IBM Interview Questions

#1Explain the SOLID principles.

#2How does HashMap work internally?

#3What is the difference between HashMap and ConcurrentHashMap?

#4Explain Java Memory Model: Heap, Stack, and Metaspace.

#5What is the volatile keyword in Java?

#6What is the difference between synchronized and ReentrantLock?

#7What is a deadlock and how do you prevent it?

#8Explain the Stream API and intermediate vs terminal operations.

#9What is garbage collection? How does G1 differ from ZGC?

#10What is the Java ClassLoader hierarchy?

#11What are Java records (Java 16+)?

#12What is the Executor framework and when would you use it over raw Threads?

#13What is the difference between composition and inheritance?

#14What is a marker interface? Give examples.

#15What are the design patterns most commonly asked in Java interviews?

#16How do you implement a Singleton in Java correctly?

#17What is the contract between equals() and hashCode()?

#18What is the difference between fail-fast and fail-safe iterators?

#19What is CopyOnWriteArrayList and when should you use it?

#20How does PriorityQueue work and when would you use it?

#21What is the happens-before relationship in Java Memory Model?

#22What is the difference between sleep(), wait(), and yield()?

#23What are atomic classes (AtomicInteger, AtomicReference)? How do they work?

#24What is a CountDownLatch vs CyclicBarrier?

#25What is a ThreadLocal and what are its dangers?

#26What is a CompletableFuture and how does it improve async programming?

#27What are virtual threads (Project Loom, Java 21)?

#28How does the JIT (Just-In-Time) compiler work?

#29What is the difference between minor GC, major GC, and full GC?

#30What tools do you use to diagnose JVM memory issues?

#31What is the String pool and how does string interning work?

#32What is type erasure in Java generics?

#33What is the difference between <? extends T> and <? super T>?

#34What are sealed classes (Java 17)?

#35What is pattern matching for instanceof (Java 16)?

#36What is the difference between map() and flatMap() in streams?

#37What is the difference between Comparable and Comparator?

#38What is Stream.collect() and what are common Collectors?

#39What is try-with-resources and how does it work?

#40What is exception chaining and why is it important?

#41What is the difference between Java IO and NIO?

#42What is Java Serialization and what are its pitfalls?

#43What is reflection in Java and when is it used?

#44What is the difference between deep copy and shallow copy?

#45What is autoboxing and unboxing? What are the performance implications?

#46What are enums in Java and what advanced features do they support?

#47What is the difference between static and instance initializer blocks?

#48What are Java modules (Java 9 — JPMS)?

#49What is the difference between an inner class, static nested class, and anonymous class?

#50What are the new switch expressions (Java 14)?

#51What is the difference between Runnable, Callable, and Future?

#52How do you handle NullPointerException in Java?

#53What is the difference between Deque and Queue?

#54What is a WeakHashMap and when would you use it?

#55What is the difference between checked and unchecked exceptions — best practices for APIs?

#56What is the difference between interface default methods and abstract class methods?

#57What are the best practices for writing clean Java code?

#58What is a race condition and how do you prevent it?

#59What is the difference between HashMap.computeIfAbsent() and getOrDefault()?

#60What is the purpose of the transient keyword?

#61What is method hiding in Java?

#62What are the Java 8 Date/Time APIs and why were they introduced?

#63What is the difference between HashMap.put() and HashMap.putIfAbsent()?

#64What is an immutable class and how do you create one?

#65What is the covariant return type in Java?

#66What is the difference between Predicate.and(), Predicate.or(), and Predicate.negate()?

#67What is the Observer pattern and how is it implemented in Java?

#68What is the Strategy pattern in Java?

#69What is String.intern() and when should you use it?

#70What are the key differences between Java 8, 11, 17, and 21?

#71Explain the CAP theorem.

#72What is consistent hashing and why is it used?

#73What is database sharding and how does it work?

#74Explain cache invalidation strategies.

#75How would you design a URL shortener (like bit.ly)?

#76What is the Saga pattern in microservices?

#77What is CQRS and when should you use it?

#78What are rate limiting algorithms?

#79What is the Circuit Breaker pattern?

#80How do you design for high availability?

#81What is eventual consistency?

#82What is a message queue and when should you use one?

#83What is the difference between SQL and NoSQL databases?

#84How do you handle distributed transactions without 2PC?

#85How would you design a notification system (push, email, SMS)?

#86What is the difference between REST and gRPC?

#87What is the Outbox Pattern?

#88How do you design a distributed cache layer?

#89What is the difference between synchronous and asynchronous communication in microservices?

#90How do you design a notification system that sends 100M notifications per day?

#91What are the different types of database indexes and when do you use each?

#92How would you design a URL shortener like bit.ly?

#93What is eventual consistency and how do you handle it in practice?

#94How do you design a search system at scale?

#95What is the difference between optimistic and pessimistic locking?

#96How would you design a real-time leaderboard?

#97What is a write-ahead log (WAL) and how is it used?

#98How do you handle distributed transactions across microservices?

#99How do you design a chat application like WhatsApp?

#100What is a service mesh and when should you use one?

#101How would you design a video streaming platform like YouTube?

#102What is the difference between a load balancer and an API gateway?

#103How do you prevent and handle cascading failures in distributed systems?

#104What is the difference between a message queue and a message broker?

#105How do you design a rate limiter for an API?

#106What is the difference between replication and partitioning in databases?

#107How would you design Twitter's news feed?

#108What is observability and what are its three pillars?

#109How do you implement idempotency in APIs?

#110How would you design a distributed job scheduler?

#111What is the Saga pattern vs 2PC for distributed transactions?

#112How do you design a file storage system like Dropbox?

#113What are the trade-offs of microservices vs monolithic architecture?

#114How does DNS work and how is it used in load balancing?

#115What is the strangler fig pattern?

#116How do you design an e-commerce inventory system that handles flash sales?

#117What is the difference between push and pull architectures for data?

#118How do you design a fraud detection system?

#119What is event sourcing and how does it differ from CRUD?

#120How would you design a geospatial service like Uber's nearby driver system?

#121What is API versioning and what are the different strategies?

#122What is a Bloom filter and where is it used in system design?

#123How do you implement zero-downtime deployments?

#124What is the two-generals problem and what does it tell us about distributed systems?

#125How do you design a payment processing system?

#126How would you design an autocomplete system?

#127What is backpressure and how do you handle it?

#128What is a time-series database and when should you use one?

#129What is a circuit breaker and how do you implement it?

#130How do you handle database migrations safely in production?

#131What is the CQRS pattern?

#132How do you secure an API at the architecture level?

#133What is the difference between synchronous replication and asynchronous replication?

#134How do you design a system for billions of events per day (analytics pipeline)?

#135What is chaos engineering and how do you implement it?

#136What is the database connection pool and how do you tune it?

#137How do you design an access control system?

#138How would you design an online code execution system like LeetCode?

#139How does the request flow work in a typical microservices architecture?

#140What is a hot partition problem and how do you solve it?

#141How do you design a multi-tenant SaaS architecture?

#142What is tail latency and why does it matter?

#143How do you design a global, low-latency key-value store?

#144What is the N+1 query problem and how do you fix it?

#145How would you design a booking system like Airbnb?

#146How do you design a recommendation system?

#147What is the read-your-own-writes consistency guarantee?

#148How do you design a search-as-you-type / typeahead feature?

#149What is the difference between gRPC unary, server streaming, client streaming, and bidirectional streaming?

#150How do you handle large file uploads efficiently?

#151What are the key considerations when designing for high write throughput?

#152What is the difference between monolithic and microservices deployment strategies?

#153How do you design for disaster recovery?

#154What is the thundering herd problem?

#155What is a vector clock and how does it work?

#156What is the difference between a monorepo and polyrepo?

#157How do you ensure data consistency across microservices?

#158What is the difference between a batch job and a stream processing job?

#159How do you design an API for mobile clients vs web clients?

#160What is the role of a message broker in event-driven architecture?

#161How do you approach capacity planning for a new system?

#162What is an API Gateway and what does it do?

#163How do microservices communicate?

#164What is service discovery in microservices?

#165What is the Circuit Breaker pattern and how does it prevent cascading failures?

#166What is distributed tracing and why is it important?

#167What is the Strangler Fig pattern for microservices migration?

#168What is a sidecar pattern?

#169How do you manage configuration in microservices?

#170What are the 12-Factor App principles?

#171What is event-driven architecture and when should you use it?

#172What is the difference between orchestration and choreography in Saga?

#173How do you test microservices effectively?

#174What is a service mesh and when should you use one?

#175How do you ensure data consistency across microservices?

#176What is the circuit breaker pattern?

#177What is service discovery and how does it work?

#178What is the Bulkhead pattern?

#179What is the Retry pattern and how do you implement it safely?

#180What is the difference between choreography and orchestration in Sagas?

#181What is the Backend for Frontend (BFF) pattern?

#182How do you implement distributed tracing?

#183What is the Strangler Fig pattern for migrating a monolith?

#184What is eventual consistency and how do you design for it?

#185How do you version microservice APIs?

#186What is the Sidecar pattern?

#187What is a dead letter queue and why is it important?

#188How do you implement health checks in microservices?

#189What is the Outbox pattern and how does it guarantee event delivery?

#190What is idempotency and how do you implement it in microservices?

#191What are the 12-Factor App principles?

#192How do you handle secrets management in microservices?

#193What is the Ambassador pattern in microservices?

#194How do you implement inter-service authentication?

#195What is the Throttling pattern and how does it differ from rate limiting?

#196What is CQRS and how does it apply to microservices?

#197How do you test microservices?

#198What is service isolation and why is it important?

#199What is an Event-Driven Architecture?

#200How do you handle database per service in practice?

#201What is the Role of API composition in microservices?

#202What is graceful degradation in microservices?

#203What is the Event Sourcing pattern?

#204How do you implement logging in a microservices environment?

#205What is the two-phase commit vs Saga for distributed transactions?

#206How do you handle timeouts in microservices?

#207What is the Scatter-Gather pattern?

#208What is the difference between a microservice and a nanoservice?

#209How do you implement canary deployments in microservices?

#210What is a Service Registry?

#211What is blue-green deployment and how does it work?

#212What is the Aggregator pattern?

#213How do microservices handle configuration management?

#214What is the Proxy pattern in microservices?

#215How do you implement distributed locking in microservices?

#216What is Kafka and why is it popular in microservices?

#217How do you manage service dependencies in microservices?

#218What is a bounded context?

#219How do you implement a request-reply pattern over async messaging?

#220What is the Token Bucket algorithm and how is it used for rate limiting?

#221How do you handle schema evolution in event-driven systems?

#222What is the difference between a monolith, microservices, and modular monolith?

#223What is the Choreography pattern in detail?

#224What is a composite microservice?

#225How do you deal with "chatty" microservices?

#226What is a process manager / workflow engine in microservices?

#227How do you implement zero-downtime deployments for microservices?

#228What is the Anti-Corruption Layer pattern?

#229What are the common pitfalls of microservices adoption?

#230What is the difference between orchestration and choreography?

#231How do you implement a consistent read across microservices?

#232What is load shedding?

#233What is the difference between gRPC and REST for inter-service communication?

#234What is the Gateway Aggregation pattern vs Gateway Routing?

#235What is the Inbox pattern?

#236How do you handle versioning of events in Kafka?

#237What is the Open Host Service pattern?

#238How do you implement service-level SLOs in microservices?

#239What is the Claim Check pattern?

#240What is service mesh traffic management?

#241What is the difference between horizontal and vertical scaling for microservices?

#242What is the role of a message schema registry?

#243How do you handle service discovery with Kubernetes?

#244How do you implement an API gateway from scratch?

#245What is consumer-driven contract testing (Pact)?

#246How do you use feature toggles in microservices?

#247What is polyglot persistence in microservices?

#248What are distributed caching strategies for microservices?

#249How do you design a CI/CD pipeline for microservices?

#250How do you implement observability with Micrometer, Prometheus, and Grafana?

#251What is the Retry pattern and when should you NOT retry?

#252How do you implement Saga compensation (rollback) in detail?

#253What is multi-tenancy in microservices and how do you implement it?

#254What are the steps to migrate a monolith to microservices using the Strangler Fig pattern?

#255How do you design microservices for failure?

#256What is data mesh and how does it relate to microservices data ownership?

#257What is a sidecar proxy and how does Envoy work?

#258How do you handle inter-service authorization (not just authentication)?

#259When should you NOT use microservices?

#260What is a consumer group and how does it enable parallelism?

#261Explain Kafka delivery semantics: at-most-once, at-least-once, and exactly-once.

#262How does Kafka ensure message ordering?

#263What are producer acknowledgment settings (acks)?

#264What is log compaction in Kafka?

#265What is Kafka Streams and when would you use it?

#266What is consumer lag and how do you monitor it?

#267How does Kafka differ from RabbitMQ?

#268What is the role of ZooKeeper / KRaft in Kafka?

#269How do you handle large messages in Kafka?

#270What is Kafka Connect?

#271How does Kafka replication work?

#272What is Schema Registry and why is it important?

#273What is the difference between Kafka and RabbitMQ?

#274How do you handle consumer group rebalancing?

#275What is Kafka Streams?

#276What are Kafka transactions and how do they work?

#277What is the difference between at-most-once, at-least-once, and exactly-once delivery?

#278How do you choose the right number of partitions for a Kafka topic?

#279What is KRaft mode in Kafka?

#280What is log compaction in Kafka?

#281How does Kafka handle backpressure?

#282What is the role of the Kafka controller?

#283What is the difference between Kafka producer acks=0, acks=1, and acks=all?

#284How do you monitor Kafka in production?

#285What is a Kafka consumer poll loop?

#286What are Kafka headers and how are they used?

#287What is the consumer group coordinator?

#288How do you implement idempotent consumers with Kafka?

#289What is Kafka's storage architecture?

#290What is consumer lag and how do you manage it?

#291What is the Kafka retention policy and how does it work?

#292How do you handle poison pill messages in Kafka?

#293What is Kafka MirrorMaker 2 and when do you use it?

#294How does Kafka achieve high throughput?

#295What is Kafka's ISR (In-Sync Replicas) and how does it affect durability?

#296What are Kafka Streams stateful operations?

#297What is the difference between Kafka Streams and Apache Flink?

#298How does Kafka handle message ordering?

#299What is Kafka's __consumer_offsets topic?

#300How do you implement a CDC pipeline with Kafka and Debezium?

#301What is the difference between push and pull in Kafka?

#302How do you perform a Kafka cluster rolling restart?

#303What is Kafka consumer group offset management?

#304What is Kafka's batch processing capability?

#305What is the relationship between Kafka partitions and consumers?

#306What is the Kafka producer buffer and how does it affect performance?

#307How does Kafka support exactly-once semantics end to end?

#308What is Kafka's message format / record format?

#309How does Kafka handle broker failure and partition recovery?

#310What is Kafka's wire protocol?

#311What are Kafka consumer interceptors?

#312How do you secure a Kafka cluster?

#313What is Kafka's log segment management?

#314How do you increase the throughput of a Kafka producer?

#315What is the Kafka AdminClient API?

#316What is tiered storage in Kafka?

#317How does Kafka handle time and event-time processing?

#318What is Kafka's producer idempotence?

#319What are the different Kafka message delivery patterns?

#320How do you tune Kafka for low latency?

#321What is Kafka's producer partitioner?

#322What is the Kafka Broker Rack Awareness?

#323How do you handle schema migrations in a Kafka event stream?

#324What are Kafka quotas and how do they work?

#325What is a Kafka topic compaction tombstone?

#326How do you implement a Kafka consumer with Spring Boot?

#327What is the Kafka offset commit semantics?

#328How do you benchmark a Kafka cluster?

#329What is the difference between Kafka and Apache Pulsar?

#330How do you implement a Kafka producer with Spring Boot?

#331What is a Kafka connector and how does it work?

#332What is the Kafka consumer fetch protocol?

#333What is Kafka consumer group rebalance protocol and incremental cooperative rebalancing?

#334What is the Kafka log cleaner and how does compaction work internally?

#335How do you debug Kafka consumer issues?

#336What is Kafka's min.insync.replicas and how does it interact with acks?

#337What is Apache Kafka's role in the data lakehouse architecture?

#338What is the Kafka log flush policy and how does it affect durability?

#339How do you implement a Saga with Kafka?

#340What is the difference between Kafka topic partitions and consumer group partitions?

#341What is Confluent's ksqlDB?

#342What is Kafka's message size limit and how do you handle large messages?

#343What are Kafka producer callbacks and how are they used?

#344How do you implement a Kafka multi-datacenter setup?

#345What is Kafka's leader epoch?

#346What is the high watermark in Kafka?