30+ NSK Interview Questions and Answers

Keywords for thread safe program in Java

• Synchronization using synchronized keyword

• Using volatile keyword for shared variables

• Using atomic classes for thread safe operations

• Using thread safe collections like ConcurrentHashMap

• Using locks and semaphores for synchronization

• Avoiding shared mutable state

• Using immutable objects

• Using thread local variables

To start Spring Boot app with class error, disable strict classpath checking.

• Add 'spring.main.lazy-initialization=true' to application.properties.

• Disable strict classpath checking by adding 'spring.main.allow-bean-definition-overriding=true'.

• Use 'spring.main.banner-mode=off' to disable banner.

• Use 'spring.main.web-environment=false' to disable web environment.

• Use 'spring.main.headless=true' to enable headless mode.

JDK is a development kit, JRE is a runtime environment, and JVM is a virtual machine for running Java programs.

• JDK (Java Development Kit) is a software development kit used for developing Java applications. It includes JRE, compiler, debugger, and other tools.

• JRE (Java Runtime Environment) is a software package that provides the libraries, Java Virtual Machine (JVM), and other components necessary for running Java applications.

• JVM (Java Virtual Machine) is an abstract machine...read more

Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs.

• JVM is an abstract machine that provides a runtime environment for Java bytecode to be executed.

• It is responsible for converting Java bytecode into machine code that can be understood by the computer's operating system.

• JVM is platform-independent, allowing Java programs to run on any device or operating system that has a JVM implementation.

• It manages memory, handles garbage collection...read more

Class modification exception occurs when a class is modified after it has been loaded by the JVM.

• This exception is thrown when a class is modified and then reloaded by the JVM.

• It can occur when a class is modified during runtime or when a new version of a class is loaded.

• This exception can be avoided by using a class loader that isolates the classes from each other.

• An example of this exception is when a method is added to a class and then the class is reloaded by the JVM.

RequestBody annotation is used to bind the HTTP request body to a method parameter in Spring.

• Used in Spring MVC to handle POST requests

• Used to map the request body to a Java object

• Can be used with other annotations like @PostMapping

• Can be used to validate the request body using @Valid annotation

James Gosling is considered the father of Java programming language.

• James Gosling, a Canadian computer scientist, is credited with creating the Java programming language in the early 1990s.

• He developed Java while working at Sun Microsystems, now owned by Oracle.

• Java was officially released by Sun Microsystems in 1995 and has since become one of the most popular programming languages in the world.

JIT compiler stands for Just-In-Time compiler, which compiles Java bytecode into native machine code at runtime for improved performance.

• JIT compiler is part of the Java Virtual Machine (JVM) and helps in optimizing the performance of Java applications.

• It compiles Java bytecode into native machine code on-the-fly, right before executing it.

• JIT compiler identifies hot spots in the code (frequently executed portions) and optimizes them for better performance.

• Examples of JIT com...read more

Method overriding in Java allows a subclass to provide a specific implementation of a method that is already provided by its superclass.

• Create a subclass that extends a superclass with a method to be overridden

• Define a method in the subclass with the same signature as the superclass method

• Use the @Override annotation to indicate that the method is intended to override a superclass method

• Call the superclass method using the super keyword within the overridden method

To make a class immutable, use final keyword, private fields, no setters, and defensive copying.

• Use final keyword to make class unextendable

• Use private fields to prevent direct access

• No setters to prevent modification

• Defensive copying to prevent modification of mutable objects

• SOLID principles and factory design pattern can be used to create immutable objects

• Example: String class in Java is immutable

Wipro BPS has multiple branches across India and globally.

• Wipro BPS has branches in major cities like Bangalore, Chennai, Mumbai, Pune, Hyderabad, etc.

• They also have branches in countries like the USA, UK, Australia, etc.

• The exact branch location for a Java Developer role may depend on the project and client requirements.

Java and JavaScript are two different programming languages with different use cases.

• Java is used for building server-side applications, Android apps, and enterprise software.

• JavaScript is used for building interactive web applications and front-end development.

• Java is a compiled language while JavaScript is an interpreted language.

• Java is statically typed while JavaScript is dynamically typed.

• Java code runs on the Java Virtual Machine (JVM) while JavaScript code runs on web ...read more

Method overriding is a way to provide a specific implementation of a method in a subclass that is already provided by its superclass.

• Method overriding allows a subclass to provide a specific implementation of a method that is already defined in its superclass.

• The method in the subclass must have the same name, return type, and parameters as the method in the superclass to override it.

• Method overriding is used to achieve runtime polymorphism in Java.

• Example: class Animal { voi...read more

JavaScript and C++ are programming languages used for web development and system programming respectively.

• JavaScript is a scripting language used for front-end web development.

• C++ is a high-level programming language used for system programming and software development.

• JavaScript is essential for creating interactive web pages and dynamic content.

• C++ is important for developing high-performance applications and operating systems.

JDK stands for Java Development Kit, which is a software development kit used for developing Java applications. JRE stands for Java Runtime Environment, which is required to run Java applications.

• JDK includes JRE along with development tools such as compiler, debugger, etc.

• JRE includes JVM (Java Virtual Machine) and libraries necessary for running Java applications.

• Developers use JDK to write, compile, and debug Java programs, while end-users only need JRE to run Java applica...read more

final, finalize, and finally are keywords in Java with different purposes.

• final is used to declare a constant value that cannot be modified

• finalize is a method used for garbage collection

• finally is a block used in exception handling to ensure a piece of code is always executed

Program to find the second largest number in an unsorted array

• Iterate through the array and keep track of the largest and second largest numbers

• Initialize the largest and second largest variables with the first two elements of the array

• Compare each element with the largest and second largest variables and update them if necessary

• Return the second largest number

Spring is a framework for building Java applications, while Spring Boot is a tool that simplifies the setup and configuration of Spring applications.

• Spring is a comprehensive framework that provides support for various functionalities like dependency injection, aspect-oriented programming, and more.

• Spring Boot is an opinionated tool that aims to simplify the setup and configuration of Spring applications by providing defaults and auto-configuration.

• Spring Boot includes embedd...read more

Spring Boot annotations @Component and @Bean have different purposes. @Component is used for auto-detection and instantiation of beans, while @Bean is used to explicitly define a bean.

• Use @Component to automatically detect and instantiate beans based on classpath scanning.

• Use @Bean to explicitly define a bean in a configuration class.

• @Component is a generic stereotype annotation while @Bean is a method-level annotation.

• @Component is used for classes, while @Bean is used for m...read more

Types of joins in SQL

• Inner join: returns only the matching rows from both tables

• Left join: returns all rows from the left table and matching rows from the right table

• Right join: returns all rows from the right table and matching rows from the left table

• Full outer join: returns all rows from both tables

• Cross join: returns the Cartesian product of both tables

Platform independence language refers to a programming language that can run on any platform without needing to be recompiled.

• Java is a platform independence language because it uses the Java Virtual Machine (JVM) to run on any platform.

• Platform independence allows Java programs to be written once and run anywhere, saving time and effort for developers.

• Other examples of platform independence languages include Python and Ruby.

Java is a high-level programming language known for its portability, security, and versatility.

• Java is platform-independent, meaning it can run on any device with a Java Virtual Machine (JVM).

• It is object-oriented, allowing for modular and reusable code.

• Java is widely used in web development, mobile applications, enterprise software, and more.

• Its strong security features make it a popular choice for building secure applications.

• Java has a large standard library and active com...read more

Spring REST annotations are used to simplify the development of RESTful web services in Spring framework.

• Annotations like @RestController, @RequestMapping, @GetMapping, @PostMapping, @PutMapping, @DeleteMapping are commonly used in Spring REST.

• These annotations help in mapping HTTP requests to specific handler methods, defining request mappings, and handling request parameters.

• For example, @GetMapping("/users") will map a GET request to /users endpoint to a specific method in...read more

Spring MVC Flow involves DispatcherServlet, HandlerMapping, Controller, Model, ViewResolver, and View.

• Client sends a request to DispatcherServlet.

• DispatcherServlet consults HandlerMapping to determine the appropriate Controller.

• Controller processes the request, interacts with Model, and returns a logical view name.

• DispatcherServlet consults ViewResolver to map the logical view name to an actual View.

• View renders the response and sends it back to the client.

Primary key uniquely identifies each record in a table, while unique key ensures that all values in a column are different.

• Primary key does not allow NULL values, while unique key allows one NULL value.

• A table can have only one primary key, but multiple unique keys.

• Primary key is automatically indexed, while unique key is not.

• Example: Primary key for a table of students could be student_id, while unique key could be email.

Internal working of HashMap

• HashMap is a data structure that stores key-value pairs

• It uses hashing to store and retrieve values

• The hash code of the key is used to find the index of the value in the array

• If there is a collision, the values are stored in a linked list at that index

• The load factor determines when the HashMap should resize

• The default load factor is 0.75

• HashMap is not thread-safe, use ConcurrentHashMap for thread safety

Object-oriented programming (OOP) is a programming paradigm that uses objects to represent real-world entities and their interactions.

• OOP allows for modular and reusable code.

• Encapsulation hides the internal details of an object.

• Inheritance allows for the creation of subclasses with shared characteristics.

• Polymorphism enables objects to take on multiple forms.

• Abstraction simplifies complex systems by focusing on essential details.

Static is important in Java for creating class-level variables and methods that can be accessed without creating an instance of the class.

• Static variables are shared among all instances of a class

• Static methods can be called without creating an object of the class

• Static blocks are used for initializing static variables

• Static keyword is used for creating nested classes

• Static import is used to import static members of a class

Operators in SQL and programming languages are used to perform various operations on data.

• SQL operators include arithmetic, comparison, logical, and bitwise operators.

• Programming language operators include arithmetic, assignment, comparison, logical, and bitwise operators.

• Examples of SQL operators are +, -, *, /, =, <>, >, <, AND, OR, NOT, &, |, ^.

• Examples of programming language operators are +, -, *, /, =, ==, !=, >, <, &&, ||, !, &, |, ^, +=, -=, *=, /=.

Oops concepts in Java

• Object-oriented programming

• Encapsulation

• Inheritance

• Polymorphism

• Abstraction

• Class

• Object

• Interface

• Constructor

• Method Overloading

• Method Overriding

Pillars of OOPS are Inheritance, Encapsulation, Abstraction, and Polymorphism.

• Inheritance: Allows a class to inherit properties and behavior from another class.

• Encapsulation: Bundling data and methods that operate on the data into a single unit.

• Abstraction: Hiding the complex implementation details and showing only the necessary features.

• Polymorphism: Ability of a method to do different things based on the object it is acting upon.

Exceptions are events that can be handled programmatically, while errors are typically unrecoverable issues.

• Exceptions are checked at compile time, while errors are unchecked.

• Exceptions are subclasses of Throwable, while errors are subclasses of Error.

• Examples of exceptions include NullPointerException, ArrayIndexOutOfBoundsException, while examples of errors include OutOfMemoryError, StackOverflowError.

JVM is the virtual machine that runs Java bytecode, providing platform independence.

• JVM stands for Java Virtual Machine

• It is responsible for interpreting Java bytecode and executing it on the underlying hardware

• JVM has components like Class Loader, Bytecode Verifier, Interpreter, Just-In-Time Compiler, and Garbage Collector

Spring container is responsible for managing the lifecycle of Spring beans and their dependencies.

• Spring container creates and manages the objects (beans) defined in the Spring configuration file.

• It injects dependencies, handles transactions, and manages the lifecycle of beans.

• There are two types of Spring containers: BeanFactory and ApplicationContext.

• ApplicationContext is preferred over BeanFactory as it provides more features like event handling, internationalization, etc.

HTML stands for Hypertext Markup Language.

• HTML is the standard markup language for creating web pages.

• It is used to structure content on the internet using a system of tags.

• Examples of HTML tags include <p> for paragraphs, <h1> for headings, and <a> for links.

Threads are lightweight processes within a program that can run concurrently, allowing for multitasking and improved performance.

• Threads allow multiple tasks to be executed simultaneously within a single program

• Threads share the same memory space, allowing for efficient communication and data sharing

• Examples include a web server handling multiple client requests concurrently, or a video game running animations and user input processing simultaneously

Serialisation in Java is the process of converting an object into a byte stream for storage or transmission.

• Serialisation allows objects to be saved and restored later.

• It is used in Java to enable objects to be sent over a network or stored in a file.

• The Serializable interface is implemented by classes to make them serializable.

• The ObjectOutputStream class is used to write objects to a stream.

• The ObjectInputStream class is used to read objects from a stream.

Int is an abbreviation for integer, which is a numerical data type in programming.

• Int is not a string, it is a data type used to represent whole numbers.

• In Java, int is a primitive data type and is declared using the keyword 'int'.

• Examples of int variables: int age = 25; int quantity = 10;