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Q121. Who invokes a thread's run method ?

Ans. After a thread is started using a call to start method, JVM invokes the thread’s run method when the thread is initially executed.

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Q122. How and Why Strings are interned in Java ?

Core Java

Ans. String class has a public method intern() that returns a canonical representation for the string object. String class privately maintains a pool of strings, where String literals are automatically interned.

these are automatically interned so as to have efficient String comparison using == operator instead of equals which is usually slower.

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Q123. What are the different primitive data types in Java ?

Core Java

Ans. boolean
byte
char
double
float
int
long
short
void

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Q124. Write a Program to print duplicate words in a String

Core Java

Ans. public class BuggyBread {
public static void main(String args[]) {
String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
Set<String> words = new HashSet();
for(String word:str.split(" ")){
if(words.contains(word)){
System.out.println(word);
} else {
words.add(word);
}
}
}
}

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Q125. Write code to find second largest number in an array of integers.

Core Java

Ans. int arr[]={1,3,5,6,4,8,9,2,10};
Arrays.sort();
System.out.println(arr[arr.length-1]);

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Frequently asked Spring interview question.

Q126. 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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Q127. Is synchronized a keyword , modifier, identifier? what is it ?

Core Java

Ans. synchronized is a keyword and a modifier. The synchronized keyword is used to indicate that a method can be accessed exclusively by one thread at a time.

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Q128. 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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Q129. 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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Q130. How to calculate lcm of two numbers ?

Core Java

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

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Q131. Explain Generics in Java ?

Core Java

Ans. Generics are a facility of generic programming that were added to the Java programming language in 2004 within J2SE5.0. They allow "a type or method to operate on objects of various types while providing compile-time type safety.

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Q132. 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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Q133. What is the difference between SDLC and Agile ?

Process

Ans. Here are the differences between Agile and Waterfall Methodology:

The software development process is divided into different phases in the Waterfall model while Agile methodology segregates the project development lifecycle into sprints

Waterfall is a structured software development methodology, and often times can be quite rigid, whereas the Agile methodology is known for its flexibility

According to the Waterfall model, software development is to be completed as one single project, which is then divided into different phases, with each phase appearing only once during the SDLC. However, the Agile methodology can be considered as a collection of many different projects, which are nothing but the iterations of the different phases focusing on improving the overall software quality with feedback from users or the QA team

If you want to use the Waterfall model for software development, then you have to be clear with all the development requirements beforehand as there is no scope of changing the requirements once the project development starts. The Agile methodology, on the other hand, is quite flexible, and allows for changes to be made in the project development requirements even after the initial planning has been completed

All the project development phases such as designing, development, testing, etc. are completed once in the Waterfall model while as part of the Agile methodology, they follow an iterative development approach.

As a result, planning, development, prototyping and other software development phases can appear more than once during the entire SDLC One of the major differences between Agile and Waterfall development methodology is their individual approach towards quality and testing.

In the Waterfall model, the Testing phase comes after the Build phase, but, in the Agile methodology, testing is typically performed concurrently with programming or at least in the same iteration as programming

While Waterfall methodology is an internal process and does not require the participation of customers, the Agile software development approach focuses on customer satisfaction and thus, involves the participation of customers throughout the development phase

The Waterfall model can be regarded as a stringently sequential process, however, the Agile methodology is a highly collaborative software development process, thereby leading to better team input and faster problem solving

The Waterfall model is best suited for projects which have clearly defined requirements and in which change is not expected at all, while Agile development supports a process in which the requirements are expected to change and evolve. Thus, if you are planning to develop a software that would require frequent overhauls and has to keep up with the technology landscape and customer requirements, Agile is the best approach to follow

The Waterfall model exhibits a project mindset and lays its focus strictly on the completion of project development, while Agile introduces a product mindset that focuses on ensuring that the developed product satisfies its end customers, and changes itself as the requisites of customers change

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Q134. Explain OOps concepts.

Core Java

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Frequently asked in Genpact.

Q135. What is object cloning ?

Core Java

Ans. Its is the process of creating exact copy of an object being cloned. In Object class one native method called clone() is there which is meant for Shallow Cloning of Object. Shallow cloning means bitwise copy of an object.In case of primitive data type it will create an exact copy of primitive values as well as variables but if the object contains any reference of an object then it will not copy the referenced object rather it will create the copy of reference variable and assigned it to the old object.

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Q136. What is collection framework in Java ?

Core Java

Ans. The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures. Although referred to as a framework, it works in a manner of a library. The JCF provides both interfaces that define various collections and classes that implement them.

Sample Code for Map

Sample Code for HashMap

Sample Code for Treemap

Sample Code for set

Sample Code for hashset

Sample Code for treeset

Sample Code for list

Sample Code for arraylist

Sample Code for linkedlist

Sample Code for queue

Sample Code for priorityqueue

Sample Code for concurrenthashmap

Sample Code for vector

Sample Code for stack

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Q137. What is your role in current project ?

General

Ans. Possible Answer - Java Developer

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Q138. Why do you want to leave your current job ?

General

Ans. The most effective and acceptable reasons for leaving your current job should be positive e.g. moving forward in your life or career

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Q139. Do you like your work in current project ?

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

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Q140. What is garbage collection ?

Core Java

Ans. The garbage collection is a facility wherein a program runs on the Java Virtual Machine which gets rid of objects, which are not being used by a Java application anymore. It is a form of automatic memory management and recollection.

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Q141. What methodology and technology stack do you use ?

General

Ans. [Open Ended Answer]

Possible Answer - We are using Agile. We have daily standups, Bi weekly Backlog Grooming , Planning and Retrospective, We have a 2 week sprint and We use Jira for Scrum Management. We are using Java 8, Spring Boot, JSF , Apache Kafka , Soap as well as Rest Services.

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Q142. Sort a List of Objects using comparable and comparator

Core Java

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Q143. What is setter injection ?

Spring

Ans. Setter Injection in Spring is a type of dependency injection in which the framework injects the dependent objects into the client using a setter method.

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Q144. What is the difference between TreeSet and TreeMap ?

Core Java

Ans. TreeSet contains only values as elements whereas TreeMap contains Key value pairs.

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Q145. Write code to sort an array.

Algorithm

Ans. https://www.geeksforgeeks.org/arrays-sort-in-java-with-examples/

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Q146. 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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Q147. Have you worked on Linux Systems ?

General

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

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Q148. What sets you apart from other developers ?

or

What are the distinguished qualities you have ?

General

Ans. https://blog.timesunion.com/careers/the-10-most-important-personality-traits-for-career-success/633/

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Q149. What is TypeCasting ?

Core Java

Ans. Assigning a value of one type to a variable of another type is known as Type Casting.

Example :

int x = 10;
byte y = (byte)x;

In Java, type casting is classified into two types, Widening Casting(Implicit) widening-type-conversion and Narrowing Casting (Explicitly done) narrowing-type-conversion.

Widening or Automatic type converion - Automatic Type casting take place when,the two types are compatible and the target type is larger than the source type

Example :

public class Test {
public static void main(String[] args) {
int i = 100;
long l = i; //no explicit type casting required
float f = l;//no explicit type casting required
System.out.println("Int value " i);
System.out.println("Long value " l);
System.out.println("Float value " f);
}
}

Narrowing or Explicit type conversion - When you are assigning a larger type value to a variable of smaller type, then you need to perform explicit type casting.

Example :

public class Test{
public static void main(String[] args) {
double d = 100.04;
long l = (long)d; //explicit type casting required
int i = (int)l;//explicit type casting required
System.out.println("Double value " d);
System.out.println("Long value " l);
System.out.println("Int value " i);
}
}

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Q150. Tell me about thread pool?

Design

Ans. Java provides its own implementations of the thread pool pattern, through objects called executors. These can be used through executor interfaces or directly through thread pool implementations which does allow for finer-grained control. The java.util.concurrent package contains the following interfaces:

Executor : a simple interface for executing tasks.ExecutorService a more complex interface which contains additional methods for managing the tasks and the executor itself.

ScheduledExecutorService: extends ExecutorService with methods for scheduling the execution of a task.Alongside these interfaces, the package also provides the Executors helper class for obtaining executor instances, as well as implementations for these interfaces.

Generally, a Java thread pool is composed of:

The pool of worker threads, responsible for managing the threads.
A thread factory that is responsible for creating new threads.
A queue of tasks waiting to be executed.

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