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Java Full Stack with React Interview Questions in Gurgaon

36 practice questions with answers for Java Full Stack with React interviews in Gurgaon.

Java Full Stack with React jobs in Gurgaon

Gurgaon (Gurugram) is home to many multinational, consulting, fintech and consumer-internet offices. Interviews often expect strong business understanding along with technical skills, especially for analytics and product-facing roles.

Below are 36 questions that match the mix of service, product and domain employers hiring java full stack developers in Gurgaon.

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01

What are cascade types and orphanRemoval in JPA?

JPA and HibernateMedium
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Cascade propagates operations from a parent to its children: PERSIST, MERGE, REMOVE, REFRESH, DETACH or ALL. For example, saving an Order with CascadeType.ALL also saves its items. orphanRemoval = true deletes a child row when it is removed from the parent's collection. Use them for true parent-child aggregates like order and items, but never cascade REMOVE on @ManyToOne or shared references like Category, or deleting one product could delete the category.
02

What is the contract between equals() and hashCode()?

Collections and StreamsMedium
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If two objects are equal according to equals(), they must return the same hashCode. Unequal objects may share a hash code, but fewer collisions give better performance. If you override equals without hashCode, HashMap and HashSet will fail to find objects that are logically equal. Base both methods on the same immutable fields; records and IDE or Lombok generation create them correctly.
03

What is the difference between controlled and uncontrolled components?

React FrontendMedium
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In a controlled component, form input values live in React state and change through onChange, so React is the single source of truth, which makes validation and conditional UI easy. In an uncontrolled component, the DOM keeps the value and you read it through a ref when needed, which needs less code and suits simple forms or file inputs. Libraries like React Hook Form use uncontrolled inputs for better performance in large forms.
04

When should you use useMemo and useCallback?

React FrontendMedium
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useMemo caches the result of an expensive calculation until its dependencies change, such as filtering and sorting a big list. useCallback caches a function reference, which matters when passing callbacks to children wrapped in React.memo or used in effect dependencies. Do not wrap everything, because memoization itself has a cost. The React Compiler, released as stable in 2025, can add much of this memoization automatically in supported projects.
05

Write a Flyway migration to add a column and index to an existing table.

JPA and HibernateMedium
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-- src/main/resources/db/migration/V3__add_sku_to_products.sql ALTER TABLE products ADD COLUMN sku VARCHAR(40); UPDATE products SET sku = CONCAT('SKU-', id) WHERE sku IS NULL; ALTER TABLE products ALTER COLUMN sku SET NOT NULL; CREATE UNIQUE INDEX ux_products_sku ON products (sku); # application.yml # spring.jpa.hibernate.ddl-auto: validate # Flyway runs pending V-scripts in order at startup.
06

Add request validation to a registration API.

REST APIs, Security and MicroservicesMedium
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public record RegisterRequest( @NotBlank @Size(max = 60) String name, @NotBlank @Email String email, @Pattern(regexp = "^[6-9]\\d{9}$", message = "Invalid mobile") String mobile, @Size(min = 8, max = 64) String password) {} @PostMapping("/api/auth/register") public ResponseEntity<Void> register(@Valid @RequestBody RegisterRequest req) { authService.register(req); return ResponseEntity.status(HttpStatus.CREATED).build(); } // Needs spring-boot-starter-validation. Errors raise // MethodArgumentNotValidException, mapped to 400 by the advice.
07

Write a production-friendly Dockerfile for a Spring Boot application.

Spring BootMedium
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FROM eclipse-temurin:21-jdk AS build WORKDIR /app COPY . . RUN ./mvnw -q -DskipTests package FROM eclipse-temurin:21-jre WORKDIR /app RUN useradd -r appuser USER appuser COPY --from=build /app/target/*.jar app.jar EXPOSE 8080 ENTRYPOINT ["java", "-XX:MaxRAMPercentage=75", "-jar", "app.jar"] # Multi-stage build keeps the image small; runs as non-root.
08

A report job builds a large string with + inside a loop and is very slow. What do you change?

Core JavaEasy
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Each + inside a loop creates a new String and copies the old content, giving roughly O(n squared) work. Replace it with one StringBuilder created before the loop, optionally with an initial capacity, and call append inside the loop. For joining collections, use String.join or Collectors.joining. For very large output, write directly to a BufferedWriter or stream instead of holding everything in memory.
09

How do profiles and application.yml work in Spring Boot?

Spring BootMedium
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Common settings go in application.yml, and environment-specific values go in files like application-dev.yml or application-prod.yml. You activate a profile with spring.profiles.active=prod, an environment variable SPRING_PROFILES_ACTIVE or a command-line argument. Profile files override the default values. Beans can also be limited with @Profile("dev"). Environment variables and command-line arguments have higher priority than files, which is useful in Docker and Kubernetes.
10

Compare monolithic and microservices architecture.

REST APIs, Security and MicroservicesMedium
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A monolith is one deployable application. It is simpler to build, test and debug, and suits small teams and early products. Microservices split the system into independently deployable services owned by separate teams, such as orders, payments and inventory, each with its own database. They allow independent scaling and releases but add network latency, distributed data, monitoring and deployment complexity. Many teams start with a modular monolith and split only when needed.
11

Find the top 3 highest-paid employees in each department.

SQL and DatabasesMedium
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SELECT department_id, name, salary FROM ( SELECT department_id, name, salary, DENSE_RANK() OVER ( PARTITION BY department_id ORDER BY salary DESC) AS rnk FROM employees ) ranked WHERE rnk <= 3 ORDER BY department_id, rnk; -- DENSE_RANK keeps ties; use ROW_NUMBER for exactly 3 rows.
12

How do you deep clone an object in JavaScript?

JavaScript, HTML and CSSMedium
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const original = { user: { name: 'Asha' }, tags: ['a'], joined: new Date() }; // Modern built-in (handles Date, Map, Set, cycles): const copy = structuredClone(original); // Spread is only a shallow copy: const shallow = { ...original }; shallow.user.name = 'Ravi'; // also changes original.user.name // JSON.parse(JSON.stringify(obj)) loses Dates, functions, // undefined and fails on circular references.
13

Your component keeps re-rendering in an infinite loop after calling an API. What is wrong?

React FrontendMedium
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Usually useEffect sets state and has a dependency that changes on every render, or has no dependency array at all. A common case is an object or function created inside the component and listed as a dependency, so it is new each time. Fix it by using a correct dependency array, moving the object outside the component, or memoizing it with useMemo or useCallback. Also check that you are not calling setState directly during render.
14

Explain the difference between map and flatMap in streams.

Collections and StreamsMedium
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map transforms each element into exactly one new element, so a Stream of orders mapped to customer names gives a Stream of String. flatMap transforms each element into a stream and flattens all of them into one stream. For example, orders.stream().flatMap(o -> o.getItems().stream()) gives every item from every order. Optional also has map and flatMap with the same idea.
15

How do derived query methods work in Spring Data JPA?

JPA and HibernateEasy
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Spring Data parses the method name in a repository interface and builds the query. For example, findByEmailAndActiveTrue(String email) or findTop5ByCategoryOrderByPriceDesc(String category). Supported keywords include And, Or, Between, LessThan, Like, In, IsNull and OrderBy. Return types can be Optional, List, Page or Stream. For complex logic, use @Query with JPQL or native SQL, because very long method names become hard to read.
16

Tell me about a difficult bug you fixed in a Java project.

Core JavaMedium
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Situation: our order API sometimes returned another user's cart. Task: I had to find the root cause quickly. Action: I reproduced it with a load test, found a Spring singleton service storing the current user in an instance field, and moved that state into a method parameter. I added a concurrent test to prevent regressions. Result: the issue disappeared and I shared the learning about stateless beans with the team.
17

Why should we hire you as a Java full stack developer?

JavaScript, HTML and CSSMedium
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I can contribute on both sides of a feature: I have built REST APIs with Spring Boot, JPA and MySQL, and responsive React screens that consume them. I write tests, use Git properly and have deployed my projects with Docker. I also learn quickly; I picked up Spring Security and JWT for my capstone in two weeks. I am looking for a team where I can grow into an engineer who owns features from design to production.
18

Call another microservice from Spring Boot using RestClient with a timeout.

REST APIs, Security and MicroservicesMedium
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@Bean RestClient inventoryClient(RestClient.Builder builder) { var factory = new SimpleClientHttpRequestFactory(); factory.setConnectTimeout(2000); factory.setReadTimeout(3000); return builder.baseUrl("http://inventory-service") .requestFactory(factory).build(); } public StockDto getStock(String sku) { return inventoryClient.get() .uri("/api/stock/{sku}", sku) .retrieve() .body(StockDto.class); } // RestClient (Boot 3.2+) replaces RestTemplate for new code; // use WebClient for reactive stacks.
19

Write CSS for a product grid that shows 1 column on mobile, 2 on tablet and 4 on desktop.

JavaScript, HTML and CSSEasy
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.grid { display: grid; grid-template-columns: 1fr; gap: 16px; padding: 0 16px; } @media (min-width: 640px) { .grid { grid-template-columns: repeat(2, 1fr); } } @media (min-width: 1024px) { .grid { grid-template-columns: repeat(4, 1fr); } } /* Mobile-first: base styles for small screens, then widen. */
20

What are fail-fast and fail-safe iterators?

Collections and StreamsMedium
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Fail-fast iterators, used by ArrayList and HashMap, track a modification count and throw ConcurrentModificationException if the collection is structurally changed during iteration, except through the iterator's own remove. Fail-safe or weakly consistent iterators, used by CopyOnWriteArrayList and ConcurrentHashMap, work on a snapshot or tolerate concurrent changes and never throw that exception, but they may not show the latest updates.
21

Describe the main JVM memory areas.

Core JavaMedium
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The heap stores objects and is shared by all threads; it is managed by the garbage collector and split into young and old generations. Each thread has its own stack holding method frames, local variables and references. Metaspace, in native memory since Java 8, stores class metadata. There is also the program counter per thread and the code cache for JIT-compiled code. Stack overflow comes from deep recursion, while OutOfMemoryError usually means heap or metaspace is full.
22

You get ConcurrentModificationException while removing items from a list inside a for-each loop. How do you fix it?

Collections and StreamsMedium
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The for-each loop uses a fail-fast iterator, and calling list.remove changes the modification count. Use list.removeIf(item -> item.isExpired()), which is clean and efficient, or use an explicit Iterator and call iterator.remove(). Another option is to collect the items to keep into a new list with a stream filter. If several threads modify the list, use a concurrent collection instead.
23

Users must upload files up to 200 MB. How do you design the upload API?

REST APIs, Security and MicroservicesMedium
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Avoid streaming large files through the application server. Generate a pre-signed URL for object storage like S3 or Azure Blob so the browser uploads directly, then the client calls the API to confirm and save the metadata. If uploads must go through Spring, raise spring.servlet.multipart.max-file-size, stream the input to storage instead of loading it into memory, validate type and size, and scan files for malware before use.
24

Compare promises and async/await.

JavaScript, HTML and CSSMedium
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A promise represents a value that will be available later, handled with then, catch and finally. async/await is syntax built on promises: an async function always returns a promise, and await pauses that function until the promise settles, so asynchronous code reads like synchronous code. Errors are handled with try/catch. Awaiting calls one by one is sequential, so use Promise.all for independent calls to run them in parallel.
25

Your team is starting a new React project. Would you use Create React App or something else?

JavaScript, HTML and CSSMedium
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Create React App is deprecated and no longer recommended. For a single-page app backed by a Spring Boot API, Vite is the usual choice because of its fast dev server and optimised builds. If you need server-side rendering, SEO or file-based routing, a framework like Next.js or React Router in framework mode is recommended by the React team. Choose based on SEO needs, hosting and the team's experience.
26

How do you version a REST API?

REST APIs, Security and MicroservicesMedium
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The most common approach is URI versioning, like /api/v1/orders and /api/v2/orders, because it is visible and easy to route and cache. Other options are a custom header or the Accept media type. Spring Framework 7 adds first-class API versioning support. Version only for breaking changes; adding optional fields is backward compatible. Keep old versions running for a published deprecation period, and document every version with OpenAPI.
27

What are the options for spring.jpa.hibernate.ddl-auto and which should be used in production?

JPA and HibernateEasy
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none does nothing, validate checks that the schema matches entities, update alters tables to add missing columns, create drops and recreates the schema at startup and create-drop also drops it at shutdown. update and create are fine for learning but risky in production because they cannot handle renames or data migrations safely. In production use validate or none, and manage schema changes with Flyway or Liquibase scripts.
28

Write a query that shows daily sales with a running total for the month.

SQL and DatabasesMedium
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SELECT order_date, SUM(amount) AS daily_sales, SUM(SUM(amount)) OVER ( ORDER BY order_date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ) AS running_total FROM orders WHERE order_date >= DATE '2026-10-01' AND order_date < DATE '2026-11-01' GROUP BY order_date ORDER BY order_date;
29

Return only a few columns using an interface-based projection.

JPA and HibernateMedium
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public interface ProductSummary { Long getId(); String getName(); BigDecimal getPrice(); } public interface ProductRepository extends JpaRepository<Product, Long> { List<ProductSummary> findByCategoryName(String category); @Query("select new com.shop.dto.PriceDto(p.name, p.price) from Product p where p.price < :max") List<PriceDto> cheaperThan(@Param("max") BigDecimal max); } // Projections select fewer columns and avoid loading full entities.
30

Use CompletableFuture to call two services in parallel and combine the results.

Core JavaHard
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CompletableFuture<User> userF = CompletableFuture.supplyAsync(() -> userClient.get(id), executor); CompletableFuture<List<Order>> ordersF = CompletableFuture.supplyAsync(() -> orderClient.byUser(id), executor); Profile profile = userF .thenCombine(ordersF, Profile::new) .orTimeout(2, TimeUnit.SECONDS) .exceptionally(ex -> Profile.empty()) .join(); // Pass a dedicated executor instead of the common pool for blocking I/O.
31

Implement pagination and sorting for a product list API.

JPA and HibernateMedium
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@GetMapping("/api/products") public Page<ProductDto> list( @RequestParam(defaultValue = "0") int page, @RequestParam(defaultValue = "20") int size, @RequestParam(defaultValue = "price") String sort) { Pageable pageable = PageRequest.of(page, Math.min(size, 100), Sort.by(sort).ascending()); return repository.findByActiveTrue(pageable).map(ProductDto::from); } // Repository: Page<Product> findByActiveTrue(Pageable pageable);
32

Why are semantic HTML and accessibility important?

JavaScript, HTML and CSSEasy
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Semantic elements like header, nav, main, article, button and label describe meaning, so screen readers, search engines and browsers understand the page. Use a real button instead of a clickable div so keyboard and focus work automatically. Add alt text to images, link labels to inputs, keep heading order logical and ensure enough colour contrast. Accessibility follows WCAG guidelines and improves SEO and usability for everyone.
33

Tell me about a time you delivered a feature under a tight deadline.

Spring BootMedium
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Situation: a client demo was moved forward by a week and the reporting module was not ready. Task: deliver the core report screens and APIs in five days. Action: I split the work into must-have and later items with my lead, reused existing query components, and wrote tests for the critical paths only. Result: the demo went well, and the remaining features shipped in the next sprint without bugs.
34

What is normalization? Explain 1NF, 2NF and 3NF.

SQL and DatabasesMedium
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Normalization organises tables to reduce redundancy and update anomalies. 1NF requires atomic values with no repeating groups. 2NF requires 1NF and that every non-key column depends on the whole primary key, not part of a composite key. 3NF requires 2NF and no transitive dependency, so non-key columns depend only on the key. For example, store customer city in the customers table, not in every order row. Reporting systems sometimes denormalize for speed.
35

How do indexes improve performance, and when can they hurt?

SQL and DatabasesMedium
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An index, usually a B-tree, lets the database find rows without scanning the whole table, which speeds up WHERE, JOIN and ORDER BY on indexed columns. Indexes cost disk space and slow down INSERT, UPDATE and DELETE because each index must also be updated. They help little on low-selectivity columns like a boolean flag. Functions on the column, such as WHERE LOWER(email) = ?, or a leading wildcard in LIKE also prevent normal index use.
36

Write a query to find the second highest salary from an employees table.

SQL and DatabasesEasy
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-- Using a subquery SELECT MAX(salary) AS second_highest FROM employees WHERE salary < (SELECT MAX(salary) FROM employees); -- Using DISTINCT with OFFSET SELECT DISTINCT salary FROM employees ORDER BY salary DESC LIMIT 1 OFFSET 1; -- The first query returns NULL when there is no second salary.

Companies with offices in Gurgaon (4)

Consulting

Accenture

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Hyderabad, Pune +2

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E-commerce & consumer tech

Walmart

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Chennai, Gurugram

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Consulting

Publicis Sapient

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Gurugram, Noida, Bengaluru

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IT services

EPAM Systems

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Hyderabad, Bengaluru, Pune +2

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Frequently asked questions

Which companies hire Java Full Stack with React professionals in Gurgaon?

Companies with large offices in Gurgaon include Accenture, Walmart, Publicis Sapient, EPAM Systems. Use their company pages below to practise employer-specific sets.

Are Java Full Stack with React interviews in Gurgaon different from other cities?

The questions depend more on the company than the city. Gurgaon's mix of employers decides the style: Interviews often expect strong business understanding along with technical skills, especially for analytics and product-facing roles

How do I find Java Full Stack with React jobs in Gurgaon?

Shortlist companies with Gurgaon offices, keep your CV focused on Java Full Stack with React projects, apply on company career pages and job portals with the Gurgaon filter, and practise the questions on this page before each interview.

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