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Java Interview Questions in Ahmedabad

36 practice questions with answers for Java interviews in Ahmedabad.

Java jobs in Ahmedabad

Ahmedabad and GIFT City have a growing market for IT services, fintech and product start-ups. Companies here value hands-on skills and the ability to work across tools, especially in smaller teams.

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

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01

What are the primitive data types in Java and their sizes?

Java Basics and JVMEasy
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Java has eight primitives: byte (1 byte), short (2), int (4), long (8), float (4), double (8), char (2 bytes, UTF-16 code unit) and boolean (true or false, size JVM dependent). Primitives store values directly and have default values when used as fields, for example 0 for int and false for boolean. Each has a wrapper class such as Integer.
02

Write code that runs 10,000 blocking tasks using virtual threads.

Multithreading and ConcurrencyMedium
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Use the virtual-thread-per-task executor in Java 21. try (var ex = Executors.newVirtualThreadPerTaskExecutor()) { for (int i = 0; i < 10_000; i++) { int id = i; ex.submit(() -> { Thread.sleep(Duration.ofMillis(200)); return id; }); } } // close() waits for all tasks All tasks finish in about 200 ms because blocked virtual threads free their carriers.
03

What is the difference between method overloading and method overriding?

OOP in JavaEasy
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Overloading means several methods in the same class share a name but differ in parameter list; it is resolved at compile time. Overriding means a subclass provides its own version of a parent method with the same signature; it is resolved at runtime through dynamic dispatch. Return type alone cannot overload a method, while overriding allows a covariant return type.
04

What is the difference between JPA, Hibernate and Spring Data JPA?

JDBC, Hibernate and JPAEasy
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JPA, now Jakarta Persistence, is a specification of interfaces and annotations for object relational mapping. Hibernate is the most popular implementation of that specification and adds its own features. Spring Data JPA sits on top and generates repository implementations from interfaces and method names like findByEmail, reducing boilerplate. Your code uses JPA annotations, Hibernate does the work and Spring Data simplifies access.
05

Does the finally block always execute?

Strings and Exception HandlingMedium
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finally runs after try and catch in almost every case, including when the try block returns or throws. It does not run if the JVM exits through System.exit(), the process is killed or the thread dies abruptly. Avoid returning from finally, because that silently overrides the try block's return value and swallows exceptions.
06

Write a Java solution for the Two Sum problem using a HashMap.

Collections FrameworkEasy
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Store each number's index and look up its complement. public int[] twoSum(int[] nums, int target) { Map<Integer, Integer> seen = new HashMap<>(); for (int i = 0; i < nums.length; i++) { Integer j = seen.get(target - nums[i]); if (j != null) return new int[]{j, i}; seen.put(nums[i], i); } return new int[0]; } One pass, O(n) time and O(n) space.
07

What is Spring Boot Actuator used for?

Spring Boot and MicroservicesMedium
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Actuator adds production endpoints such as /actuator/health for liveness and readiness probes, /actuator/metrics and /actuator/prometheus for Micrometer metrics, plus info, loggers and thread dumps. Expose only what you need with management.endpoints.web.exposure.include and secure sensitive endpoints with Spring Security. Kubernetes uses the health groups to decide restarts and traffic routing.
08

Production shows Connection is not available, request timed out after 30000ms from HikariCP. What do you check?

JDBC, Hibernate and JPAHard
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The pool is exhausted. Check for connection leaks, where code holds connections without closing, by setting leakDetectionThreshold. Look for long transactions doing remote calls inside @Transactional, slow queries holding connections and a pool size too small for the thread count. Fix leaks, move external calls outside transactions, optimise slow queries and then size the pool from load tests.
09

What are virtual threads and when should you use them?

Multithreading and ConcurrencyMedium
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Virtual threads, final in Java 21, are lightweight threads managed by the JVM and mounted on a small pool of carrier OS threads. When one blocks on I/O, it unmounts so the carrier can run another. You can run millions of them, which suits thread-per-request servers doing lots of blocking calls. They do not speed up CPU-bound work, and you should not pool them.
10

What is the difference between lazy and eager loading?

JDBC, Hibernate and JPAMedium
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Lazy loading fetches an association only when it is first accessed, using a proxy; eager loading fetches it immediately with the parent. In JPA, @ManyToOne and @OneToOne default to EAGER, while @OneToMany and @ManyToMany default to LAZY. Best practice is to make all associations lazy and fetch what each use case needs with JOIN FETCH or entity graphs, which avoids loading huge object graphs.
11

Using streams, find the employee with the highest salary in each department.

Java 8+ Features and StreamsMedium
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Group by department with a maxBy downstream collector. Map<String, Optional<Employee>> top = employees.stream() .collect(Collectors.groupingBy( Employee::department, Collectors.maxBy(Comparator.comparingInt(Employee::salary)))); To get values without Optional, wrap with collectingAndThen(maxBy(...), Optional::get), which is safe because each group has at least one element.
12

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

JDBC, Hibernate and JPAMedium
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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.
13

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

OOP in JavaMedium
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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.
14

Write a JDBC batch insert for a list of products.

JDBC, Hibernate and JPAMedium
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Batching sends many rows in one round trip. String sql = "INSERT INTO product(name, price) VALUES (?, ?)"; try (Connection c = ds.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) { c.setAutoCommit(false); int n = 0; for (Product p : products) { ps.setString(1, p.name()); ps.setLong(2, p.price()); ps.addBatch(); if (++n % 500 == 0) ps.executeBatch(); } ps.executeBatch(); c.commit(); }
15

How do you handle feedback that your code is too clever?

Java 8+ Features and StreamsEasy
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Situation: a reviewer said my one-line stream with nested collectors was hard to follow. Task: balance brevity with clarity. Action: I accepted the point, split the pipeline into named steps with small helper methods and added a comment on the business rule. Result: the next person who changed it did so without asking me, and I now aim for code a new joiner can read in one go.
16

Write a record with validation in its compact constructor.

OOP in JavaMedium
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A compact constructor runs before fields are assigned. public record Money(String currency, long paise) { public Money { Objects.requireNonNull(currency); if (paise < 0) { throw new IllegalArgumentException("negative amount"); } } public Money add(Money o) { return new Money(currency, paise + o.paise); } } Storing money in paise as long avoids floating point errors.
17

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

OOP in JavaMedium
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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.
18

Users get LazyInitializationException when the API returns an entity. What is happening?

JDBC, Hibernate and JPAMedium
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The entity was loaded inside a transaction, the session closed, and then Jackson touched a lazy association outside it. Do not fix it by turning on open-session-in-view or making everything eager. Instead, map the entity to a DTO inside the service transaction and fetch needed associations explicitly with JOIN FETCH or an entity graph. Spring Boot logs a warning because open-in-view is on by default.
19

Write a sealed interface with records and a switch that computes area.

Java 8+ Features and StreamsMedium
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The switch needs no default because the type set is closed. sealed interface Shape permits Circle, Rect {} record Circle(double r) implements Shape {} record Rect(double w, double h) implements Shape {} static double area(Shape s) { return switch (s) { case Circle c -> Math.PI * c.r() * c.r(); case Rect(double w, double h) -> w * h; }; }
20

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
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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.
21

How do you handle disagreement with a reviewer about your code?

Strings and Exception HandlingEasy
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Situation: a senior reviewer asked me to replace my checked exceptions with unchecked ones. Task: decide the right approach without conflict. Action: I asked for the reasons, read our codebase conventions and wrote a small comparison, then agreed because unchecked exceptions fit our global handler. Result: the change merged the same day and I learned to check team conventions before designing error handling.
22

What is a deadlock and how can it be prevented?

Multithreading and ConcurrencyMedium
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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.
23

You need to remove items from an ArrayList while looping over it. How do you do it safely?

Collections FrameworkEasy
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Removing inside a for-each loop throws ConcurrentModificationException. Use list.removeIf(item -> item.isExpired()), which is clear and efficient. Alternatives are an explicit Iterator calling iterator.remove(), or looping backwards by index. For large lists removeIf is best because it shifts elements once instead of on every removal.
24

Your service throws OutOfMemoryError: Java heap space in production. How do you investigate?

Java Basics and JVMHard
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First capture evidence: enable -XX:+HeapDumpOnOutOfMemoryError and check GC logs to see if heap grows steadily, which signals a leak, or spikes, which signals a large request. Analyse the heap dump in Eclipse MAT or VisualVM and look at the dominator tree for big retainers like static maps or caches. Fix the leak or bound the cache, then increase -Xmx only if the real workload needs it.
25

What is the difference between ArrayList and LinkedList?

Collections FrameworkEasy
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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.
26

A downstream payment service is slow and your API threads pile up. How do you protect your service?

Spring Boot and MicroservicesHard
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Set strict connect and read timeouts on the HTTP client. Add a Resilience4j circuit breaker so calls fail fast once the error rate crosses a threshold, a bulkhead to limit concurrent calls and retry with backoff only for safe idempotent requests. Return a clear fallback such as payment pending. Monitor breaker state through Actuator metrics and alerts.
27

Explain the main memory areas of the JVM.

Java Basics and JVMMedium
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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.
28

You need a cache that evicts the least recently used item when full. How would you build it in Java?

Collections FrameworkMedium
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Extend LinkedHashMap with accessOrder set to true and override removeEldestEntry to return true when size exceeds capacity. Each get moves the entry to the end, so the eldest is the least recently used. It is not thread safe, so wrap it with synchronization for shared use. In production prefer Caffeine, which offers size and time based eviction with high concurrency.
29

Why is the main method public static void?

Java Basics and JVMEasy
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It is public so the JVM can call it from outside the class, static so it can run without creating an object, and void because it returns nothing to the JVM; exit codes are set with System.exit(). The String[] args parameter receives command line arguments. From Java 21 onward, preview features allow simpler instance main methods for learning.
30

Write a thread safe singleton class in Java.

OOP in JavaMedium
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The simplest safe options are an enum or the holder idiom. public class Config { private Config() {} private static class Holder { static final Config INSTANCE = new Config(); } public static Config getInstance() { return Holder.INSTANCE; } } The JVM loads Holder lazily and class initialisation is thread safe. An enum singleton also resists reflection and serialization attacks.
31

How do you keep up with new Java releases?

Multithreading and ConcurrencyEasy
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Situation: our team was still on Java 8 while LTS releases moved ahead. Task: make a case for upgrading. Action: I followed release notes and JEPs, tried records, pattern matching and virtual threads in a side project, and built a proof of concept moving one service to Java 21 with measured gains. Result: the team approved the upgrade and I ran an internal session on the new features.
32

An API listing 100 orders fires 101 SQL queries. How do you fix it?

JDBC, Hibernate and JPAMedium
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This is the N+1 problem from a lazy association loaded in a loop or by JSON serialisation. Fetch what the endpoint needs in one query with JOIN FETCH or @EntityGraph(attributePaths = "items"), or use a DTO projection query. For collections with pagination, fetch ids first, then fetch associations in a second query to avoid in-memory paging. Add a test that asserts the query count.
33

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
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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.
34

Why must you be careful when initial capacity of a HashMap is too small?

Collections FrameworkHard
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If a HashMap starts small and grows large, it resizes many times; each resize allocates a new array and rehashes every entry, which costs CPU and creates garbage. When the expected size is known, use HashMap.newHashMap(n) in Java 19 or later, or set capacity to n divided by 0.75. Too large a capacity wastes memory, so size it to real data.
35

Bind typed configuration properties with validation in Spring Boot.

Spring Boot and MicroservicesMedium
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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.
36

Describe a time you had to learn a new technology quickly.

Java 8+ Features and StreamsMedium
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Situation: I joined a project using reactive Spring WebFlux with no prior experience. Task: contribute within two weeks. Action: I studied Project Reactor basics, built a small practice service, paired with a senior on my first ticket and kept notes on common operators. Result: I delivered my first feature in the second week and later wrote the team guide on avoiding blocking calls in reactive code.

Frequently asked questions

Which companies hire Java professionals in Ahmedabad?

Companies with large offices in Ahmedabad include many IT services and product firms. Use their company pages below to practise employer-specific sets.

Are Java interviews in Ahmedabad different from other cities?

The questions depend more on the company than the city. Ahmedabad's mix of employers decides the style: Companies here value hands-on skills and the ability to work across tools, especially in smaller teams

How do I find Java jobs in Ahmedabad?

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

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