Infosys Java Full Stack with React Interview Questions & Answers
Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About Infosys hiring for Java Full Stack with React roles
Infosys is an Indian multinational IT services and consulting company offering digital transformation, cloud, application management, testing and data services to global clients. It is known for its Mysuru training campus where new hires go through foundation programmes. In India it recruits for roles such as systems engineer, test engineer, data analyst and data engineer, often through campus and off-campus drives.
For Java Full Stack with React roles, this Infosys practice set focuses most on Core Java (6), Spring Boot (5), JavaScript, HTML and CSS (5), SQL and Databases (4). It has 16 easy, 14 medium questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Bengaluru, India
Main India offices
Bengaluru, Mysuru, Pune, Hyderabad, Chennai
Infosys Java Full Stack with React interview process
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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01
Create a scheduled job that runs every night at 2 AM in Spring Boot.
@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.
02
You are designing a new feature. When would you choose a relational database and when a NoSQL database?
Choose a relational database like PostgreSQL or MySQL when data is structured, relationships matter and you need transactions and joins, such as orders, payments and inventory. Choose NoSQL when you need a flexible schema or huge horizontal scale for simple access patterns: MongoDB for documents, Redis for caching and sessions, Cassandra for high-write time series and Elasticsearch for search. Many systems use both, with SQL as the source of truth.
String is immutable, so every change creates a new object. StringBuilder is mutable and fast but not thread-safe, which makes it the default choice for building strings inside a method or loop. StringBuffer is mutable and synchronized, so it is thread-safe but slower, and it is rarely needed today because strings are seldom shared across threads while being built. The compiler already uses optimized concatenation for simple + expressions outside loops.
Atomicity means a transaction fully succeeds or fully rolls back. Consistency means it moves the database from one valid state to another, respecting constraints. Isolation means concurrent transactions do not see each other's partial work. Durability means committed data survives crashes, thanks to write-ahead logs. A bank transfer that debits one account and credits another is the classic example where all four properties matter.
05
What is the difference between == and equals() in Java?
The == operator compares references for objects, meaning it checks whether two variables point to the same object in memory. equals() compares logical content when a class overrides it, as String, Integer and most collections do. For example, new String("a") == new String("a") is false but equals() returns true. For primitives, == compares values. Always use equals() for objects and Objects.equals(a, b) to stay null-safe.
REST treats everything as a resource identified by a URL, such as /api/orders/42, and uses standard HTTP methods to act on it. Requests are stateless, so each one carries all the information needed, including the auth token. Responses use proper status codes and representations, usually JSON, and can be cacheable. Good REST design uses nouns in URLs, plural resource names, nested paths for relations and query parameters for filtering and pagination.
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.
09
Compare monolithic and microservices architecture.
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.
10
How do you take feedback from a senior on your React code?
Situation: in my first month, a senior reviewer left many comments about large components and duplicated fetch logic. Task: improve the code and learn from it. Action: I thanked him, asked for a short call to understand the reasoning, split the component, and wrote a custom hook for data fetching. Result: the pull request was approved, and the hook was reused in three other screens. I now self-review using his checklist.
During compilation, declarations are moved to the top of their scope. Function declarations are hoisted fully, so they can be called before they appear. var declarations are hoisted and initialised to undefined. let, const and class declarations are hoisted but stay uninitialised in the temporal dead zone, so accessing them early throws a ReferenceError. Function expressions assigned to variables follow the variable's rules.
It is a convenience annotation combining three annotations. @SpringBootConfiguration marks the class as a configuration source. @EnableAutoConfiguration tells Boot to configure beans based on the classpath and properties, for example a DataSource when a JDBC driver is present. @ComponentScan scans the package of the main class and its sub-packages for components. That is why the main class should sit in the root package of your project.
13
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.
14
Write a query to find duplicate email addresses in a users table and delete the extra rows.
-- Find duplicates
SELECT email, COUNT(*) AS cnt
FROM users
GROUP BY email
HAVING COUNT(*) > 1;
-- Keep the lowest id, delete the rest (MySQL / PostgreSQL)
DELETE FROM users u
USING users k
WHERE u.email = k.email
AND u.id > k.id; -- PostgreSQL syntax
-- Then add: ALTER TABLE users ADD CONSTRAINT ux_email UNIQUE (email);
15
Tell me about a time you delivered a feature under a tight deadline.
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.
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.
17
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.
18
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.
19
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.
20
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.
21
What is the difference between checked and unchecked exceptions?
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.
22
Write CSS for a product grid that shows 1 column on mobile, 2 on tablet and 4 on desktop.
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
What is the difference between authentication and authorization?
Authentication verifies who the user is, for example by checking a password, OTP or token. Authorization decides what that authenticated user is allowed to do, for example only admins can delete products. In Spring Security, authentication produces an Authentication object with granted authorities, and authorization uses those authorities in URL rules or annotations like @PreAuthorize("hasRole('ADMIN')"). A failed authentication gives 401 and a failed authorization gives 403.
25
Write a query that shows daily sales with a running total for the month.
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;
26
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.
27
What is a closure in JavaScript? Give a practical use.
A closure is a function that remembers variables from the scope where it was created, even after that outer function has returned. For example, function counter() { let n = 0; return () => ++n; } returns a function that keeps its own private n. Closures are used for data privacy, function factories, event handlers, debounce and memoization, and React hooks rely on them. Stale closures in effects are a common bug when dependencies are missing.
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.
29
Explain the difference between map and flatMap in streams.
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.
30
What causes LazyInitializationException and how do you fix it properly?
It occurs when a lazy association is accessed after the persistence context has closed, for example in a controller or during JSON serialisation outside the transaction. The proper fix is to fetch the data inside the service transaction using JOIN FETCH or @EntityGraph and map it to a DTO. Avoid enabling spring.jpa.open-in-view as a crutch, and avoid switching associations to eager, because both hide performance problems.
Tips to crack the Infosys Java Full Stack with React interview
Practise pseudocode output questions and puzzle-style reasoning, which commonly appear in Infosys online tests and HackWithInfy style contests.
Revise SQL joins, normalisation and one programming language well enough to write and explain simple programs on paper.
Mention willingness to learn new technologies and relocate, since Infosys emphasises its training programme and flexible project allocation.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; Infosys interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the Infosys Java Full Stack with React interview?
Candidates usually go through 4 stages: Online assessment (aptitude, reasoning + pseudocode); Coding test; Technical interview; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the Infosys Java Full Stack with React interview?
This practice set leans on Core Java (6), Spring Boot (5), JavaScript, HTML and CSS (5), SQL and Databases (4). Revise those first, then practise explaining one or two of your own projects end to end, because most Infosys interviewers ask you to walk through real work.
Are these the exact questions asked at Infosys?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like Infosys's. They are not a leaked or verified list of past questions.
Where does Infosys hire Java Full Stack with React professionals in India?
Infosys has large teams in Bengaluru, Mysuru, Pune, Hyderabad, Chennai. Openings and locations change often, so check the Infosys careers page and filter by city and experience.
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