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Java Full Stack with React Interview Questions in Noida

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

Java Full Stack with React jobs in Noida

Noida is a major IT and IT-services hub in Delhi NCR with large campuses of service companies, product firms and fast-growing start-ups along the Noida–Greater Noida Expressway. Freshers often find their first role here, and many teams run hybrid work.

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

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01

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.
02

How do code splitting and lazy loading work in React?

React FrontendMedium
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Code splitting breaks the JavaScript bundle into smaller chunks loaded on demand, which improves first load time. React.lazy with a dynamic import, such as const Reports = lazy(() => import('./Reports')), loads the component only when it renders, and Suspense shows a fallback while it loads. Splitting by route is the most common pattern. Bundlers like Vite create the chunks automatically from dynamic imports.
03

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.
04

Explain the different types of SQL joins.

SQL and DatabasesEasy
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INNER JOIN returns only rows that match in both tables. LEFT JOIN returns all rows from the left table plus matches from the right, with nulls where there is no match. RIGHT JOIN is the reverse. FULL OUTER JOIN returns all rows from both sides, which MySQL does not support directly. CROSS JOIN returns every combination. A self join joins a table to itself, such as employees and their managers.
05

When would you use the Context API and when a state library like Redux Toolkit or Zustand?

React FrontendMedium
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Context is good for passing low-frequency global values such as theme, language or the logged-in user without prop drilling. Every consumer re-renders when the context value changes, so it is not ideal for fast-changing data. Redux Toolkit or Zustand suit larger shared client state with many updates, selectors and dev tools. Server data like API responses is often best handled by TanStack Query, which adds caching and refetching.
06

Your React app gets 403 Forbidden on POST requests to Spring Boot, but GET works. What is the likely cause?

REST APIs, Security and MicroservicesMedium
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With Spring Security enabled, CSRF protection is on by default and blocks POST, PUT and DELETE that lack a CSRF token, while GET is allowed. For a stateless JWT API, disable CSRF in the SecurityFilterChain. If you use session cookies, keep CSRF and send the token with CookieCsrfTokenRepository. Also check CORS, because a rejected preflight OPTIONS request or a missing role in authorization rules can produce the same symptom.
07

What are the correct and incorrect ways to use Optional?

Collections and StreamsMedium
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Use Optional as a return type when a value may be absent, and consume it with map, filter, orElse, orElseGet or orElseThrow. Avoid calling get() without checking, avoid Optional fields in entities or DTOs, avoid Optional parameters and never return null from a method that returns Optional. Prefer orElseGet over orElse when the default is expensive, because orElse always evaluates its argument.
08

When would you use Flexbox and when CSS Grid?

JavaScript, HTML and CSSEasy
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Flexbox is one-dimensional: it arranges items in a row or a column and is great for navbars, button groups, centring and card rows that wrap. Grid is two-dimensional: it controls rows and columns together, ideal for page layouts, dashboards and galleries with grid-template-areas. They work well together, for example a Grid page layout with Flexbox inside each card. Both reduce the need for floats and positioning hacks.
09

Build a login form with basic validation in React.

React FrontendMedium
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function LoginForm({ onLogin }) { const [form, setForm] = useState({ email: '', password: '' }); const [errors, setErrors] = useState({}); const handleChange = e => setForm({ ...form, [e.target.name]: e.target.value }); const handleSubmit = e => { e.preventDefault(); const errs = {}; if (!/^\S+@\S+\.\S+$/.test(form.email)) errs.email = 'Enter a valid email'; if (form.password.length < 8) errs.password = 'Minimum 8 characters'; setErrors(errs); if (Object.keys(errs).length === 0) onLogin(form); }; return ( <form onSubmit={handleSubmit}> <input name="email" value={form.email} onChange={handleChange} /> {errors.email && <span>{errors.email}</span>} <input name="password" type="password" value={form.password} onChange={handleChange} /> {errors.password && <span>{errors.password}</span>} <button type="submit">Login</button> </form> ); }
10

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.
11

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.
12

How does the this keyword work, and how do arrow functions change it?

JavaScript, HTML and CSSMedium
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In a regular function, this depends on how the function is called: the object before the dot in a method call, undefined in strict mode for a plain call, the new object with new, or a value set by call, apply or bind. Arrow functions do not have their own this; they use this from the surrounding scope. That makes arrows ideal for callbacks inside methods, but unsuitable as object methods that need their own this.
13

Write a record and use pattern matching in a switch expression.

Core JavaMedium
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sealed interface Payment permits Card, Upi {} record Card(String number, double amount) implements Payment {} record Upi(String vpa, double amount) implements Payment {} static String describe(Payment p) { return switch (p) { case Card c when c.amount() > 50000 -> "High value card"; case Card c -> "Card ending " + c.number().substring(12); case Upi u -> "UPI to " + u.vpa(); }; } // Sealed types make the switch exhaustive without a default branch (Java 21).
14

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.
15

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.
16

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.
17

Call three APIs in parallel and handle failure of any one gracefully.

JavaScript, HTML and CSSMedium
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async function loadDashboard() { const results = await Promise.allSettled([ fetch('/api/orders').then(r => r.json()), fetch('/api/stats').then(r => r.json()), fetch('/api/alerts').then(r => r.json()), ]); const [orders, stats, alerts] = results.map(r => r.status === 'fulfilled' ? r.value : null); return { orders, stats, alerts }; } // Promise.all rejects on the first failure; // allSettled lets the page show partial data.
18

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;
19

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.
20

Write a repository query that loads orders with their items in one query.

JPA and HibernateMedium
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public interface OrderRepository extends JpaRepository<Order, Long> { @Query(""" select distinct o from Order o join fetch o.items i where o.customer.id = :customerId """) List<Order> findWithItems(@Param("customerId") Long customerId); @EntityGraph(attributePaths = {"items", "customer"}) Optional<Order> findWithGraphById(Long id); }
21

What is the difference between persist and merge, and between save and saveAndFlush?

JPA and HibernateMedium
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persist makes a new entity managed and assigns its ID; it fails for detached entities. merge copies the state of a detached entity onto a managed copy and returns that copy. Spring Data save calls persist for new entities and merge otherwise. saveAndFlush also calls flush, pushing pending SQL to the database immediately, which helps when you need a constraint error or trigger result now. The commit still happens at the end of the transaction.
22

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.
23

What is Spring Boot and how is it different from the Spring Framework?

Spring BootEasy
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Spring Framework provides dependency injection, MVC, data access and transactions, but traditionally needed a lot of manual configuration and an external server. Spring Boot sits on top of Spring and adds auto-configuration, starter dependencies, an embedded Tomcat, Jetty or Undertow server, externalised configuration and production features like Actuator. You can run an application as a single executable jar with java -jar, which makes it ideal for microservices and containers.
24

How do you handle a requirement that is unclear or keeps changing?

REST APIs, Security and MicroservicesMedium
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Situation: a product manager asked for a discount feature with vague rules. Task: build it without wasting effort. Action: I wrote down my understanding with examples, asked specific questions about edge cases like stacking coupons, and built the rules as configurable data instead of hard-coded logic. I shared a small demo early for feedback. Result: two rule changes later in the sprint needed only configuration updates, not code changes.
25

Explain final, finally and finalize.

Core JavaEasy
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final is a keyword: a final variable cannot be reassigned, a final method cannot be overridden and a final class cannot be extended. finally is a block after try or catch that always runs, used for cleanup, although try-with-resources is now preferred. finalize() was an Object method called before garbage collection; it is deprecated for removal because its timing is unpredictable. Use Cleaner or try-with-resources instead.
26

Using streams, group employees by department and count them.

Collections and StreamsMedium
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Map<String, Long> countByDept = employees.stream() .collect(Collectors.groupingBy( Employee::getDepartment, Collectors.counting())); // Average salary per department: Map<String, Double> avgSalary = employees.stream() .collect(Collectors.groupingBy( Employee::getDepartment, Collectors.averagingDouble(Employee::getSalary))); // Use TreeMap::new as the second argument to get sorted keys.
27

Users in different countries see wrong order times. How do you handle dates and time zones in Java?

Core JavaMedium
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Store timestamps in UTC using Instant or OffsetDateTime, and map them to TIMESTAMP WITH TIME ZONE or a UTC timestamp column. Convert to the user's zone only when displaying, using ZonedDateTime with ZoneId such as Asia/Kolkata. Avoid java.util.Date and SimpleDateFormat, which are mutable and not thread-safe. Use DateTimeFormatter, send ISO-8601 strings in JSON and set hibernate.jdbc.time_zone to UTC.
28

What is the difference between checked and unchecked exceptions?

Core JavaEasy
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Checked exceptions extend Exception (but not RuntimeException) and must be caught or declared with throws, for example IOException or SQLException. Unchecked exceptions extend RuntimeException, such as NullPointerException or IllegalArgumentException, and the compiler does not force handling. Use checked exceptions for recoverable conditions the caller should handle, and unchecked ones for programming errors. Spring prefers unchecked exceptions, for example DataAccessException, to keep service code clean.
29

You are loading about five lakh records into an ArrayList and a HashMap and memory spikes during loading. What can you do?

Collections and StreamsMedium
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Both collections resize by copying when they grow, which causes temporary memory spikes. Pre-size them, for example new ArrayList<>(500000) and HashMap with capacity of expected size divided by 0.75. Better still, avoid holding everything at once: process the data in batches or stream it from the database with pagination. Use primitive-friendly structures or IntStream where possible to avoid boxing overhead.
30

Write global exception handling for a REST API in Spring Boot.

Spring BootMedium
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@RestControllerAdvice public class GlobalExceptionHandler { @ExceptionHandler(ResourceNotFoundException.class) public ProblemDetail handleNotFound(ResourceNotFoundException ex) { return ProblemDetail.forStatusAndDetail(HttpStatus.NOT_FOUND, ex.getMessage()); } @ExceptionHandler(MethodArgumentNotValidException.class) public ProblemDetail handleValidation(MethodArgumentNotValidException ex) { ProblemDetail pd = ProblemDetail.forStatus(HttpStatus.BAD_REQUEST); pd.setProperty("errors", ex.getBindingResult().getFieldErrors() .stream().map(e -> e.getField() + ": " + e.getDefaultMessage()).toList()); return pd; } }
31

Count the frequency of each word in a sentence.

Collections and StreamsMedium
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String text = "java is fun and java is fast"; Map<String, Long> freq = Arrays.stream(text.toLowerCase().split("\\s+")) .collect(Collectors.groupingBy( Function.identity(), LinkedHashMap::new, Collectors.counting())); System.out.println(freq); // {java=2, is=2, fun=1, and=1, fast=1}
32

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.
33

Write a reusable useFetch custom hook.

React FrontendMedium
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export function useFetch(url) { const [state, setState] = useState({ data: null, loading: true, error: null }); useEffect(() => { let ignore = false; setState(s => ({ ...s, loading: true })); fetch(url) .then(r => r.ok ? r.json() : Promise.reject(new Error(r.statusText))) .then(data => { if (!ignore) setState({ data, loading: false, error: null }); }) .catch(error => { if (!ignore) setState({ data: null, loading: false, error }); }); return () => { ignore = true; }; }, [url]); return state; } // Usage: const { data, loading, error } = useFetch(`/api/orders/${id}`);
34

Write a basic CRUD REST controller in Spring Boot.

REST APIs, Security and MicroservicesEasy
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@RestController @RequestMapping("/api/products") public class ProductController { private final ProductService service; public ProductController(ProductService service) { this.service = service; } @GetMapping("/{id}") public ProductDto get(@PathVariable Long id) { return service.get(id); } @PostMapping public ResponseEntity<ProductDto> create(@Valid @RequestBody ProductRequest req) { ProductDto saved = service.create(req); return ResponseEntity.created(URI.create("/api/products/" + saved.id())).body(saved); } @DeleteMapping("/{id}") @ResponseStatus(HttpStatus.NO_CONTENT) public void delete(@PathVariable Long id) { service.delete(id); } }
35

Returning an entity from a REST API causes infinite recursion in JSON. Why, and how do you fix it?

JPA and HibernateMedium
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Bidirectional relationships, such as Order having items and each item referencing its order, make Jackson serialise back and forth endlessly, leading to StackOverflowError. The cleanest fix is to return DTOs instead of entities, so you control exactly what is exposed. Quick fixes include @JsonManagedReference with @JsonBackReference or @JsonIgnore on one side. DTOs also stop lazy loading during serialisation and avoid leaking internal fields.
36

Explain the common HTTP status codes a REST API should return.

REST APIs, Security and MicroservicesEasy
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200 OK for successful reads and updates, 201 Created with a Location header after creating a resource, and 204 No Content for successful deletes. 400 Bad Request for validation errors, 401 Unauthorized when authentication is missing or invalid, 403 Forbidden when the user is authenticated but not allowed, 404 Not Found, 409 Conflict for version or duplicate conflicts, and 429 Too Many Requests for rate limits. 500 means an unexpected server error and 503 means temporarily unavailable.

Companies with offices in Noida (6)

IT services

HCLTech

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Noida, Chennai, Bengaluru +2

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IT services

Tech Mahindra

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Pune, Hyderabad, Bengaluru +2

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Product

Oracle

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Hyderabad, Noida +2

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Banking & finance

Barclays

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Pune, Chennai, Noida +1

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Fintech

Paytm

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Noida, Bengaluru, Mumbai

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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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Frequently asked questions

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

Companies with large offices in Noida include HCLTech, Tech Mahindra, Oracle, Barclays, Paytm, Publicis Sapient. Use their company pages below to practise employer-specific sets.

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

The questions depend more on the company than the city. Noida's mix of employers decides the style: Freshers often find their first role here, and many teams run hybrid work

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

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

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