Skip to content
Java
All coursesPlacement Report
‹ Back to previous sectionCourse homeAll page URLs

Java Interview Questions in Noida

36 practice questions with answers for Java interviews in Noida.

Java 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 developers in Noida.

Solved for NoidaStart practicing
3 QUESTIONS FREESign up to unlock the full question bank and track your progress.Unlock every question and answer, then continue practising company-wise and package-wise.
3 questions free Unlock the rest in seconds
01

Explain the SOLID principles briefly.

OOP in JavaMedium
Save to ▾
Show answer
Single Responsibility: a class has one reason to change. Open/Closed: open for extension, closed for modification. Liskov Substitution: subclasses must work wherever the parent is expected. Interface Segregation: prefer small, focused interfaces. Dependency Inversion: depend on abstractions, not concrete classes. Spring dependency injection is a practical example of dependency inversion.
02

What are method references? Give the four types.

Java 8+ Features and StreamsEasy
Save to ▾
Show answer
Method references are short forms of lambdas that just call an existing method. Types: static method (Integer::parseInt), instance method of a specific object (System.out::println), instance method of an arbitrary object of a type (String::toUpperCase) and constructor (ArrayList::new). They make stream code clearer when the lambda only forwards its arguments.
03

Your REST API returns stack traces to clients when errors happen. How do you design proper error handling?

Strings and Exception HandlingMedium
Save to ▾
Show answer
Never expose stack traces; they leak internals. In Spring Boot use a @RestControllerAdvice with @ExceptionHandler methods that map domain exceptions to status codes, such as 404 for not found and 400 for validation. Return a consistent body, ideally RFC 7807 ProblemDetail, with a code, message and trace id. Log full details on the server with the same trace id.
04

What is the difference between checked and unchecked exceptions?

Strings and Exception HandlingEasy
Save to ▾
Show answer
Checked exceptions extend Exception (but not RuntimeException) and must be caught or declared with throws, for example IOException and SQLException. Unchecked exceptions extend RuntimeException, such as NullPointerException and IllegalArgumentException, and need no declaration. Use checked exceptions for recoverable conditions callers must handle and unchecked ones for programming errors. Errors like OutOfMemoryError should not be caught.
05

What is the difference between reduce() and collect()?

Java 8+ Features and StreamsHard
Save to ▾
Show answer
reduce() combines elements into a single immutable value using an identity and an associative function, such as summing numbers. collect() is a mutable reduction that accumulates into a container like a List, Map or StringBuilder, which is far more efficient for building collections. Using reduce to build a list creates many intermediate copies, so use collect for containers.
06

What are records in Java and when should you use them?

OOP in JavaMedium
Save to ▾
Show answer
Records, final in Java 16, are concise classes for immutable data. record Point(int x, int y) {} generates private final fields, a canonical constructor, accessors, equals(), hashCode() and toString(). You can add validation in a compact constructor and add methods. Use them for DTOs, API responses and map keys. They cannot extend another class and are not suited to JPA entities, which need mutability.
07

What is the difference between ArrayList and LinkedList?

Collections FrameworkEasy
Save to ▾
Show answer
ArrayList is backed by a resizable array, so get(i) is O(1) and appends are amortised O(1), but inserting in the middle shifts elements. LinkedList is a doubly linked list with O(n) random access but O(1) add or remove at the ends or through an iterator. In practice ArrayList is faster for almost all cases because of better CPU cache use; use ArrayDeque for queues.
08

What is the difference between HashMap and ConcurrentHashMap?

Collections FrameworkMedium
Save to ▾
Show answer
HashMap is not thread safe; concurrent writes can lose data or corrupt the structure. ConcurrentHashMap supports full concurrency: reads are lock free and writes use CAS or lock a single bin, so threads rarely block each other. It does not allow null keys or values. It also provides atomic compound operations such as computeIfAbsent and merge, which avoid check-then-act races.
09

Implement the Builder pattern for a User class with many optional fields.

OOP in JavaMedium
Save to ▾
Show answer
A builder avoids long constructors. public class User { private final String name; private final int age; private User(Builder b) { name = b.name; age = b.age; } public static class Builder { private String name; private int age; public Builder name(String n) { name = n; return this; } public Builder age(int a) { age = a; return this; } public User build() { return new User(this); } } } Usage: new User.Builder().name("Asha").age(25).build(). Lombok @Builder generates this.
10

What is the role of the JIT compiler?

Java Basics and JVMMedium
Save to ▾
Show answer
The JVM first interprets bytecode, then profiles which methods run often. The Just In Time compiler converts these hot methods into optimised native code at runtime. HotSpot uses tiered compilation: C1 compiles quickly with light optimisation and C2 applies aggressive optimisations like inlining and escape analysis. This is why Java apps get faster after a warm-up period.
11

What is autoboxing and what pitfall can it cause?

Java Basics and JVMMedium
Save to ▾
Show answer
Autoboxing is automatic conversion between a primitive and its wrapper, such as int to Integer, and unboxing is the reverse. A common pitfall is a NullPointerException when unboxing a null Integer. Another is comparing Integer objects with ==, which works only for cached values from -128 to 127. Boxing inside tight loops also creates extra garbage and slows code.
12

Find the first non-repeating character in a string.

Strings and Exception HandlingMedium
Save to ▾
Show answer
Count in one pass, then scan again in order. public static char firstUnique(String s) { int[] cnt = new int[128]; for (char c : s.toCharArray()) cnt[c]++; for (char c : s.toCharArray()) { if (cnt[c] == 1) return c; } return '_'; } Two passes, O(n) time and O(1) extra space for ASCII input.
13

Clients report duplicate orders when they retry after a timeout. How do you prevent it?

Spring Boot and MicroservicesMedium
Save to ▾
Show answer
Make the create order API idempotent. The client sends an Idempotency-Key header; the server stores the key with the result in a table with a unique constraint or in Redis. A retry with the same key returns the saved response instead of creating a new order. Database unique constraints on business keys add another safety net.
14

Tell me about a time you made a codebase more readable.

Java 8+ Features and StreamsMedium
Save to ▾
Show answer
Situation: our reporting module had nested loops 200 lines long that new joiners feared. Task: make it maintainable without changing output. Action: I added snapshot tests on real report files, then refactored into small methods using streams, groupingBy and records for intermediate data, and reviewed each step with a teammate. Result: the module shrank by 40 percent and later changes took a day instead of a week.
15

Bind typed configuration properties with validation in Spring Boot.

Spring Boot and MicroservicesMedium
Save to ▾
Show answer
Use a record with @ConfigurationProperties. @ConfigurationProperties(prefix = "payment") @Validated public record PaymentProps( @NotBlank String baseUrl, @Min(100) int timeoutMs) {} // application.yml // payment: // base-url: https://pay.internal // timeout-ms: 2000 Enable it with @ConfigurationPropertiesScan on the main class. The app fails at startup if values are invalid.
16

Describe a time you improved the design of existing code.

OOP in JavaMedium
Save to ▾
Show answer
Situation: our notification module used a 400 line class with switch cases for email, SMS and WhatsApp. Task: add push notifications without breaking anything. Action: I wrote tests for current behaviour, extracted a Notifier interface with one class per channel and used Spring to inject them by type. Result: push was added in one new class, bugs in that module dropped and new channels now take hours, not days.
17

A query is fast in development but takes 8 seconds in production. How do you investigate?

JDBC, Hibernate and JPAMedium
Save to ▾
Show answer
Production has more data, so check the execution plan with EXPLAIN ANALYZE on production-like data. Look for full table scans, missing indexes on filter or join columns, functions on indexed columns and poor statistics. Check if Hibernate generates the SQL you expect. Add a suitable composite index, rewrite the query or paginate, and verify the plan improves before release.
18

An application gets StackOverflowError in a recursive method. What do you do?

Java Basics and JVMMedium
Save to ▾
Show answer
StackOverflowError means the thread stack is full, usually because recursion has no proper base case or the input is very deep. First check the base case and the recursive step with the failing input. If recursion is correct but deep, such as walking a long linked structure, convert it to an iterative solution with an explicit stack. Raising -Xss is only a temporary workaround.
19

Explain the main memory areas of the JVM.

Java Basics and JVMMedium
Save to ▾
Show answer
The heap stores all objects and is shared by threads; it is managed by the garbage collector. Each thread has its own stack holding frames with local variables and partial results. Metaspace (native memory since Java 8) stores class metadata. There are also the program counter register and native method stacks. StackOverflowError comes from the stack and OutOfMemoryError usually from heap or metaspace.
20

What is a deadlock and how can it be prevented?

Multithreading and ConcurrencyMedium
Save to ▾
Show answer
A deadlock happens when two or more threads each hold a lock and wait for a lock held by the other, so none can continue. It needs mutual exclusion, hold and wait, no preemption and circular wait. Prevent it by always acquiring locks in the same global order, using tryLock with a timeout, holding locks briefly and avoiding calls to unknown code while holding a lock.
21

How do you make sure database changes are released safely?

JDBC, Hibernate and JPAMedium
Save to ▾
Show answer
Situation: a manual schema change once broke our staging environment. Task: make migrations reliable. Action: I introduced Flyway with versioned scripts in the repo, required backward compatible changes such as adding nullable columns first, and ran migrations in CI against a test database. Result: we had zero failed migrations over the next year and rollbacks became predictable.
22

Read a large text file line by line efficiently and count lines containing ERROR.

Strings and Exception HandlingMedium
Save to ▾
Show answer
Stream the file lazily so it never loads fully into memory. Path p = Path.of("app.log"); try (Stream<String> lines = Files.lines(p)) { long errors = lines .filter(l -> l.contains("ERROR")) .count(); System.out.println(errors); } try-with-resources closes the file handle. BufferedReader.readLine() in a loop is an equally good option.
23

Run two tasks in parallel with CompletableFuture and combine their results.

Multithreading and ConcurrencyMedium
Save to ▾
Show answer
Use a dedicated executor for I/O work. ExecutorService pool = Executors.newFixedThreadPool(4); CompletableFuture<User> user = CompletableFuture.supplyAsync(() -> userApi.get(id), pool); CompletableFuture<List<Order>> orders = CompletableFuture.supplyAsync(() -> orderApi.list(id), pool); Profile p = user.thenCombine(orders, Profile::new) .orTimeout(2, TimeUnit.SECONDS) .join();
24

Write a Kafka producer and consumer in Spring Boot.

Spring Boot and MicroservicesHard
Save to ▾
Show answer
Spring Kafka hides most boilerplate. @Service class OrderEvents { private final KafkaTemplate<String, OrderPlaced> kafka; OrderEvents(KafkaTemplate<String, OrderPlaced> k) { kafka = k; } void publish(OrderPlaced e) { kafka.send("orders", e.orderId(), e); } } @Component class OrderListener { @KafkaListener(topics = "orders", groupId = "inventory") void on(OrderPlaced e) { inventory.reserve(e); } } Using orderId as key keeps events for one order in the same partition and order.
25

How do you explain OOP concepts to a junior developer who is new to Java?

OOP in JavaEasy
Save to ▾
Show answer
Situation: I mentored two interns who struggled with OOP. Task: help them design classes for a library app. Action: I used real objects they knew, like Book and Member, showed encapsulation with private fields, then wrote one interface with two implementations to show polymorphism, and reviewed their code daily. Result: within two weeks they designed modules on their own and their pull requests needed fewer review comments.
26

What is a functional interface?

Java 8+ Features and StreamsEasy
Save to ▾
Show answer
A functional interface has exactly one abstract method, so it can be implemented with a lambda or method reference. It may also have default and static methods. Examples are Runnable, Comparator, and those in java.util.function: Function, Predicate, Consumer, Supplier and BiFunction. The @FunctionalInterface annotation makes the compiler enforce the single abstract method rule.
27

Write a Spring Data JPA repository method that fetches orders with items to avoid N+1.

JDBC, Hibernate and JPAMedium
Save to ▾
Show answer
Use JOIN FETCH or an entity graph. public interface OrderRepository extends JpaRepository<Order, Long> { @Query("select distinct o from Order o join fetch o.items where o.customerId = :cid") List<Order> findWithItems(@Param("cid") Long customerId); @EntityGraph(attributePaths = "items") List<Order> findByStatus(String status); } Both load orders and items in one query.
28

What is the N+1 select problem in Hibernate and how do you fix it?

JDBC, Hibernate and JPAMedium
Save to ▾
Show answer
N+1 happens when you load N parent entities with one query and then a lazy association triggers one extra query per parent, giving N+1 queries. Fix it with a JOIN FETCH in JPQL, an @EntityGraph on the repository method, or batch fetching with @BatchSize or hibernate.default_batch_fetch_size. Detect it by enabling SQL logging or using a query count assertion in tests.
29

What is the difference between composition and inheritance, and which should you prefer?

OOP in JavaMedium
Save to ▾
Show answer
Inheritance is an is-a relation where the subclass reuses parent code, but it creates tight coupling and fragile hierarchies. Composition is a has-a relation where a class holds another object and delegates work, such as a Car having an Engine. Prefer composition because it is flexible, allows changing behaviour at runtime and is easier to test. Use inheritance only for a true is-a relationship.
30

Explain bean scopes in Spring.

Spring Boot and MicroservicesMedium
Save to ▾
Show answer
singleton is the default: one instance per application context. prototype creates a new instance each time it is requested. Web scopes include request, session and application. Singletons must be stateless or thread safe because all requests share them. Injecting a prototype into a singleton gives only one instance, so use ObjectProvider or a scoped proxy to get fresh ones.
31

A getter returns an internal List and callers modify it, causing bugs. How do you fix this?

OOP in JavaMedium
Save to ▾
Show answer
This breaks encapsulation. Return an unmodifiable view with Collections.unmodifiableList(list) or a copy with List.copyOf(list), so callers cannot change internal state. Also copy the list passed into the constructor or setter. If the class should be fully immutable, store List.copyOf in a final field. Expose specific methods like addItem() when controlled changes are needed.
32

You need to add a new payment method to a system that has a big if-else on payment type. How would you redesign it?

OOP in JavaMedium
Save to ▾
Show answer
This breaks the Open/Closed principle. I would create a PaymentProcessor interface with a pay() method and one implementation per type, such as UpiProcessor and CardProcessor. A factory or a Spring map of beans keyed by type picks the right one. Adding a new method then means adding one new class without touching existing tested code, and each processor can be unit tested alone.
33

Code builds a large CSV report with String += inside a loop and it is very slow. Why and what is the fix?

Strings and Exception HandlingMedium
Save to ▾
Show answer
Each += creates a new String and copies all previous characters, so building n rows is O(n squared) in time and creates huge garbage. Use a single StringBuilder with append() inside the loop, ideally with an initial capacity, or write rows directly to a BufferedWriter for very large output. This turns minutes of work into milliseconds.
34

Write a minimal Dockerfile for a Spring Boot application.

Spring Boot and MicroservicesMedium
Save to ▾
Show answer
A multi-stage build keeps the image small. FROM eclipse-temurin:21-jdk AS build WORKDIR /app COPY . . RUN ./mvnw -q package -DskipTests FROM eclipse-temurin:21-jre WORKDIR /app COPY --from=build /app/target/*.jar app.jar EXPOSE 8080 ENTRYPOINT ["java", "-XX:MaxRAMPercentage=75", "-jar", "app.jar"] Spring Boot can also build images without a Dockerfile using mvn spring-boot:build-image.
35

What is the difference between start() and run()?

Multithreading and ConcurrencyEasy
Save to ▾
Show answer
start() asks the JVM to create a new thread and then calls run() on that new thread, so the code executes concurrently. Calling run() directly is just a normal method call on the current thread, so no new thread is created. Calling start() twice on the same Thread throws IllegalThreadStateException.
36

Objects used as HashMap keys cannot be found after insertion. What could be wrong?

OOP in JavaMedium
Save to ▾
Show answer
Most likely the class overrides equals() but not hashCode(), or neither, so equal keys land in different buckets. Another cause is a mutable key: a field used in hashCode() was changed after insertion, so the lookup goes to a different bucket. The fix is to implement both methods on the same fields and use immutable keys such as String, records or final classes.

Companies with offices in Noida (5)

IT services

HCLTech

Java interview questions

  • 30 questions
  • 4 rounds

Noida, Chennai, Bengaluru +2

View questions
IT services

Tech Mahindra

Java interview questions

  • 30 questions
  • 4 rounds

Pune, Hyderabad, Bengaluru +2

View questions
Product

Oracle

Java interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Hyderabad, Noida +2

View questions
Banking & finance

Barclays

Java interview questions

  • 30 questions
  • 4 rounds

Pune, Chennai, Noida +1

View questions
Fintech

Paytm

Java interview questions

  • 30 questions
  • 5 rounds

Noida, Bengaluru, Mumbai

View questions

Frequently asked questions

Which companies hire Java professionals in Noida?

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

Are Java 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 jobs in Noida?

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

Other cities

DelhiGurgaonBangaloreHyderabadPuneChennaiMumbaiKolkataAhmedabadJaipurLucknowChandigarhIndoreKochiCoimbatoreBhubaneswarNagpurVisakhapatnamThiruvananthapuram

More ways to practise

Company-wise Java questionsExperience-wise Java questionsRole-wise Java questionsCity-wise Java questionsMost asked Java questionsScenario-based questionsPractical / hands-on questionsHR & behavioural questionsJava mock interviewOnline assessment questionsTechnical round questionsManagerial round questionsJava topic sheets