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Java Full Stack with React Interview Questions in Hyderabad

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

Java Full Stack with React jobs in Hyderabad

Hyderabad has large engineering and capability centres of global technology, banking and pharma companies around HITEC City and the Financial District. Many roles are with global capability centres that work with teams in the US and Europe.

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

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01

A security review found a login query built by string concatenation. What is the risk and the fix?

SQL and DatabasesEasy
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Concatenating user input into SQL allows SQL injection, where input like ' OR '1'='1 changes the query and can bypass login or dump data. Use parameterised queries: PreparedStatement with ? placeholders, Spring Data method queries, or @Query with named parameters, which send values separately from the SQL. Also validate input, use a database user with least privilege and never show raw SQL errors to users.
02

How does JWT-based authentication work?

REST APIs, Security and MicroservicesMedium
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After a successful login, the server issues a JSON Web Token containing a header, a payload of claims such as user ID, roles and expiry, and a signature made with a secret or private key. The client sends it in the Authorization: Bearer header with each request. The server verifies the signature and expiry without a session lookup, which suits stateless APIs. Keep access tokens short-lived, do not store sensitive data in the payload because it is only encoded, and use refresh tokens for renewal.
03

What is the difference between lazy and eager fetching?

JPA and HibernateMedium
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Lazy fetching loads an association only when it is first accessed, using a proxy. Eager fetching loads it immediately with the parent. By default, @OneToMany and @ManyToMany are lazy, while @ManyToOne and @OneToOne are eager. Best practice is to make all associations lazy and fetch what each use case needs with JOIN FETCH or entity graphs, because eager loading often pulls large object graphs and causes extra queries.
04

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.
05

Why is constructor injection preferred over field injection?

Spring BootMedium
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Constructor injection makes dependencies explicit and lets fields be final, so the object is always fully initialised and immutable. It allows plain unit tests without Spring or reflection, because you can pass mocks to the constructor. A long constructor also signals that a class has too many responsibilities. Field injection with @Autowired hides dependencies and needs a container or reflection in tests. With a single constructor, @Autowired is not even needed.
06

A search query that used to take milliseconds now takes 10 seconds as data grew. How do you troubleshoot?

SQL and DatabasesMedium
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Get the exact SQL from logs or the slow query log and run EXPLAIN ANALYZE to see whether it does a full scan, a bad join order or a big sort. Check for missing or unused indexes, functions on indexed columns, implicit type conversions and outdated statistics. Add the right composite index, rewrite the query, select fewer columns and paginate. For text search, use a full-text index or a search engine instead of LIKE '%term%'.
07

After calling setCount(count + 1), console.log(count) still shows the old value. Why?

React FrontendMedium
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State updates are scheduled, not applied immediately. The count variable in the current render is a constant snapshot, so logging right after setState shows the old value; the new value appears in the next render. React also batches multiple updates. When the next state depends on the previous one, use the updater form setCount(c => c + 1), which works correctly even when called several times. Use useEffect to react to the updated value.
08

Your application fails at startup with a circular dependency error between two services. What do you do?

Spring BootMedium
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Spring Boot 2.6 and later forbid circular references by default. The real fix is design: two services depending on each other usually means a responsibility is in the wrong place. Extract the shared logic into a third bean, or use an application event so one service notifies the other without a direct reference. Using @Lazy or allowing circular references in properties hides the problem and should only be a temporary workaround.
09

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.
10

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.
11

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.
12

How does HashMap work internally?

Collections and StreamsMedium
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HashMap stores entries in an array of buckets. The key's hashCode is spread and masked to find a bucket index. Collisions are kept in a linked list, and since Java 8 a bucket converts to a red-black tree after 8 entries when capacity is at least 64, giving O(log n) worst case. When size exceeds capacity times load factor 0.75, the table doubles and entries are redistributed. get uses hashCode to find the bucket and equals to find the key.
13

Describe a time you improved the performance of an application.

JPA and HibernateHard
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Situation: our dashboard API took eight seconds and users complained. Task: I was asked to bring it under one second. Action: using SQL logs and a profiler, I found N+1 queries and a missing index. I rewrote the query with a DTO projection, added a composite index and cached reference data with a short expiry. Result: response time dropped to about 400 milliseconds, and I added the query-count check to our test suite.
14

Use map, filter and reduce to get the total value of in-stock products.

JavaScript, HTML and CSSEasy
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const products = [ { name: 'Pen', price: 20, qty: 10, inStock: true }, { name: 'Bag', price: 900, qty: 0, inStock: false }, { name: 'Book', price: 250, qty: 4, inStock: true }, ]; const total = products .filter(p => p.inStock) .map(p => p.price * p.qty) .reduce((sum, value) => sum + value, 0); console.log(total); // 1200
15

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.
16

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. */
17

The application fails with NoSuchBeanDefinitionException for a service. How do you debug it?

Spring BootEasy
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Check that the class has @Service or @Component, or is created by a @Bean method. Make sure it is inside the package of the main @SpringBootApplication class or a scanned sub-package. If there are several implementations, use @Qualifier or @Primary. Also check @Profile or @Conditional annotations that may disable it in the current environment. Running with --debug prints the condition report that shows why a bean was not created.
18

What are window functions and how are they different from GROUP BY?

SQL and DatabasesMedium
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Window functions compute a value over a set of related rows while keeping every row in the result, unlike GROUP BY which collapses rows into one per group. They use the OVER clause with optional PARTITION BY and ORDER BY. Examples are ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD and running SUM. For instance, you can show each employee with their department's average salary in the same row.
19

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.
20

How does the useEffect dependency array work?

React FrontendMedium
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useEffect runs after the component renders. With no dependency array it runs after every render, with an empty array it runs once after mount, and with values like [userId] it runs again whenever those values change. Return a cleanup function to cancel subscriptions, timers or requests before the next run or on unmount. Missing dependencies cause stale data, so follow the exhaustive-deps lint rule. Effects are for syncing with external systems, not for computing derived values.
21

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.
22

What roles do an API gateway and service discovery play in microservices?

REST APIs, Security and MicroservicesMedium
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An API gateway, such as Spring Cloud Gateway, is the single entry point for clients. It handles routing, authentication, rate limiting, CORS and request logging. Service discovery lets services find each other without hard-coded addresses: with Eureka or Consul, services register themselves, and clients look them up. On Kubernetes, built-in Services and DNS usually replace a separate discovery server, and an ingress or gateway handles external traffic.
23

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.
24

Sort a list of products by category, then by price descending, then by name.

Collections and StreamsMedium
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products.sort( Comparator.comparing(Product::getCategory) .thenComparing(Product::getPrice, Comparator.reverseOrder()) .thenComparing(Product::getName)); // Null-safe variant for an optional field: Comparator<Product> byBrand = Comparator.comparing( Product::getBrand, Comparator.nullsLast(Comparator.naturalOrder()));
25

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.
26

Write a controller slice test with @WebMvcTest and MockMvc.

Spring BootHard
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@WebMvcTest(ProductController.class) class ProductControllerTest { @Autowired MockMvc mvc; @MockitoBean ProductService service; // @MockBean before Boot 3.4 @Test void returnsProduct() throws Exception { when(service.getProduct(1L)).thenReturn(new ProductDto(1L, "Pen", 20.0)); mvc.perform(get("/api/products/1")) .andExpect(status().isOk()) .andExpect(jsonPath("$.name").value("Pen")); } }
27

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.
28

Find the second highest salary from a list of employees using streams.

Collections and StreamsMedium
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Optional<Double> second = employees.stream() .map(Employee::getSalary) .distinct() .sorted(Comparator.reverseOrder()) .skip(1) .findFirst(); second.ifPresentOrElse( s -> System.out.println("Second highest: " + s), () -> System.out.println("Not enough distinct salaries")); // distinct() handles ties at the top salary.
29

What is CORS and how do you configure it for a React frontend?

REST APIs, Security and MicroservicesMedium
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CORS is a browser rule that blocks JavaScript from calling a different origin unless the server allows it with response headers like Access-Control-Allow-Origin. A React app on localhost:5173 calling an API on localhost:8080 is cross-origin. In Spring, define a CorsConfigurationSource bean with the allowed origins, methods and headers, and enable http.cors() in the security chain so preflight OPTIONS requests pass. Never use a wildcard origin together with credentials.
30

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.
31

What are the entity lifecycle states in JPA?

JPA and HibernateMedium
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A new or transient entity is just a Java object not known to the persistence context. A managed entity is attached to the context; changes are tracked and flushed automatically through dirty checking. A detached entity was managed but the context has closed, so changes are not tracked unless you merge it. A removed entity is scheduled for deletion on flush. Understanding these states explains why setters inside a transaction update the database without calling save.
32

Implement a cart counter using useReducer.

React FrontendEasy
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function cartReducer(state, action) { switch (action.type) { case 'add': return { count: state.count + 1 }; case 'remove': return { count: Math.max(0, state.count - 1) }; case 'reset': return { count: 0 }; default: throw new Error('Unknown action ' + action.type); } } function Cart() { const [state, dispatch] = useReducer(cartReducer, { count: 0 }); return ( <div> <span>Items: {state.count}</span> <button onClick={() => dispatch({ type: 'add' })}>+</button> <button onClick={() => dispatch({ type: 'remove' })}>-</button> </div> ); }
33

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.
34

Explain the JavaScript event loop, including microtasks and macrotasks.

JavaScript, HTML and CSSHard
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JavaScript runs on a single thread with a call stack. Asynchronous work is handled by the browser or Node, and callbacks wait in queues. After the stack empties, the event loop runs all microtasks first, such as promise callbacks and queueMicrotask, then one macrotask, such as setTimeout or an I/O callback, then renders if needed. So Promise.resolve().then(a) runs before setTimeout(b, 0). Long synchronous code blocks everything, including UI updates.
35

Why is String immutable in Java?

Core JavaEasy
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Once created, a String object cannot change. This allows the String pool to safely share literals, makes strings thread-safe without locking, lets hashCode be cached for fast HashMap keys, and protects security-sensitive values like file paths, class names and URLs from being changed after validation. Any operation such as concat or replace returns a new String, which is why heavy modification should use StringBuilder.
36

Create a scheduled job that runs every night at 2 AM in Spring Boot.

Spring BootEasy
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@SpringBootApplication @EnableScheduling public class App { } @Component public class CleanupJob { private final SessionRepository repo; public CleanupJob(SessionRepository repo) { this.repo = repo; } @Scheduled(cron = "0 0 2 * * *", zone = "Asia/Kolkata") public void removeExpiredSessions() { repo.deleteByExpiresAtBefore(Instant.now()); } } // With several instances, use ShedLock so only one runs the job.

Companies with offices in Hyderabad (15)

IT services

TCS

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Mumbai, Chennai, Pune +2

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IT services

Infosys

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Mysuru, Pune +2

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IT services

Wipro

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Hyderabad, Pune +2

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Consulting

Accenture

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Hyderabad, Pune +2

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IT services

Cognizant

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Chennai, Bengaluru, Pune +2

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IT services

Capgemini

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Mumbai, Bengaluru, Pune +2

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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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IT services

LTIMindtree

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Mumbai, Pune, Bengaluru +2

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IT services

Persistent Systems

Java Full Stack with React interview questions

  • 30 questions
  • 4 rounds

Pune, Nagpur, 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

JP Morgan Chase

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Mumbai, Bengaluru, Hyderabad

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Banking & finance

Goldman Sachs

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Hyderabad, Mumbai

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E-commerce & consumer tech

Flipkart

Java Full Stack with React interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Hyderabad

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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 Hyderabad?

Companies with large offices in Hyderabad include TCS, Infosys, Wipro, Accenture, Cognizant, Capgemini, HCLTech, Tech Mahindra, LTIMindtree, Persistent Systems. Use their company pages below to practise employer-specific sets.

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

The questions depend more on the company than the city. Hyderabad's mix of employers decides the style: Many roles are with global capability centres that work with teams in the US and Europe

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

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

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