Top 50 Java Full Stack Developer Interview Questions and Answers

Top 50 Java Full Stack Developer Interview Questions and Answers

14 Jun 2024
23 min read
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Java Full Stack Developer Interview Questions

Full stack developers are jack of all trades. They are skilled in frontend and backend. This is the reason why there's such a great demand for them in companies ranging from small startups to tech giants like Microsoft. To get a full-stack developer job with a good salary isn't a cakewalk.

The best reasonable way to be a Java full-stack developer is by working with a tech giant. For this, you have to appear and clear the interview. The questions you find in the interview may be tough and challenging. To help you in this journey, our experts have formed a detailed guide on the most commonly asked Java Full Stack Developer Interview Questions and Answers. It tries to get into the minds of interviewers and fetch the desired answers.

If you think we've left out anything, you may let us know in the comment section. We'll review our questions and modify accordingly.

Java full-stack developer Interview Questions for Beginners

1. What is Java Full Stack Development?

It refers to the development of both front-end means client-side and back-end means server-side parts of a web application. This includes Java programming language for server-side development or backend development, along with front-end technologies such as HTML, CSS, JavaScript, and frameworks such as Angular.

2. Explain the difference between front-end and back-end development.

Front-end is all about what clients see from the front and interact with the UI, like buttons and menus. The back-end is about making sure everything works easily behind the scenes, such as Backend languages like Java, C#, and Python.

3. What do you need to build a typical web application?

We need three important things: for the front end (React or Angular), for the back end (Spring Boot), and a place to store data ( MySQL).

4. What is the Java Virtual Machine (JVM), and why is it important?

The JVM is similar to an interpreter for Java. It helps Java programs run on different types of computers or frameworks. It is critical for running different Java applications.

5. What's a servlet, and why is it used in Java web development?

A servlet is an extraordinary kind of Java program that makes a difference servers do their work.

6. What is the Model-View-Controller (MVC) pattern?

MVC is like a blueprint that helps organize how an app works. It has 3 parts,

  • The model is like the app's memory, a database.
  • View which is what the user sees and interacts with, a User Interface
  • Controller which handles user actions and updates the model and view accordingly.

 What is the Model-View-Controller (MVC) pattern?

7. What's the Spring Framework, and why is it useful for Java?

Spring Framework is a toolkit for making Java applications. It makes Java coding easier by offering helpful features such as putting together different parts of the app, handling repetitive tasks, and making the app easier to maintain.

8. What are RESTful web services, and why are they important in Java?

These services are a way to make web apps communicate with each other using simple internet rules. They're important for making modern web apps in Java because they keep things simple and flexible.

9. What's Hibernate, and how does it help with databases in Java?

Hibernate is nothing but a translator between Java and databases. It makes it simpler to save and get information from a database by connecting Java objects with database tables.

10. Can you explain what dependency injection means in Spring?

It is like getting help from Spring to manage the parts of our applications that rely on each other. It makes it easier to swap out parts or test the application because everything isn't stuck together too tightly.

11. What's a singleton pattern, and why does it matter in Java?

It is like a rule that says a class can only have one instance. It's handy for things such as managing important stuff and these connections to databases efficiently.

12. What's the difference between GET and POST in web stuff?

GET is nothing but getting data from the server, like reading an article. POST is used for sending data to the server, like submitting a form or uploading a file.

13. What's SQL injection, and how can we stop it in Java?

SQL injection is a way for hackers to try to mess with databases by tricking them into running bad code. You can stop it by being careful with user inputs and using special techniques to handle them safely.

14. Why do we need a web container in Java apps?

A web container is such a traffic cop for web stuff in Java. It helps to manage the parts of a web app to make sure everything runs smoothly.

15. What's a session in web apps, and how do you can handle it in Java?

It is a memory card for a user's visit to a website. In Java, you can use cookies or special codes in the URL to keep track of this memory card.

Java full-stack developer Interview Questions for Intermediate

16. How will you develop a project from scratch? What technologies and languages would you need? OR What abilities a Java full-stack engineer ought to have?

  • Programming Languages(PL): Java full-stack developers should be knowledgeable in more than just one programming language. Java is a need along with Python, PHP, Ruby, C++, etc.
  • Front End languages: Java full stack developer Should be familiar with front-end technologies such as HTML5, CSS3, JavaScript, etc. Understanding of libraries like Angular, ReactJS, etc.
  • Databases: Java full stack developer should have Knowledge about Database Management Systems such as MongoDB, Oracle, MYSQL, etc., and caching mechanisms like Redis, Memcached, and Varnish.

17. Which language is the most preferred by Java Full Stack Developers?

Java itself is the first and foremost language that is preferred. Along with it, the Java full-stack developer should be proficient in other popular programming languages such as Python, Ruby, PHP, C++, etc.

18. What is Pair Programming? One biggest disadvantage?

  • It is a software development technique where two developers work together in the same machine system. One developer who writes the code is known as the driver and the other developer who checks the code is called the navigator.
  • One of the disadvantages is higher development costs because two resources are working on one single task at the same time.

19. What do you mean by CORS and how does it work?

  • CORS is Cross-Origin Resource Sharing and It is a W3C standard and HTTP header mechanism that allows a server to indicate origins such as domain, port, etc. from the requested one.
  • In this, When a browser sends a request to a different domain, it sends an origin header with the request. The server checks the “origin” header to decide whether or not to permit the requests.
  • In case the server permits the request, it sends an “Access-Control-Allow-Origin” header back to the browser to know that the request was successful.
  • This is known as a “preflight” request and it happens within the servers whenever a webpage attempts to create a cross-origin request.
  • CORS can be executed on the server side by setting reaction headers, which permit particular spaces to create requests.

20. What is a Callback Hell?

  • Callback Hell is asynchronous programming code i.e. multiple functions running simultaneously. The term depicts an expansive number of nested “if” statements or functions. In basic terms, Callback Hell is where you would like to apply numerous asynchronous functions.
  • The callback function leaves you with code that is difficult to read, maintain, and look making it more difficult to identify the flow of the application – the main obstacle to debugging. This is called Callback Hell.

21. Explain Long Polling

Long polling is a technique where the server maintains and manages a connection with the client until new data is available. It is used for real-time applications, allowing instant updates without the need for constant client requests. e.g. chat applications, stocks, or multiplayer games.

22. How to enhance a website’s scalability and efficiency?

We can use some of the following ways to optimize the efficiency of a website:

  • Reducing DNS lookup
  • Optimising Code
  • Use Content Delivery Network (CDN).
  • Avoid URL redirects as much as possible
  • Avoid duplicating codes and unnecessary images
  • Leverage browser caching
  • Avoid inline JavaScript and CSS

23. Comparison between Java and Python

here’s the difference between Java and Python:

Pointers Java Python

  • Code Java has longer code lines Fewer lines of code are generally used in Python
  • Working Speed Java is faster in speed as compared to Python It uses an interpreter hence it is slower and also determines the data type at run time

Data Types Static Dynamic

  • Inheritance Partially supports multiple inheritances through interfaces Supports multiple inheritance
  • Framework Java has a large number of Frameworks. The popular Frameworks are Spring, Hibernate, etc. Compared to Java, Python has a lower number of Frameworks. The popular ones are Django and Flask
  • Syntax The syntax is complex. Errors can be found if you miss semicolons or curly brackets. The syntax is easy to remember. It is similar to human language.
  • Databases Java Database Network (JDBC) is broadly used to connect with databases.
  • Key Highlights Self-memory management, Robust, Platform independent Less line no.

24. Major Java Features

The major features of Java as one of the most well-known programming languages and interview questions for Java full-stack engineers are below:

  • Object-oriented: Java is an object-oriented programming language where classes and methods describe the state and behavior of an object.
  • Portable: Java programs can be converted into Java bytecodes which can be executed on any platform without any dependencies.
  • Independent platform:Java goes with the rule of 'write once, run anywhere' as it is supported on different stages like Linux, Windows, Mac, etc.
  • Robust in nature: Memory leaks in Java are denied due to solid memory management and automatic garbage collection.
  • Interpreted: The Java compiler converts the codes into Java bytecodes which are then interpreted and executed by the Java Interpreter.

25. Describe the class in Java

  • Class in Java is a blueprint for creating objects that have similar attributes and behaviors. It is a basic concept in object-oriented programming and is used to summarize data and behavior into a single unit.
  • A class contains variables, methods, and constructors that define its properties and behavior. The variables in a class represent the state or data of the object.
  • The methods show the actions that can be performed on the object.

26. What is CI (Continuous Integration)? What is continuous integration and continuous delivery (CI/CD)?

CI is nothing but an abbreviation for Continuous integration. It is a computer program development practice in which frequent and disconnected changes are immediately tested, and reported to the codebase. This helps the developer to identify issues at the earlier stage of development, makes it easier to fix bugs, and curtails problems at the merge for the release.

27. Is there a way to decrease the load time of a web application?

Here are some ways in which the load time of a web application can be decreased

  • Image sizing and format optimization
  • Caching of the web pages
  • Avoiding extra plugins
  • Reduction in HTTP requests
  • Avoiding of Inline JS and CSS files
  • Content Delivery Network (CDN)

28. What is Promise and explain its states?

Promise in Java is not a built-in language but includes programming concepts related to asynchronous programming and concurrency. It is a representation of a value that may not be available yet but will be resolved in the future. It’s a way to write code that can be later executed asynchronously and then wait for the result.

  • Pending- Neither rejected nor fulfilled
  • Fulfilled- Promise action is fulfilled successfully
  • Rejected: Promise action is failed to be completed
  • Settled: Either the action is fulfilled or rejected

29. Difference between GET and POST

Difference between GET and POST

30. In Java, what is a connection leak? How can you fix this?

  • When a connection is acquired without being closed, then a connection leak happens.
  • The ‘leak’ is because each time it happens, one less connection is available for re-use.
  • Prevention of connection leaks is important during testing for occurring in a production environment.
  • Connection Leak in Java performs while using Connection Pool.
  • If there is an area of code that is not connected properly, every time that area code is executed, a connection will “leak” from the pool.

How to fix connection leaks:

  • The first step is to verify where the connection leaks occurred.
  • This can be done through code inspection.
  • Once the leaks are identified, inspect the code to find any connections that are not properly closed.
  • Look for instances where connection objects are created but its not explicitly closed or returned to a connection pool.


Connection connection = null;
 try {
connection = DriverManager.getConnection (url, username, password);
// Use the connection
 catch (SQLException e)
// Handle exceptions
 } finally {
if (connection != null) 
catch (SQLException e) 
// Handle exceptions


31. What is a deadlock in Java?

A deadlock is a programming situation where two or more threads are blocked forever. This situation occurred with at least two threads or two or more resources.

32. How to avoid deadlock in Java?

  • First Avoid nested locks- Do not give locks to multiple threads if one of the threads is already locked.
  • Second, Avoid unnecessary locks: It is recommended to lock the necessary members since it can result in a deadlock in Java.
  • Third, Using Thread Join (): If one thread is waiting to complete., a deadlock problem develops. If the situation exists, we can utilize Thread. join() and the max. execution time.

33. What is RESTful API?

REST is an acronym for Representational State Transfer which shows an architectural style widely employed in the development of web services. It depends on the use of HTTP requests to interact with and manipulate data. REST manages operations such as creating, updating, reading, and deleting data.

34. Explain the difference between the inner class and the subclass.

An inner class is nothing but a class defined within another class in Java. inner class is tightly coupled with the enclosing class and can access its members, including private ones also. Inner classes are used for better organization and encapsulation of related code.On the other hand, a subclass inherits properties and behaviors from a superclass. It extends the functionality of the superclass. Itcan access protected and public members of the superclass, but not private ones unless provided with public or protected getter/setter methods. Subclassing is used in code reuse and polymorphism in object-oriented programming.

35. Java doesn’t support multiple Inheritance. Why?

To maintain a simpler and more manageable class hierarchy, Java does not support multiple inheritances to avoid ambiguity and complexity that arise from inheriting multiple classes.

36. What is the difference between Java and C++?

 What is the difference between Java and C++?

Java full-stack developer Interview Questions for Experienced

37. Can you tell me what are the latest trends in Full Stack Development? Also, how do you keep yourself updated about the new trends in the industry?

Some of the latest trends in Full Stack Development are as follows:

  • Serverless Architecture: It is used toUtilize cloud platforms for backend services without managing servers.
  • Microservices: It is used to break down applications into small, independent services for scalability and agility.
  • Progressive Web Applications (PWAs): It is used to build web applications that offer native-like experiences with offline capabilities.
  • Containerization: It uses technologies such as Docker for efficient deployment and management of applications.
  • AI and Machine Learning Integration: It incorporates artificial intelligence and machine learning capabilities into full-stack development.

38. State difference between GraphQL and REST

State difference between GraphQL and REST

39. Features of GraphQL REST

  • GraphQL is first developed by Facebook.
  • GraphQL REST is an application layer server-side technology.
  • It is used for executing queries with existing data.
  • GraphQL is a software architectural style.
  • REST is defined as a set of constraints for creating Web services. The constraints are as follows
  • Images are a key feature of GraphQL REST, a Type of architecture such as Client-driven architecture and Server-driven architecture
  • It has a growing community It has a large community
  • It's development speed is Fast

40. What is ‘use strict’ in Java?

use strict is a statement that is used to enable strict mode to scripts or individual functions.

41. What are the advantages and drawbacks of using “use strict”?

The advantages of using “use strict” are:

  • Impossible to create global variables, hence it is good for security purposes
  • It wants a unique function parameter name.
  • It Stops the functioning of features which creates confusion which creates complexity.
  • It Catches common coding bloopers, throwing exceptions

Disadvantages of using “use strict” are:

  • It does not have many features that the developers might be using.
  • It has no access to function. caller and function.arguments

42. What is the SOLID principle in Java?

SOLID stands :

  • Single Responsibility Principle (SRP): In this Only one reason is required for a class to change.
  • Open-Closed Principle (OCP): In Software entities such as classes, modules, functions, etc.
  • Liskov Substitution Principle (LSP): In this, Objects of a superclass should be replaceable with objects of its subclasses without affecting the correctness of the code.
  • Interface Segregation Principle (ISP): It avoids compelling clients to rely on interfaces they don’t utilize.
  • Dependency Inversion Principle (DIP): It Promotes a design where higher-level and lower-level modules depend on abstractions.

43. What is a critical section?

A critical section is a specific part of the code where shared resources are accessed or modified. critical section needs to be executed by only one thread at a time to avoid conflicts and maintain data integrity. To success this, synchronization techniques such as synchronized blocks or locks are used

44. Mention the difference between Iterator and Enumeration.

difference between Iterator and Enumeration

45. What is multithreading?

Multithreading refers to the ability of a program to perform multiple tasks concurrently, where each task falls under a separate thread. multithreading allows developers to handle multiple tasks simultaneously e.g. handling user interfaces, performing background operations, and optimizing resource utilization in applications.

46. Difference between ArrayList and Vector in Java

Difference between ArrayList and Vector in Java

47. What is Docker? What are some of the uses of Docker?

It is a tool that wraps Java applications and their dependencies into portable containers. These containers can be easily deployed on different computers with consistency maintained and creating reliability in executing Java applications regardless of the underlying environment.

Some advantages of docker :

  • It provides a consistent development for Java applications.
  • It Ensures that Java applications can be shared and deployed consistently across different systems.
  • Docker containers managed controlled testing and debugging of Java application components.
  • Docker supports the implementation of microservices-based architecture in Java, making services more manageable and deployable.

48. What is the difference between a constructor and a destructor in Java

What is the difference between a constructor and a destructor in Java

49. How null is different from undefined in JavaScript?

1. Null:

Null is nothing but a variable assigned with a null value. If you use it with the type of operator it will gives the result as an object. you should never assign a variable to null because the programmer uses it to represent a variable that has no value. Note that JavaScript will never automatically assign the value to null.

2. Undefined:

Undefined is nothing but the variable is declared but not assigned any value to it. It is a variable that does not exist. If you use it with typeof operator it will gives the result undefined. hence It is not valid in JSON.


var var1  
var var2 = null //assigning null value to the variable var2  
console.log(`var1 : ${var1}, type : ${typeof(var1)}`)  
console.log(`var2 : ${var2}, type : ${typeof(var2)}`)      

50. What is double brace initialization in Java and where it is used?

  • The double brace initialization is a combination of two separate processes.
  • There are two consecutive curly braces "{{" involved in it.
  • The very first curly brace represents the creation of an anonymous inner class.
  • The second curly brace will not be considered in such a case.
  • It is creating an anonymous inner class.
  • The second curly brace depicts an initialization block that you have seen in it as a class for initialization.
  • When you use the initialization block for an anonymous inner class it becomes Java double brace initialization.
  • Here, The inner class has a reference to the enclosing outer class.
  • then you can use the reference by using this pointer.
  • It is used to initialize collections.


import java.util.*;  
public class Demo  
public static void main(String args[])  
Map> map = new HashMap > {{  
put ("STUDENTS", new HashMap() {{  
put("Chinmay", 300);  
put("Vedant", 50);  
put("Smrita", 100);  
put("Gourav", 40);  

So in this article, we have learned 50 Java Full Stack Developer Interview Questions and Answers. I hope you enjoyed learning these concepts while programming with Java. Feel free to ask any questions from your side. Your valuable feedback or comments about this Java article are always welcome. Also, consider taking a Java Programming Course for a better understanding of Java concepts. 


Q1. How long does it take to become a full stack Java Developer?

You can become a Full Stack Developer in 3 months, 6 months, or 9 months.

Q2. What is the qualification for Java full-stack developer?

To develop your coding skills further, consider enrolling in a bachelor's or master's degree program in a related field.

Q3. What is the salary of a Java full-stack developer?

The average salary for Full Stack Java Developer is ₹5,35,000 per year in the India.
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