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Java Interview Questions in Pune

36 practice questions with answers for Java interviews in Pune.

Java jobs in Pune

Pune combines IT-services campuses in Hinjewadi and Kharadi with product, automotive and BFSI technology centres. It has a large mid-level job market for data and QA roles, and interviews are often practical and project-based.

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

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01

Explain the SOLID principles briefly.

OOP in JavaMedium
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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 records in Java and when should you use them?

OOP in JavaMedium
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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.
03

Write Java code to reverse an integer without converting it to a string.

Java Basics and JVMEasy
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Take the last digit with % 10 and build the result, checking for overflow. public static int reverse(int x) { long rev = 0; while (x != 0) { rev = rev * 10 + x % 10; x /= 10; } if (rev > Integer.MAX_VALUE || rev < Integer.MIN_VALUE) return 0; return (int) rev; } Negative numbers work because % keeps the sign in Java.
04

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.
05

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.
06

Explain pattern matching for switch and record patterns in Java 21.

Java 8+ Features and StreamsHard
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Pattern matching for switch lets a case match on type and bind a variable, such as case Circle c -> Math.PI * c.r() * c.r(). Record patterns deconstruct a record directly: case Point(int x, int y). Guards add conditions with when. With sealed types the compiler checks the switch is exhaustive, so adding a new subtype causes a compile error where it is not handled.
07

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.
08

Explain bean scopes in Spring.

Spring Boot and MicroservicesMedium
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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.
09

Memory usage is high because millions of Integer objects are stored in an ArrayList. What would you do?

Collections FrameworkHard
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Each Integer is a separate object with header overhead and a reference, so a List of Integer uses several times more memory than the raw data. If size is known, use an int[] array. Otherwise use primitive collections from libraries such as Eclipse Collections or fastutil, which store ints directly. This also improves cache performance and reduces GC pressure.
10

Describe a situation where you had to deliver under a tight deadline.

Multithreading and ConcurrencyMedium
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Situation: a bulk upload feature had to go live in four days for a client launch. Task: build it safely in time. Action: I split it into must-have and later items, used an ExecutorService to process rows in parallel, wrote focused tests for validation and kept the product owner updated daily. Result: we shipped on time, it handled 50,000 rows in under two minutes and we added the extras next sprint.
11

Write a Java method to check whether a string is a palindrome, ignoring case and non-letters.

Strings and Exception HandlingEasy
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Use two pointers from both ends. public static boolean isPalindrome(String s) { int i = 0, j = s.length() - 1; while (i < j) { char a = s.charAt(i), b = s.charAt(j); if (!Character.isLetterOrDigit(a)) { i++; continue; } if (!Character.isLetterOrDigit(b)) { j--; continue; } if (Character.toLowerCase(a) != Character.toLowerCase(b)) return false; i++; j--; } return true; } Time O(n), space O(1).
12

How do you take a thread dump and a heap dump of a running Java process?

Java Basics and JVMMedium
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Find the process id with jps or ps, then use jcmd, which is the recommended tool. jps -l jcmd <pid> Thread.print > threads.txt jcmd <pid> GC.heap_dump /tmp/heap.hprof Older tools jstack and jmap do the same. Take three thread dumps a few seconds apart to spot stuck threads, and analyse heap dumps in Eclipse MAT.
13

What is the difference between static and dynamic binding?

OOP in JavaMedium
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Static binding is resolved at compile time and applies to private, static and final methods and to overloaded methods, because the compiler knows exactly which method to call. Dynamic binding is resolved at runtime based on the actual object type and applies to overridden instance methods. Static methods are hidden, not overridden, so the reference type decides which one runs.
14

You have to process tasks in order of priority. Which collection do you use?

Collections FrameworkMedium
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Use PriorityQueue, a binary heap where poll() always returns the smallest element by natural order or by a Comparator, such as Comparator.comparingInt(Task::priority). Insert and poll are O(log n) and peek is O(1). For multiple threads use PriorityBlockingQueue. Iterating a PriorityQueue does not give sorted order; only repeated poll() does.
15

A log file shows a NullPointerException only for some users. How do you debug it?

Strings and Exception HandlingMedium
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Start with the stack trace; since Java 14 helpful NPE messages name exactly which variable was null. Reproduce with the failing user's data, which often has an optional field missing. Fix the root cause by validating input at the boundary, using Optional for values that may be absent and annotating with @NonNull. Add a unit test for that data case so it does not return.
16

What is the difference between Comparable and Comparator?

Collections FrameworkEasy
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Comparable defines a class's natural ordering through compareTo() inside the class, such as String sorted alphabetically. Comparator is a separate object with compare(), so you can define many orderings without changing the class. Java 8 made Comparator easy: Comparator.comparing(Employee::getSalary).reversed().thenComparing(Employee::getName). TreeMap and sort methods accept either.
17

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.
18

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.
19

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.
20

A file handle leak causes Too many open files errors after a day. What is the likely cause?

Strings and Exception HandlingHard
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Streams, readers or connections are opened but not closed on all paths, especially when an exception is thrown before close(). Check with lsof or jcmd which files are open. Fix by wrapping every resource in try-with-resources so it always closes, and make sure Files.lines() and Files.list() streams are closed too, since they hold file handles.
21

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

Spring Boot and MicroservicesMedium
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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.
22

What are sealed classes and how do they help?

OOP in JavaHard
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Sealed classes and interfaces, final in Java 17, restrict which classes can extend them using the permits clause, for example sealed interface Shape permits Circle, Square. Each subclass must be final, sealed or non-sealed. This models a closed set of types, and with pattern matching for switch in Java 21 the compiler can check that every case is handled without a default branch.
23

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.
24

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.
25

Implement an LRU cache using LinkedHashMap.

Collections FrameworkMedium
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Access order plus removeEldestEntry gives LRU in a few lines. class LruCache<K, V> extends LinkedHashMap<K, V> { private final int capacity; LruCache(int capacity) { super(16, 0.75f, true); this.capacity = capacity; } @Override protected boolean removeEldestEntry(Map.Entry<K, V> e) { return size() > capacity; } } get and put are O(1).
26

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

OOP in JavaEasy
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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.
27

Tell me about a time you found and fixed a difficult production bug in a Java application.

Java Basics and JVMMedium
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Situation: our order service crashed with OutOfMemoryError every few days. Task: find the root cause without long downtime. Action: I enabled heap dumps on OOM, analysed the dump in Eclipse MAT and found a static HashMap used as a cache that was never cleared. I replaced it with a bounded Caffeine cache with expiry and added a heap usage alert. Result: no crashes in six months and memory stayed flat.
28

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

JDBC, Hibernate and JPAMedium
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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 String constant pool?

Strings and Exception HandlingEasy
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The string pool is a special area in the heap where string literals are stored once and reused. String a = "hi" and String b = "hi" point to the same object. new String("hi") creates a separate heap object, and intern() returns the pooled copy. Pooling saves memory because many strings in apps repeat, such as status codes and keys.
30

What is optimistic versus pessimistic locking in JPA?

JDBC, Hibernate and JPAHard
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Optimistic locking adds a @Version column; on update Hibernate checks the version and throws OptimisticLockException if another transaction changed the row, so you retry. It suits low contention. Pessimistic locking uses SELECT FOR UPDATE through LockModeType.PESSIMISTIC_WRITE, blocking others until commit; it suits high contention on the same rows, like seat booking, but can reduce throughput.
31

Write a JDBC method to fetch a user by email safely.

JDBC, Hibernate and JPAEasy
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Use a PreparedStatement and try-with-resources. public Optional<User> findByEmail(String email) throws SQLException { String sql = "SELECT id, name FROM users WHERE email = ?"; try (Connection c = dataSource.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) { ps.setString(1, email); try (ResultSet rs = ps.executeQuery()) { if (rs.next()) return Optional.of(new User(rs.getLong(1), rs.getString(2))); } } return Optional.empty(); }
32

GC pauses of two seconds are causing request timeouts. How would you reduce them?

Java Basics and JVMHard
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Turn on GC logging with -Xlog:gc* and confirm which collections cause the pauses. Reduce allocation rate by fixing heavy object creation in hot paths. Size the heap correctly and set -Xms equal to -Xmx to avoid resizing. Tune G1 with MaxGCPauseMillis or move to ZGC for sub-millisecond pauses on large heaps. Retest under load before rolling out.
33

What is a functional interface?

Java 8+ Features and StreamsEasy
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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.
34

What is autoboxing and what pitfall can it cause?

Java Basics and JVMMedium
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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.
35

Why should we hire you as a Java backend developer?

Spring Boot and MicroservicesEasy
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Situation: in my current role I build Spring Boot services for a payments product. Task: show impact beyond writing code. Action: I improved API latency by 60 percent through query tuning and caching, raised test coverage from 40 to 80 percent and handled on-call calmly. Result: I bring solid Java, Spring and SQL skills, ownership of production and a habit of measuring results, which fits this role.
36

Sort a list of employees by department, then by salary descending.

Collections FrameworkEasy
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Chain comparators. employees.sort( Comparator.comparing(Employee::department) .thenComparing(Employee::salary, Comparator.reverseOrder())); // Streams version returning a new list List<Employee> sorted = employees.stream() .sorted(Comparator.comparing(Employee::department) .thenComparing(Employee::salary, Comparator.reverseOrder())) .toList(); List.sort is stable, so equal keys keep their order.

Companies with offices in Pune (13)

IT services

TCS

Java interview questions

  • 30 questions
  • 4 rounds

Mumbai, Chennai, Pune +2

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IT services

Infosys

Java interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Mysuru, Pune +2

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IT services

Wipro

Java interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Hyderabad, Pune +2

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Consulting

Accenture

Java interview questions

  • 30 questions
  • 4 rounds

Bengaluru, Hyderabad, Pune +2

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IT services

Cognizant

Java interview questions

  • 30 questions
  • 4 rounds

Chennai, Bengaluru, Pune +2

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IT services

Capgemini

Java interview questions

  • 30 questions
  • 4 rounds

Mumbai, Bengaluru, Pune +2

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IT services

Tech Mahindra

Java interview questions

  • 30 questions
  • 4 rounds

Pune, Hyderabad, Bengaluru +2

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IT services

LTIMindtree

Java interview questions

  • 30 questions
  • 4 rounds

Mumbai, Pune, Bengaluru +2

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Product

Amazon

Java interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Hyderabad, Chennai +2

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Product

Oracle

Java interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Hyderabad, Noida +2

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Banking & finance

Barclays

Java interview questions

  • 30 questions
  • 4 rounds

Pune, Chennai, Noida +1

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Fintech

PhonePe

Java interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Pune

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Product

SAP

Java interview questions

  • 30 questions
  • 5 rounds

Bengaluru, Gurugram, Pune +1

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Frequently asked questions

Which companies hire Java professionals in Pune?

Companies with large offices in Pune include TCS, Infosys, Wipro, Accenture, Cognizant, Capgemini, Tech Mahindra, LTIMindtree, Amazon, Oracle. Use their company pages below to practise employer-specific sets.

Are Java interviews in Pune different from other cities?

The questions depend more on the company than the city. Pune's mix of employers decides the style: It has a large mid-level job market for data and QA roles, and interviews are often practical and project-based

How do I find Java jobs in Pune?

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

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