Tech Mahindra 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 Tech Mahindra hiring for Java Full Stack with React roles
Tech Mahindra is an Indian IT services and consulting company and part of the Mahindra Group. It is known for its strong telecom and communications practice and also serves banking, manufacturing and healthcare clients. In India it hires for software engineers, test engineers, network engineers, data analysts and data engineers.
For Java Full Stack with React roles, this Tech Mahindra practice set focuses most on Collections and Streams (5), JavaScript, HTML and CSS (5), Core Java (4), REST APIs, Security and Microservices (4). It has 12 easy, 17 medium, 1 hard questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Pune, India
Main India offices
Pune, Hyderabad, Bengaluru, Noida, Chennai
Tech Mahindra Java Full Stack with React interview process
Online assessment (aptitude + English essay)
Coding test
Technical interview
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
Solved for Tech MahindraStart practicing
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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.
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.
05
After calling setCount(count + 1), console.log(count) still shows the old value. Why?
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.
06
How do derived query methods work in Spring Data JPA?
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.
07
Create a custom unchecked exception and throw it from a service method.
public class ResourceNotFoundException extends RuntimeException {
public ResourceNotFoundException(String message) {
super(message);
}
}
public Product getProduct(Long id) {
return repository.findById(id)
.orElseThrow(() ->
new ResourceNotFoundException("Product not found: " + id));
}
// A @RestControllerAdvice can map this exception to HTTP 404.
08
You get ConcurrentModificationException while removing items from a list inside a for-each loop. How do you fix it?
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.
09
Build a login form with basic validation in React.
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.
A clustered index defines the physical order of rows, so the table data itself is stored in the index and there can be only one. In MySQL InnoDB the primary key is the clustered index. A non-clustered or secondary index is a separate structure holding the indexed columns and a pointer, or the primary key in InnoDB, to the row. That is why a short primary key keeps every secondary index smaller.
15
What are intermediate and terminal operations in Java Streams?
Intermediate operations such as filter, map, sorted and distinct return a new stream and are lazy; nothing runs until a terminal operation is called. Terminal operations such as collect, forEach, count, reduce and findFirst trigger processing and produce a result. Laziness allows short-circuiting: with findFirst, elements are processed one by one only until a match is found. A stream can be consumed only once.
16
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.
17
What changed when moving from Spring Boot 2 to Spring Boot 3?
Spring Boot 3 requires Java 17 or later and is built on Spring Framework 6. The biggest migration task is the switch from javax.* to jakarta.* packages for persistence, validation and servlet APIs. Spring Security 6 removed WebSecurityConfigurerAdapter in favour of SecurityFilterChain beans. Boot 3 also supports GraalVM native images, Micrometer observation and tracing, and from 3.2 the RestClient and virtual thread support.
18
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.
19
Write a production-friendly Dockerfile for a Spring Boot application.
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.
21
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.
22
Find the second highest salary from a list of employees using streams.
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.
24
What is the difference between == and === in JavaScript?
== compares after type coercion, so 0 == '0' and null == undefined are true, which leads to surprising results. === compares both type and value without coercion, so 0 === '0' is false. Always use === and !== in application code. The only common exception is value == null, which checks for both null and undefined in one expression.
25
What is the difference between lazy and eager fetching?
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.
26
How does the Spring Security filter chain process a request?
Every request passes through a DelegatingFilterProxy into a FilterChainProxy, which picks the matching SecurityFilterChain. Filters run in order: CORS, CSRF, authentication filters such as BearerTokenAuthenticationFilter, exception translation and finally the authorization filter. Authentication filters build an Authentication object, validate it through the AuthenticationManager and store it in the SecurityContextHolder. The authorization filter then checks rules such as hasRole("ADMIN") before the controller runs.
27
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.
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.
29
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.
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.
Tips to crack the Tech Mahindra Java Full Stack with React interview
Read about telecom basics like 4G, 5G and network operations, since communications is Tech Mahindra's largest vertical.
Practise English essay and verbal ability sections, which often appear in Tech Mahindra online assessments.
Revise SQL and one programming language, and prepare a clear two-minute explanation of your project.
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; Tech Mahindra interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the Tech Mahindra Java Full Stack with React interview?
Candidates usually go through 4 stages: Online assessment (aptitude + English essay); 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 Tech Mahindra Java Full Stack with React interview?
This practice set leans on Collections and Streams (5), JavaScript, HTML and CSS (5), Core Java (4), REST APIs, Security and Microservices (4). Revise those first, then practise explaining one or two of your own projects end to end, because most Tech Mahindra interviewers ask you to walk through real work.
Are these the exact questions asked at Tech Mahindra?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like Tech Mahindra's. They are not a leaked or verified list of past questions.
Where does Tech Mahindra hire Java Full Stack with React professionals in India?
Tech Mahindra has large teams in Pune, Hyderabad, Bengaluru, Noida, Chennai. Openings and locations change often, so check the Tech Mahindra careers page and filter by city and experience.
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