100+ Fullstack Java Developer Interview Questions and Answers

A cookie is a small piece of data stored on the user's computer by the web browser, used to track user activity and personalize user experience.

• Cookies are used to store user preferences, login information, and shopping cart items.

• They help websites remember users and their preferences, making the browsing experience more personalized.

• Cookies can also be used for tracking user behavior, such as analyzing website traffic and targeting advertisements.

• Cookies can be session-base...read more

Containerization simplifies deployment by packaging applications with their dependencies, ensuring consistency across environments.

• Use Docker to create container images that encapsulate your application and its dependencies.

• Leverage Docker Compose for multi-container applications, allowing you to define services in a single YAML file.

• Utilize Kubernetes for orchestration, managing container deployment, scaling, and networking.

• Implement CI/CD pipelines with tools like Jenkins o...read more

Developing REST APIs and microservices involves designing, implementing, and deploying scalable web services using Java technologies.

• Use Spring Boot to create RESTful services quickly with minimal configuration.

• Define endpoints using @RestController and @RequestMapping annotations.

• Utilize JPA/Hibernate for database interactions and entity management.

• Implement security using Spring Security for authentication and authorization.

• Use Docker to containerize microservices for easy ...read more

A palindrome program in Java checks if a given string is the same when read forwards and backwards.

• Convert the string to lowercase to ignore case sensitivity.

• Use two pointers, one starting from the beginning and the other from the end of the string.

• Compare the characters at the two pointers, moving them towards the center until they meet or cross each other.

• If at any point the characters are not equal, the string is not a palindrome.

• If the pointers meet or cross each other, t...read more

In Angular, component values can be passed using Input properties, Output events, and services for state management.

• Use @Input() decorator to pass data from parent to child component. Example: <child-component [data]='parentData'></child-component>

• Use @Output() decorator to emit events from child to parent component. Example: @Output() eventEmitter = new EventEmitter();

• Utilize Angular services for sharing data between components. Example: Create a service and inject it into c...read more

Various annotations are used in Spring Boot for different purposes.

• 1. @RestController - Used to define RESTful web services.

• 2. @RequestMapping - Maps web requests to specific handler methods.

• 3. @Autowired - Injects dependencies into a Spring bean.

• 4. @Component - Indicates a class is a Spring component.

• 5. @Service - Indicates a class is a Spring service.

• 6. @Repository - Indicates a class is a Spring repository.

• 7. @Configuration - Indicates a class contains Spring configuration...read more

Implementing CRUD operations in Spring Boot involves creating RESTful APIs for data management.

• 1. Create a Spring Boot project using Spring Initializr with dependencies: Spring Web, Spring Data JPA, and H2 Database.

• 2. Define an entity class, e.g., 'User', with fields like id, name, and email.

• 3. Create a repository interface extending JpaRepository<User, Long> for database operations.

• 4. Implement a service class to handle business logic and interact with the repository.

• 5. Crea...read more

Autoboxing is the automatic conversion of primitive data types to their corresponding object wrapper classes.

• Autoboxing allows primitive data types to be used as objects.

• Auto-unboxing is the reverse process of autoboxing.

• Autoboxing and auto-unboxing are performed automatically by the compiler.

• Example: int i = 10; Integer j = i; // autoboxing

• Example: Integer j = 10; int i = j; // auto-unboxing

Write a program using class function and condition

• Create a class with relevant functions

• Use conditional statements to execute specific code

• Example: class Calculator with add() function and if-else statement to check input

• Example: class Student with calculateGrade() function and switch statement to assign grade

Product based companies create and sell physical or digital products, while service based companies provide services to clients.

• Product based companies focus on developing and selling products to customers.

• Service based companies offer services to clients, such as consulting, IT support, or marketing.

• Product based companies typically have a tangible product to sell, like Apple selling iPhones.

• Service based companies rely on the expertise and skills of their employees to deliv...read more

Design a scalable system for millions of users

• Use microservices architecture to break down the system into smaller, independent services

• Implement load balancing to distribute traffic evenly across servers

• Utilize caching mechanisms to reduce database load and improve performance

• Use horizontal scaling by adding more servers to handle increased traffic

• Implement monitoring and alerting systems to track system performance and detect issues proactively

Factory pattern creates objects without exposing the instantiation logic, while Abstract Factory pattern provides an interface for creating families of related objects.

• Factory pattern is a creational design pattern that provides a way to create objects without specifying the exact class of object that will be created.

• Abstract Factory pattern is a creational design pattern that provides an interface for creating families of related or dependent objects without specifying their...read more

Front end developers work on the user interface and user experience of a website or application, while back end developers work on the server-side functionality and database management.

• Front end developers use HTML, CSS, and JavaScript to create the visual and interactive elements of a website or application.

• Back end developers use programming languages like Java, Python, and PHP to create the server-side logic and database management.

• Fullstack developers have knowledge of bo...read more

Find duplicate characters in a given array of strings

• Iterate through each string in the array

• For each string, iterate through each character and store the count in a hashmap

• If the count of any character is greater than 1, it is a duplicate

Find the second largest element from array of strings

• Sort the array in descending order

• Access the element at index 1 to get the second largest element

Indexes in SQL are data structures that improve the speed of data retrieval operations on a database table.

• Indexes are created on columns in a database table to quickly retrieve data based on the values in those columns.

• They help in reducing the time taken to fetch data by acting as a roadmap to the data.

• Examples of indexes include primary keys, unique keys, and non-unique indexes.

A function in JavaScript is a block of code that can be defined and called to perform a specific task.

• Functions can be declared using the 'function' keyword followed by a name and a set of parentheses for parameters.

• Functions can also be defined as arrow functions using the '=>' syntax.

• Functions can be called by using their name followed by parentheses containing any required arguments.

Inheritance in Java allows a class to inherit attributes and methods from another class.

• Inheritance is a key feature of object-oriented programming in Java.

• It promotes code reusability by allowing a new class to use the properties and methods of an existing class.

• The class that is inherited from is called the superclass or parent class, while the class that inherits is called the subclass or child class.

• Example: class Dog extends Animal { // Dog inherits from Animal }

Generate all unique permutations of a given collection of distinct integers.

• Use backtracking to explore all possible arrangements.

• Start with an empty permutation and build it step by step.

• Example: For input [1, 2], output is ['12', '21'].

• Ensure to mark elements as used to avoid duplicates.

React is a JavaScript library for building user interfaces. Deployment can be done using various methods.

• React features include virtual DOM, component-based architecture, JSX syntax, and state management.

• Deployment can be done using tools like Heroku, Netlify, AWS, or manually by building and serving static files.

• Continuous integration and deployment (CI/CD) pipelines can be set up to automate the deployment process.

• Server-side rendering can be used for better SEO and perform...read more

Joins in SQL are used to combine data from two or more tables based on a related column.

• Joins are used to retrieve data from multiple tables in a single query.

• There are different types of joins such as inner join, left join, right join, and full outer join.

• 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 ...read more

An interface in Java is a collection of abstract methods and constants that can be implemented by a class.

• Interfaces are used to achieve abstraction and provide a way to implement multiple inheritance in Java.

• All methods in an interface are abstract by default and cannot have a body.

• A class can implement multiple interfaces but can only extend one class.

• Interfaces can also have default and static methods with a body.

• Example: interface Shape { void draw(); }

• Example: class Circ...read more

There are two ways of Exception handling in Java - using try-catch blocks and using throws keyword.

• 1. Using try-catch blocks to catch and handle exceptions

• 2. Using throws keyword to declare exceptions to be thrown to the calling method

API gateway in microservices acts as a single entry point for all client requests, providing routing, authentication, and other functionalities.

• API gateway handles all client requests and routes them to the appropriate microservice

• It can perform authentication, rate limiting, load balancing, and caching

• Helps in decoupling clients from individual microservices, simplifying the overall architecture

Understanding GET and POST requests is crucial for web development, especially in RESTful APIs.

• GET requests retrieve data from a server. Example: fetching user details from '/api/users'.

• POST requests send data to a server to create or update resources. Example: submitting a form to '/api/users'.

• GET requests can be cached, while POST requests are not cached by default.

• GET requests have length restrictions due to URL length limits, whereas POST requests can handle larger payloa...read more

Flex in CSS is a layout module that allows elements to adjust their sizes dynamically to fill available space.

• Flexbox is used to create flexible layouts where items can grow or shrink to fill the available space.

• It provides a more efficient way to layout, align, and distribute space among items in a container.

• Flex properties like flex-grow, flex-shrink, and flex-basis control how items behave within a flex container.

• Example: Using 'display: flex;' on a container and 'flex: 1;...read more

JavaScript is a high-level, interpreted programming language that is used to make web pages interactive and dynamic.

• JavaScript is commonly used for client-side web development.

• It can be used to create interactive features like animations, form validation, and dynamic content.

• JavaScript can also be used on the server-side with platforms like Node.js.

• It is a versatile language that is supported by all major web browsers.

• JavaScript is often used in conjunction with HTML and CSS ...read more