

Authorization is usually a step next to authentication.

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Usually asked to entry level software developers.

Q50. Write a program to swap two variables without using third

Core Java

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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Q51. Scale yourself on Java on the scale of 1 to 10

General

Ans. [Open Ended Answer]

The objective of the question is to check how efficient one is in the language so that appropriate level questions are asked. Don't tell too high number if you are being interviewed for a junior or mid level position as the interviewer may throw advance level questions.

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Q52. What is an exception and exception handling in Java ?

Core Java

Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected.

Exception handling is the mechanism which is used to handle such situations.

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Q53. What is the difference between ServletConfig and ServletContext ?

Java EE

Ans. http://www.java4s.com/java-servlet-tutorials/difference-between-servletconfig-and-servletcontext-in-java/

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Q54. What is the difference between following code segments

1.

try {
for(int i=0;i<100;i++){
calculate(i);
}
} catch (Exception ex) {
System.out.println("Error while processing")
}

and

2.

for(int i=0;i<100;i++){
try {
calculate(i);
} catch (Exception ex) {
System.out.println("Error while processing")
}
}

Core Java

Ans. In first case the whole loop will terminate as soon as any exception happens in the method calculate ( assuming calculate method is not handling its exception and those are thrown back at the calling method )

In Second case exception will be caught for individual iteration and hence it wont break the loop and will continue for the next iteration.

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Q55. Difference between Array and ArrayList ?

Core Java

Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a>

Sample Code for ArrayList

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Q56. What is a web service ?

Java EE

Ans. A Web service is a service offered by one system to another, for communication over web through http. XML are JSON are usually used for sending across information from one system to another.

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Frequently asked in high end product companies. Frequently asked in Deloitte.

Q57. How is Hashmap internally implemented in Java ?

Core Java

Ans. https://medium.com/javarevisited/internal-working-of-hashmap-in-java-97aeac3c7beb#:~:text=HashMap%20internally%20uses%20HashTable%20implementation,the%20entries%20into%20the%20map.

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Very Frequently asked to Senior Software Engineers or Developers.

Q58. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Q59. Write a Program to check if 2 strings are Anagrams ?

Core Java

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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Basic and Very Frequently asked.

Q60. What is Polymorphism in Java ?

Core Java

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

Sample Code for overloading

Sample Code for overriding

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