36 practice questions with answers for Java interviews in Bhubaneswar.
Java jobs in Bhubaneswar
Bhubaneswar is eastern India's emerging IT hub, with campuses of large IT-services companies in Infocity and Info Valley. Freshers make up a big share of hiring, so fundamentals and aptitude rounds matter most.
Below are 36 questions that match the mix of service, product and domain employers hiring java developers in Bhubaneswar.
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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.
02
Count the frequency of each character in a string using Java.
A map with merge() is simple; streams also work.
Map<Character, Integer> freq = new LinkedHashMap<>();
for (char c : s.toCharArray()) {
freq.merge(c, 1, Integer::sum);
}
// Streams version
Map<Character, Long> f = s.chars()
.mapToObj(c -> (char) c)
.collect(Collectors.groupingBy(c -> c,
LinkedHashMap::new, Collectors.counting()));
LinkedHashMap keeps first-seen order.
03
An API needs to find the price band for any amount, for example the nearest lower slab. Which structure fits?
TreeMap is ideal because it keeps keys sorted and offers navigation methods. Store slab start amounts as keys and the band as value, then floorEntry(amount) returns the largest slab not above the amount in O(log n). ceilingKey, headMap and tailMap help with similar range queries such as tax slabs or delivery charges.
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.
05
toMap() throws Duplicate key exception in production. How do you fix it?
The data has repeated keys that the developer assumed were unique. Decide the business rule, then pass a merge function, for example toMap(User::email, u -> u, (a, b) -> a) to keep the first, or use groupingBy if all values are needed. Also check upstream data quality, since duplicates may signal a deeper bug such as missing unique constraints.
06
Read a large text file line by line efficiently and count lines containing ERROR.
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.
07
What is garbage collection and how does the JVM decide an object is garbage?
Garbage collection automatically frees memory used by objects that are no longer reachable. The JVM starts from GC roots such as local variables on thread stacks, static fields and active threads, and marks every object reachable from them. Anything not marked is garbage. Because reachability is used rather than reference counting, circular references between unreachable objects are still collected.
08
Describe a situation where you had to deliver under a tight deadline.
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.
09
Write a Spring Data JPA repository method that fetches orders with items to avoid N+1.
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.
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).
11
An API listing 100 orders fires 101 SQL queries. How do you fix it?
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.
12
Write a Java program to check whether a number is prime.
Check divisibility only up to the square root, which makes it O(sqrt n).
public static boolean isPrime(int n) {
if (n < 2) return false;
if (n % 2 == 0) return n == 2;
for (int i = 3; (long) i * i <= n; i += 2) {
if (n % i == 0) return false;
}
return true;
}
The long cast avoids overflow for large n.
13
A stream pipeline that updates a shared ArrayList in forEach gives random results with parallel(). Why?
ArrayList is not thread safe, and parallel streams run forEach on many threads, so additions race, get lost or throw exceptions. Side effects in streams are the problem. Replace forEach with collect(Collectors.toList()) or toList(), which handles merging per thread safely. Keep lambdas stateless and avoid modifying external state inside stream operations.
14
What is a ClassLoader and what is the delegation model?
A ClassLoader loads .class files into the JVM. The main loaders are Bootstrap (core classes), Platform (formerly Extension) and Application (classpath). In the parent delegation model a loader first asks its parent to load a class and only loads it itself if the parent cannot. This prevents user code from replacing core classes like java.lang.String.
15
What is the first level and second level cache in Hibernate?
The first level cache is the persistence context itself; it is per session or EntityManager, always on, and returns the same object for repeated finds by id in one transaction. The second level cache is shared across sessions and optional, backed by providers like Ehcache or Infinispan through JCache. Use it for read-mostly reference data, and be careful about stale data in clustered setups.
16
What is the difference between final, finally and finalize?
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 that runs after try-catch whether or not an exception occurs, used for cleanup. finalize() was a method called before garbage collection; it is deprecated for removal and should be replaced with try-with-resources or Cleaner.
17
Write a minimal Dockerfile for a Spring Boot application.
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.
18
What is the difference between an abstract class and an interface in modern Java?
An abstract class can have state (instance fields), constructors and any access modifier, and a class can extend only one. An interface has no instance state but, since Java 8, can have default and static methods, and since Java 9 private methods; a class can implement many. Use an interface for a capability contract and an abstract class to share code and state among closely related classes.
19
A counter shared between threads shows wrong totals. How do you fix it?
count++ is not atomic; two threads can read the same value and both write the same result, so updates are lost. Use AtomicInteger.incrementAndGet(), which uses CAS, or LongAdder for very high contention, as it spreads updates over cells. A synchronized method also works but is slower. volatile alone does not fix it because it gives visibility, not atomicity.
20
Tell me about a time a production incident happened because of your code.
Situation: a release I made caused failed payments for some users. Task: restore service and find the cause fast. Action: I rolled back within ten minutes, then found I had not handled a null bank code from one partner, which threw an exception. I fixed it, added validation and a test with that partner's data and shared a short write-up. Result: no repeat and the team added null checks to our review checklist.
21
What is Spring Boot and how is it different from the Spring Framework?
Spring Framework provides dependency injection, MVC, transactions and data access but needs manual configuration. Spring Boot builds on it with auto-configuration, starter dependencies, an embedded server such as Tomcat and production features through Actuator, so you can run a service with java -jar. Spring Boot 3 requires Java 17 or later and uses Jakarta EE packages instead of javax.
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.
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.
24
Write a JPQL query that returns a DTO projection instead of entities.
Projections load only needed columns and avoid dirty checking.
public record OrderSummary(Long id, String customer, long total) {}
@Query("""
select new com.shop.OrderSummary(o.id, c.name, o.total)
from Order o join o.customer c
where o.createdAt >= :from
""")
List<OrderSummary> summaries(@Param("from") LocalDate from);
Interface-based projections in Spring Data are another option.
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.
26
A getter returns an internal List and callers modify it, causing bugs. How do you fix this?
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.
Text blocks, final in Java 15, are multi-line string literals written between triple double quotes. They keep line breaks, remove common leading indentation and need far fewer escape characters, which makes embedded JSON, SQL and HTML readable. Methods like formatted() can insert values. They are still normal String objects in the pool.
28
Group a list of orders by city and sum the amount per city.
Use groupingBy with a summing collector.
Map<String, Double> totals = orders.stream()
.collect(Collectors.groupingBy(
Order::city,
TreeMap::new,
Collectors.summingDouble(Order::amount)));
TreeMap keeps cities sorted. For money, store amounts as long paise or BigDecimal and use Collectors.reducing with BigDecimal::add.
29
Print numbers 1 to 10 alternately from two threads (odd and even).
Use a shared lock with wait and notify.
class Printer {
int n = 1;
synchronized void print(boolean odd) throws InterruptedException {
while (n <= 10) {
if ((n % 2 == 1) == odd) {
System.out.println(Thread.currentThread().getName() + " " + n++);
notifyAll();
} else wait();
}
notifyAll();
}
}
Start one thread with print(true) and another with print(false).
30
What is the difference between method overloading and method overriding?
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.
Exception chaining wraps a low level exception in a higher level one while keeping the original as the cause, for example throw new OrderException("save failed", sqlEx). The full stack trace shows both, with Caused by lines. It lets each layer speak its own language without losing the root cause, which is essential when debugging production logs.
32
Is it good practice to catch Exception or Throwable?
Usually no. Catching Throwable also catches Errors like OutOfMemoryError that the app cannot recover from, and catching Exception hides bugs by treating all failures the same. Catch the most specific exceptions you can handle. A broad catch is acceptable only at a top boundary, such as a global handler or thread entry point, where you log and return a safe error.
33
A downstream payment service is slow and your API threads pile up. How do you protect your service?
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.
34
A query is fast in development but takes 8 seconds in production. How do you investigate?
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.
35
Exceptions are being swallowed with empty catch blocks in your codebase. How would you fix this?
Empty catches hide failures and make production issues invisible. I would find them with static analysis like SonarQube, then decide per case: handle the error properly, rethrow wrapped with context, or at least log with the stack trace. I would add a global exception handler for APIs and a team rule in code review and lint config to block new empty catch blocks.
36
Why must you be careful when initial capacity of a HashMap is too small?
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.
Few big employers listed in Bhubaneswar?
Many Bhubaneswar candidates also apply to teams in Kolkata and to remote or hybrid roles. Practise the Kolkata set as well.
Which companies hire Java professionals in Bhubaneswar?
Companies with large offices in Bhubaneswar include many IT services and product firms. Use their company pages below to practise employer-specific sets.
Are Java interviews in Bhubaneswar different from other cities?
The questions depend more on the company than the city. Bhubaneswar's mix of employers decides the style: Freshers make up a big share of hiring, so fundamentals and aptitude rounds matter most
How do I find Java jobs in Bhubaneswar?
Shortlist companies with Bhubaneswar offices, keep your CV focused on Java projects, apply on company career pages and job portals with the Bhubaneswar filter, and practise the questions on this page before each interview.