Java Full Stack with React Interview Questions in Indore
36 practice questions with answers for Java Full Stack with React interviews in Indore.
Java Full Stack with React jobs in Indore
Indore is one of central India's fastest-growing IT hubs, with IT-services campuses and product start-ups in its Super Corridor and IT parks. Companies here hire many freshers and value hands-on project work.
Below are 36 questions that match the mix of service, product and domain employers hiring java full stack developers in Indore.
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01
Write CSS for a product grid that shows 1 column on mobile, 2 on tablet and 4 on desktop.
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.
03
What are the correct and incorrect ways to use Optional?
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.
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.
05
Fetch a list of products from an API and show loading and error states.
It happens when one query loads N parent rows and then each lazy association fires a separate query, giving N+1 queries. For example, listing 100 orders and calling getCustomer on each. Solve it with JOIN FETCH in JPQL, @EntityGraph on the repository method, batch fetching with hibernate.default_batch_fetch_size, or DTO projections that select only the needed columns. Enable SQL logging or a statistics tool in development to catch it early.
07
Your code has frequent NullPointerExceptions from repository lookups. How would you redesign it?
Return Optional from lookup methods so callers must handle the missing case, for example findById(id).orElseThrow(). Validate inputs at the API boundary with Bean Validation, initialise collections to empty lists instead of null and use Objects.requireNonNull in constructors. Java 17 helpful NPE messages show which variable was null, which speeds debugging. Do not use Optional for fields or method parameters; it is meant for return values.
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
The application fails with NoSuchBeanDefinitionException for a service. How do you debug it?
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.
10
Explain the database design of a project you have worked on.
In my e-commerce project I designed tables for users, addresses, products, categories, orders, order_items and payments. Orders had a foreign key to users, and order_items linked orders and products with quantity and price at purchase time, so later price changes did not affect old orders. I added unique constraints on email and SKU, indexes on order status and date, and used Flyway for version-controlled changes.
11
How do you store user passwords securely in Spring Boot? Show the code.
@Bean
PasswordEncoder passwordEncoder() {
return new BCryptPasswordEncoder(12);
}
public void register(RegisterRequest req) {
User user = new User(req.email(), encoder.encode(req.password()));
userRepository.save(user);
}
public boolean checkLogin(String raw, User user) {
return encoder.matches(raw, user.getPasswordHash());
}
// BCrypt adds a random salt and is deliberately slow.
// Never store plain text or use MD5/SHA-1 for passwords.
12
Database passwords and API keys are committed in application.properties. How do you fix this?
Remove the secrets from the repository, rotate the exposed credentials immediately, and clean the history if needed. Replace values with placeholders such as ${DB_PASSWORD} and supply them through environment variables, Kubernetes Secrets or a vault like HashiCorp Vault or a cloud secrets manager. Add a pre-commit secret scanner, keep local values in an ignored file, and give each environment its own credentials with least privilege.
13
Find the top 3 highest-paid employees in each department.
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.
14
Bind custom properties from application.yml into a type-safe class.
Actuator adds production-ready endpoints for monitoring and management, such as /actuator/health, /actuator/info, /actuator/metrics and /actuator/prometheus. Kubernetes uses health liveness and readiness groups for probes. Metrics are collected through Micrometer and can be exported to Prometheus, Datadog or other systems. Only expose the endpoints you need with management.endpoints.web.exposure.include and secure them, because endpoints like env or heapdump can leak sensitive data.
16
What is the difference between persist and merge, and between save and saveAndFlush?
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.
17
Write a repository query that loads orders with their items in one query.
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);
}
I built a job portal using React with Vite, Spring Boot 3, Spring Security with JWT and MySQL. Recruiters could post jobs and candidates could apply and track status. I designed the REST APIs, implemented role-based access, added pagination and search, and used TanStack Query on the frontend. I deployed it with Docker and a CI pipeline. The hardest part was file upload for resumes, which I solved with pre-signed object storage URLs.
20
Where should a React app store the JWT, and what are the trade-offs?
localStorage is simple but any XSS script can read it. In-memory storage is safer but is lost on refresh. The commonly recommended pattern is a short-lived access token kept in memory and a refresh token in an HttpOnly, Secure, SameSite cookie that JavaScript cannot read, used to get new access tokens. Cookies need CSRF protection for state-changing calls. Whatever you choose, prevent XSS with proper escaping and a Content Security Policy.
21
Write code that runs tasks in parallel using ExecutorService and collects results.
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.
23
How does the this keyword work, and how do arrow functions change it?
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.
Events bubble up from the target element to its ancestors. With event delegation you attach one listener to a parent, such as a ul, and use event.target.closest('li') to find which child was clicked. This saves memory compared with a listener on every item and automatically works for items added later. It is commonly used for dynamic tables and lists. React uses a similar idea by attaching listeners at the root.
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.
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.
27
Write a record and use pattern matching in a switch expression.
I agree on the API contract first using an OpenAPI spec or Swagger UI, so frontend and QA can start in parallel with mock data. I share example requests and error responses, and I tell the team early if a field must change. For example, in my last sprint I gave QA a Postman collection with test cases for every endpoint. This reduced back-and-forth and our feature passed testing on the first cycle.
29
Which features from Java 17 and Java 21 are useful for a full stack developer?
Java 17 brought records for immutable data carriers, sealed classes to restrict inheritance, text blocks for multi-line JSON or SQL, and pattern matching for instanceof. Java 21, the current widely used LTS alongside 17, added virtual threads for cheap blocking concurrency, pattern matching for switch, record patterns and sequenced collections. Spring Boot 3 needs Java 17 or later, and from Boot 3.2 virtual threads can be enabled with one property.
30
Why does React need a key prop when rendering lists?
Keys help React match list items between renders, so it knows which items were added, removed or moved. Use a stable unique ID from the data, such as product.id. Using the array index as key causes bugs when items are reordered or deleted, because state and input values can attach to the wrong row. Keys only need to be unique among siblings, and they are not passed to the component as a prop.
31
How do profiles and application.yml work in Spring Boot?
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.
32
What is the difference between controlled and uncontrolled components?
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.
33
What is CORS and how do you configure it for a React frontend?
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.
34
In a search box, older API responses sometimes overwrite newer results. How do you fix this race condition?
Each keystroke starts a request, and responses can arrive out of order. Debounce the input by about 300 milliseconds so fewer requests are sent. In the effect, cancel the previous request with AbortController in the cleanup function, or keep an ignore flag so stale responses are discarded. Libraries like TanStack Query handle this automatically by keying queries on the search term and ignoring outdated results.
35
How do indexes improve performance, and when can they hurt?
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
In a bidirectional @OneToMany relationship, what does mappedBy mean?
mappedBy marks the inverse side and names the field on the other entity that owns the relationship. The owning side, usually the @ManyToOne with the foreign key column, is the one Hibernate uses to write the join column. For example, Order has @OneToMany(mappedBy = "order") and OrderItem has @ManyToOne @JoinColumn(name = "order_id"). Always update both sides in helper methods such as addItem to keep the object graph consistent.
Few big employers listed in Indore?
Many Indore candidates also apply to teams in Pune and to remote or hybrid roles. Practise the Pune set as well.
Which companies hire Java Full Stack with React professionals in Indore?
Companies with large offices in Indore include many IT services and product firms. Use their company pages below to practise employer-specific sets.
Are Java Full Stack with React interviews in Indore different from other cities?
The questions depend more on the company than the city. Indore's mix of employers decides the style: Companies here hire many freshers and value hands-on project work
How do I find Java Full Stack with React jobs in Indore?
Shortlist companies with Indore offices, keep your CV focused on Java Full Stack with React projects, apply on company career pages and job portals with the Indore filter, and practise the questions on this page before each interview.