100+ Java Full Stack Developer Interview Questions and Answers

Garbage collector is a program in Java that automatically manages memory by reclaiming unused memory.

• Garbage collector runs in the background and identifies objects that are no longer needed.

• It frees up memory by removing these unused objects, making the memory available for new objects.

• There are different types of garbage collectors in Java such as Serial, Parallel, CMS, G1, etc.

Java is a high-level programming language known for its platform independence and object-oriented features.

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

• Java is object-oriented, allowing for the creation of reusable code and modular programs

• Java is known for its robust standard library, which includes tools for networking, I/O, and more

The Map interface in Java represents a collection of key-value pairs, allowing efficient data retrieval based on keys.

• Maps store data in key-value pairs, e.g., Map<String, Integer> map = new HashMap<>();

• Common implementations include HashMap, TreeMap, and LinkedHashMap.

• Keys in a Map must be unique, while values can be duplicated.

• You can retrieve a value using its key, e.g., Integer value = map.get('key');

• Maps do not maintain any order of elements, except for TreeMap (sorted b...read more

Interface in Java is a blueprint of a class that defines a set of methods without implementation.

• An interface can be used to achieve abstraction in Java

• All methods in an interface are public and abstract by default

• A class can implement multiple interfaces

• Interfaces can also have default and static methods

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

Connecting a database to Spring involves configuring data sources, using Spring Data, and managing transactions effectively.

• Add Dependencies: Include Spring Data JPA and your database driver in your Maven or Gradle configuration. Example: <dependency> for MySQL.

• Configure Data Source: Set up your application.properties or application.yml file with database connection details. Example: spring.datasource.url=jdbc:mysql://localhost:3306/mydb.

• Create Entity Classes: Define JPA enti...read more

I have strong knowledge and experience in Java programming and UI development.

• Proficient in Java programming language, including core concepts like OOP, multithreading, and collections

• Skilled in developing UI using technologies like HTML, CSS, JavaScript, and frameworks like React or Angular

• Experience in integrating backend Java code with frontend UI for full stack development

• Familiar with UI design principles and responsive web design practices

Heap and stack memory are two types of memory in computer systems. Heap memory is used for dynamic memory allocation, while stack memory is used for static memory allocation.

• Heap memory is used for storing objects and is managed by the JVM. It is larger in size compared to stack memory.

• Stack memory is used for storing method calls, local variables, and is limited in size. It follows Last In First Out (LIFO) order.

• Example: When an object is created using the 'new' keyword, it ...read more

Attached entities are actively managed by the persistence context, while detached entities are no longer actively managed.

• Attached entities are being managed by the persistence context and any changes made to them will be automatically synchronized with the database.

• Detached entities are not being managed by the persistence context and changes made to them will not be automatically synchronized with the database.

• Entities become detached when the persistence context is closed,...read more

Object-oriented programming concepts in Java include inheritance, encapsulation, polymorphism, and abstraction.

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

• Encapsulation involves bundling data and methods that operate on the data into a single unit.

• Polymorphism allows objects to be treated as instances of their parent class.

• Abstraction hides the implementation details and only shows the necessary features of an object.

Java code to find second largest element in an array

• Sort the array in descending order

• Return the element at index 1 as the second largest element

Spring annotations are used to provide metadata to Spring framework classes and components.

• Annotations are used to configure Spring beans, dependency injection, AOP, and more

• Examples include @Component, @Autowired, @RequestMapping, @Service, @Repository

• Annotations help in reducing XML configuration and make code more readable and maintainable

Artificial Intelligence (AI) is the simulation of human intelligence processes by machines, especially computer systems.

• AI encompasses machine learning, natural language processing, and robotics.

• Examples include virtual assistants like Siri and Alexa.

• AI is used in healthcare for diagnostics and personalized medicine.

• Self-driving cars utilize AI for navigation and decision-making.

• AI algorithms can analyze large datasets to identify patterns.

Java is a versatile, object-oriented programming language used for building applications across various platforms.

• Platform Independence: Java applications can run on any device with a Java Virtual Machine (JVM). Example: Write once, run anywhere.

• Object-Oriented: Java supports concepts like inheritance, encapsulation, and polymorphism. Example: Creating classes and objects.

• Rich API: Java provides a comprehensive set of libraries for tasks like networking, I/O operations, and G...read more

I am excited about this role because it aligns with my skills and passion for developing innovative web applications.

• I have a strong background in Java and related technologies, which I believe will allow me to contribute effectively from day one.

• I am passionate about full stack development, as it allows me to work on both front-end and back-end, creating seamless user experiences.

• The company's commitment to innovation and quality resonates with my personal values, and I want...read more

Sort a list of students using Java Stream API

• Use the sorted() method to sort the list based on a comparator

• Use the Comparator.comparing() method to specify the sorting criteria

• Use the collect() method to collect the sorted elements back into a list

Microservices are a software architectural style that structures an application as a collection of small, loosely coupled services.

• Microservices are independent, self-contained components that can be developed, deployed, and scaled independently.

• Each microservice focuses on a specific business capability and communicates with other microservices through APIs.

• Microservices promote flexibility, scalability, and resilience in software development.

• Examples of microservices includ...read more

JDBC stands for Java Database Connectivity, which is a Java API for connecting and executing queries on a database.

• JDBC is used to connect Java applications to databases.

• Steps in JDBC include loading the driver, establishing a connection, creating a statement, executing queries, and handling results.

• Example: Class.forName("com.mysql.jdbc.Driver"); Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/database", "username", "password"); Statement stmt = con...read more

A lambda expression is a concise way to represent an anonymous function in Java, enabling functional programming features.

• Syntax: (parameters) -> expression or (parameters) -> { statements; }

• Used primarily to implement functional interfaces.

• Example: (x, y) -> x + y is a lambda that adds two numbers.

• Can be used with Java's Stream API for operations like filter, map, and reduce.

• Enhances code readability and reduces boilerplate code.

Multithreading is a programming concept that allows concurrent execution of multiple threads within a single process.

• Improves application performance by utilizing CPU resources efficiently.

• Allows multiple tasks to run simultaneously, e.g., downloading files while processing data.

• Java provides built-in support for multithreading through the Thread class and Runnable interface.

• Synchronization is crucial to prevent data inconsistency when multiple threads access shared resources...read more

There are three types of autowiring in Spring: byType, byName, and constructor.

• byType: Spring looks for a bean of the same type and injects it.

• byName: Spring looks for a bean with the same name and injects it.

• constructor: Spring looks for a constructor and injects the arguments.

Filter a List using Streams in Java

• Use the filter() method to apply a predicate to each element in the stream

• Use collect() method to convert the stream back to a List

• Example: List<String> names = Arrays.asList("Alice", "Bob", "Charlie"); List<String> filteredNames = names.stream().filter(name -> name.startsWith("A")).collect(Collectors.toList());

Sort an Employee HashMap based on keys or values

• Use TreeMap to automatically sort by keys

• Use Comparator to sort by values

• Convert HashMap to List and then sort

My expected CTC is based on my experience, skills, and the market rate for Java Full Stack Developers.

• My expected CTC is in line with industry standards for Java Full Stack Developers.

• I have considered my experience, skills, and the current market trends while determining my expected CTC.

• I am open to negotiation based on the overall compensation package offered by the company.

A final class is a class that cannot be extended or subclassed.

• Final classes are often used to prevent inheritance and ensure that the class cannot be modified or extended.

• Final classes are typically marked with the 'final' keyword in Java.

• Example: 'String' class in Java is a final class, meaning it cannot be extended.

Docker is a platform for containerization, while Kubernetes is an orchestration tool for managing those containers.

• Docker allows developers to package applications and their dependencies into containers.

• Kubernetes automates the deployment, scaling, and management of containerized applications.

• Docker containers are lightweight and can run consistently across different environments.

• Kubernetes provides features like load balancing, service discovery, and automated rollouts.

• Examp...read more

useEffect is a React hook that allows performing side effects in function components.

• useEffect is used to perform side effects in function components, such as data fetching, subscriptions, or manually changing the DOM.

• It runs after every render by default, but you can specify dependencies to control when it runs.

• To mimic componentDidMount, you can pass an empty array as the second argument to useEffect.

• To mimic componentWillUnmount, you can return a cleanup function from useE...read more

Promises are used for asynchronous programming in JavaScript, while Observables are used for reactive programming.

• Promises represent a single value that may be available now or in the future.

• Observables represent a stream of values that can be emitted over time.

• Promises are eager, meaning they start executing as soon as they are created.

• Observables are lazy, meaning they only start executing when subscribed to.

• Promises can be chained using .then() to handle success or failure...read more