Frequently asked Interview Questions and Answers

Interview Questions and Answers - Order By Newest

Frequently asked.

Q131. When does the finally block gets executed ?

Ans. A finally block of code always executes, whether or not an exception has occurred.The only time finally won't be called is if you call System.exit() or if the JVM crashes first.

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Q132. Explain System.out.println ?

Core Java

Ans. System is a class within java.lang package that contains several useful class fields and methods. It cannot be instantiated and hence can use only statically.even in this case this has been used statically i.e with class name itself and without creating an instance.

out is the static reference of Printstream declared as following in the System Class -

public final static PrintStream out = null;

println is the method of PrintStream class.

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Very Frequently asked to Senior Software Engineers or Developers.

Q133. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Q134. What is database Normalization ?

Database

Ans. https://en.wikipedia.org/wiki/Database_normalization

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Q135. What is the use of static keyword in Java ?

Core Java

Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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Q136. Explain various Searching and Sorting Algorithms ?

Algorithm

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

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Q137. What is a Servlet Filter ?

Java EE

Ans. It's an object that can intercept http request and response and hence we can take appropriate action on those requests.

There are different types of filters based on Specifications like

Authentication
Logging
Encryption
Tokenizing

etc

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Q138. 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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Q139. Describe structure of a Web application.

architecture

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Q140. 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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Q141. Between Encrypted Password authentication and IP Authentication , which one would you prefer and why ?

Authentication

Ans. IP authentication is very restrictive, if IP changes for some reason then getting the new IP white listed on the server firewall could run your day pretty long. I would prefer encrypted password authentication cause it is not affected by IP changes and not limited to a white listed IP, I could use any different machine and get through authentication without any hassle.

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Q142. 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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Q143. What is a cookie ?

Java EE

Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification.

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Q144. Can static method access instance variables ?

Core Java

Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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Very frequently asked. Usually asked in this format or as difference with interfaces / concrete classes.

Q145. What is an abstract class ?

Core Java

Ans. Abstract class is the class that is not supposed to be instantiated. The purpose of the class to only have extension to the derived class.

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Frequently asked.

Q146. What is an Iterator?

Core Java

Ans. Iterator is an interface that provides methods to iterate over any Collection.

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Q147. Which interface provides the capability to store objects using a key-value pair?

Core Java

Ans. java.util.map

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Frequently asked to fresh graduates.

Q148. What are the difference between Threads and Processes ?

Operating System

Ans. 1. when an OS wants to start running program it creates new process means a process is a program that is currently executing and every process has at least one thread running within it.
2). A thread is a path of code execution in the program, which has its own local variables, program counter(pointer to current execution being executed) and lifetime.
3. When the JavaVirtual Machine (JavaVM, or just VM) is started by the operating system, a new process is created. Within that process, many threads can be created.
4. Consider an example : when you open Microsoft word in your OS and you check your task manger then you can see this running program as a process. now when you write something in opened word document, then it performs more than one work at same time like it checks for the correct spelling, it formats the word you enter , so within that process ( word) , due to different path execution(thread) all different works are done at same time.
5. Within a process , every thread has independent path of execution but there may be situation where two threads can interfere with each other then concurrency and deadlock come is picture.
6. like two process can communicate ( ex:u open an word document and file explorer and on word document you drag and drop another another file from file explorer), same way two threads can also communicate with each other and communication with two threads is relatively low.
7. Every thread in java is created and controlled by unique object of java.lang.Thread class.
8. prior to jdk 1.5, there were lack in support of asynchronous programming in java, so in that case it was considered that thread makes the runtime environment asynchronous and allow different task to perform concurrently.

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Q149. Why java doesn't support multiple Inheritence ?

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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Frequently asked to fresh graduates.

Q150. What is the difference between yield() and sleep()?

Operating System

Ans. When a object invokes yield() it returns to ready state. But when an object invokes sleep() method enters to not ready state.

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Usually asked only to fresh graduates.

Q151. What is the initial state of a thread when it is created and started?

Ans. Ready state.

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Q152. What restrictions are placed on method overriding?

Ans. Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.

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Q153. How does a try statement determine which catch clause should be used to handle an exception?

Core Java

Ans. When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.

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Q154. Explain static blocks in Java ?

Core Java

Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:

static {
// whatever code is needed for initialization goes here
}

A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

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Q155. Explain Annotations ?

Ans. Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate. Annotations have a number of uses, among them:
â€¢ Information for the compiler â€” Annotations can be used by the compiler to detect errors or suppress warnings.
â€¢ Compile-time and deployment-time processing â€” Software tools can process annotation information to generate code, XML files, and so forth.
â€¢ Runtime processing â€” Some annotations are available to be examined at runtime.

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Q156. What is a finalize method ?

Core Java

Ans. finalize() method is called just before an object is destroyed.

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Recently asked in Infoview Technologies.

Q157. What is a Default Constructor ?

Core Java

Ans. The no argument constructor provided by Java Compiler if no constructor is specified.

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Q158. Whats the purpose of marker interfaces ?

Ans. They just tell the compiler that the objects of the classes implementing the interfaces with no defined methods need to be treated differently.

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Usually asked only to fresh graduates and less experienced developers.

Q159. What is a daemon thread? Give an Example ?

Ans. These are threads that normally run at a low priority and provide a basic service to a program or programs when activity on a machine is reduced. garbage collector thread is daemon thread.

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Very Frequently asked Spring question.

Q160. What is bean auto wiring?

Spring

Ans. The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory without using and elements.

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