Object-Oriented Programming
1. How would you design a class hierarchy for a media player application supporting multiple media formats (audio, video)?Discuss the use of abstract classes and interfaces to handle different media types.
2. Design a parking lot system where different types of vehicles occupy different amounts of space. How would you model this in Java? Explain how you would use inheritance, polymorphism, and possibly enums to differentiate vehicle types.
3. How would you implement a singleton class that is safe for multithreading? Discuss different approaches like using synchronized, volatile, or Bill Pugh Singleton design.
4. Explain how you would implement a cache that is both thread-safe and can expire entries after a certain time. Discuss the use of ConcurrentHashMap and ScheduledExecutorService or WeakReference.
5. Design a system where users can create and manage to-do lists. What classes would you create, and how would they interact? Discuss class design, encapsulation, and how to manage the interactions between tasks and lists.
Collections and Data Structures
6. How would you implement a custom data structure that behaves like a queue but also allows random access? Discuss a hybrid structure using a List and Deque or LinkedList.
7. Design a system to manage a leaderboard for a game, where scores are updated frequently. Discuss how you would maintain the leaderboard using TreeMap or PriorityQueue.
8. Given a list of transactions, how would you remove duplicates efficiently? Discuss the use of Set or custom methods like overriding equals() and hashCode().
9. How would you implement a system that handles a large number of user logs and needs to retrieve the most recent entries quickly? Discuss using LinkedList or a Deque structure for efficient recent log retrieval.
10. Describe how you would implement a real-time messaging system with a priority queue. Discuss the use of PriorityQueue and how messages can be prioritized and processed.
Exception Handling
11. How would you design a custom exception hierarchy for an online shopping application? Discuss how to create base exceptions and specific exceptions for different error conditions.
12. You have a method that interacts with a database and may throw multiple types of exceptions. How would you handle this? Discuss handling exceptions in a way that doesn't expose internal details to the user.
13. In a banking application, you need to ensure that transactions are rolled back if any error occurs. How would you implement this? Discuss using try-catch-finally blocks and possibly transaction management APIs.
14. How would you handle exceptions in a multi-threaded environment where you need to log errors from each thread? Discuss using Thread.UncaughtExceptionHandler or centralized logging.
15. Explain how you would design an API where clients need to handle specific exceptions differently. Discuss designing methods with well-defined checked exceptions and custom error codes.
Multithreading and Concurrency
16. How would you implement a thread-safe producer-consumer model in Java? Discuss using BlockingQueue, wait(), notify(), or other concurrency utilities.
17. Design a system where multiple threads can read a shared resource, but only one thread can write to it at a time. Discuss using ReadWriteLock or ReentrantReadWriteLock.
18. How would you implement a feature where multiple threads are processing data, and you need to aggregate their results? Discuss using ExecutorService, Future, and CompletionService.
19. Explain how you would implement a rate limiter for an API using multithreading in Java. Discuss token bucket algorithms and using Semaphore or ScheduledExecutorService.
20. Design a system where you have to run a batch of tasks with dependencies between them. How would you ensure proper execution order? Discuss using ForkJoinPool, CountDownLatch, or CompletableFuture.
I/O and Serialization
21. How would you implement a file reading system that needs to process large files without loading the entire file into memory? Discuss using streams, BufferedReader, or memory-mapped files.
22. Design a logging system that writes logs to a file, ensuring minimal impact on application performance. Discuss using asynchronous logging with a BlockingQueue or frameworks like Log4j.
23. Explain how you would design a system where different parts of an application need to serialize and deserialize objects differently. Discuss custom serialization with Externalizable or JSON/XML libraries.
24. How would you implement a service that continuously monitors a directory for new files and processes them as they arrive? Discuss using WatchService API for file system events.
25. Design a system to handle streaming data (e.g., video, audio) efficiently in Java. Discuss using NIO, non-blocking I/O, and channels.
Memory Management
26. How would you design a memory-sensitive cache that can automatically remove the least recently used items when memory is low? Discuss using LinkedHashMap for LRU cache or libraries like Guava.
27. What steps would you take to optimize the memory usage of a Java application that handles large datasets? Discuss techniques like object pooling, lazy loading, and optimizing data structures.
28. How would you identify and fix a memory leak in a Java application? Discuss using tools like VisualVM, heap dumps, and analyzing references.
29. Explain how you would design a system that minimizes garbage collection overhead in a high-throughput application. Discuss object reuse, minimizing temporary objects, and tuning GC parameters.
30. How would you implement a system where certain objects need to be available in memory as long as they are being referenced, but can be cleaned up otherwise? Discuss using WeakReference, SoftReference, or PhantomReference.
Reflection and Annotations
31. How would you implement a generic logging mechanism that logs method execution details using annotations? Discuss using custom annotations, reflection, and AOP.
32. Explain how you would use reflection to dynamically load classes and invoke methods in a plugin system. Discuss class loading, Method and Field objects, and ClassLoader.
33. How would you design a system that validates objects against custom rules defined using annotations? Discuss using annotations, reflection, and possibly creating a validation framework.
34. Design a system where certain methods should be executed based on the presence of specific annotations at runtime. Discuss scanning annotations with reflection and method invocation.
35. How would you implement a dependency injection framework using reflection in Java? Discuss identifying dependencies via annotations, creating instances, and injecting them.
Functional Programming
36. How would you implement a system where you need to filter, transform, and aggregate data from a collection? Discuss using Java Streams and functional interfaces like Predicate, Function, and Collector.
37. Design a system where you need to apply a series of transformations to a collection of data in a pipeline fashion. Discuss chaining operations with Streams and method references.
38. Explain how you would implement a system that can parallelize certain operations on a collection of data. Discuss using parallel streams and their trade-offs.
39. How would you design a custom functional interface to represent a complex operation that can be composed with other operations? Discuss functional interfaces, lambdas, and default methods for composition.
40. Explain how you would use the Optional class to avoid NullPointerException in a legacy codebase. Discuss refactoring methods to return Optional and using its API for null safety.
Java 8+ Features
41. How would you refactor a legacy codebase to use Java 8 Streams for improved readability and performance?Discuss identifying areas where Streams can replace loops and collections operations.
42. Explain how you would design an application that makes use of CompletableFuture for asynchronous programming. Discuss chaining futures, handling exceptions, and combining multiple asynchronous tasks.
43. Design a system where you need to group and summarize data from a collection of objects using Java 8 Streams. Discuss using Collectors like groupingBy, partitioningBy, and reducing.
44. How would you use Java 8’s Optional and Stream APIs to handle potentially empty collections gracefully? Discuss handling empty streams, filtering, and using Optional to prevent null checks.
45. Explain how you would implement a multi-threaded application that processes data using Java 8’s parallel streams. Discuss parallel streams, fork-join pool, and performance considerations.
Advanced Java
JDBC and Database Interaction
46. How would you design a system that interacts with a database but needs to ensure database vendor independence? Discuss using JDBC with a DAO pattern or ORM like Hibernate.
47. Explain how you would manage transactions in a system where multiple database operations need to be executed atomically. Discuss using JDBC transaction management or Spring's transaction support.
48. How would you implement a batch processing system that reads from and writes to a database efficiently? Discuss using JDBC batch updates and managing transactions.
49. Design a system where you need to handle complex SQL queries and map the results to Java objects. Discuss using ResultSet, RowMapper, or an ORM tool.
50. Explain how you would implement a connection pooling mechanism in a high-traffic web application. Discuss using connection pool libraries like HikariCP or Apache DBCP.
Servlets and Web Applications
51. How would you design a servlet-based web application that handles file uploads and downloads securely? Discuss handling multipart requests, securing file paths, and proper I/O handling.
52. Explain how you would implement session management in a web application that needs to scale horizontally. Discuss using session replication, sticky sessions, or external session storage.
53. Design a RESTful API in Java using servlets, ensuring that it follows industry best practices. Discuss HTTP methods, proper status codes, and exception handling.
54. How would you secure a servlet-based application against common web vulnerabilities like XSS and CSRF? Discuss input validation, escaping output, and implementing CSRF tokens.
55. Explain how you would implement request filtering and interception in a servlet-based application. Discuss using servlet filters and interceptors for cross-cutting concerns.
Spring Framework
56. How would you design a Spring Boot application that handles configuration changes dynamically at runtime? Discuss using Spring Cloud Config or @RefreshScope.
57. Explain how you would implement a microservice in Spring Boot that communicates with other services asynchronously. Discuss using @Async, messaging queues, or RESTful APIs with CompletableFuture.
58. How would you design a RESTful API with Spring Boot that supports versioning and handles deprecated versions gracefully? Discuss URL versioning, content negotiation, and deprecation strategies.
59. Design a Spring application that uses dependency injection to manage complex object graphs. Discuss using @Autowired, @Qualifier, and Java-based configuration.
60. Explain how you would implement a role-based access control system in a Spring Security application. Discuss using @PreAuthorize, @Secured, and custom permission evaluators.
Hibernate and JPA
61. How would you design a system using Hibernate that needs to handle large datasets with minimal memory usage? Discuss lazy loading, pagination, and caching strategies.
62. Explain how you would implement a multi-tenancy application using Hibernate. Discuss approaches like database schema per tenant, shared schema, or discriminator column.
63. Design a system where you need to handle complex entity relationships (one-to-many, many-to-many) using JPA. Discuss mapping strategies, join tables, and cascade operations.
64. How would you implement a search functionality in a Hibernate-based application that needs to support complex filtering? Discuss using Criteria API, HQL, or JPQL.
65. Explain how you would manage transactions and concurrency in a Hibernate-based application. Discuss transaction isolation levels, optimistic locking, and versioning.
Web Services and APIs
66. How would you design a RESTful web service that needs to handle high traffic and large payloads? Discuss REST API best practices, pagination, and streaming large payloads.
67. Explain how you would secure a RESTful web service in Java. Discuss using OAuth2, JWT, and HTTPS.
68. Design a SOAP web service in Java that supports complex types and custom headers. Discuss using JAX-WS, WSDL, and JAXB for object mapping.
69. How would you implement a rate limiting feature for a REST API to prevent abuse? Discuss strategies like API Gateway, throttling, and using Redis for tracking requests.
70. Explain how you would design an API gateway that routes requests to multiple microservices. Discuss using Spring Cloud Gateway or Zuul, and managing cross-cutting concerns.
Microservices Architecture
71. How would you design a microservices architecture for an e-commerce application? Discuss service decomposition, database per service, and inter-service communication.
72. Explain how you would handle service discovery and load balancing in a microservices environment. Discuss using Eureka, Consul, or Kubernetes for service discovery and Ribbon or Zuul for load balancing.
73. How would you implement inter-service communication in a microservices architecture, considering both synchronous and asynchronous scenarios? Discuss using RESTful APIs, gRPC, message brokers like RabbitMQ or Kafka.
74. Design a circuit breaker mechanism for handling failures in a microservices architecture. Discuss using Hystrix, Resilience4j, or Spring Cloud Circuit Breaker.
75. Explain how you would implement a centralized logging solution for microservices. Discuss using ELK stack (Elasticsearch, Logstash, Kibana), or distributed tracing with Jaeger or Zipkin.
Performance Tuning and Scalability
76. How would you diagnose and fix a performance bottleneck in a Java web application? Discuss using profilers, analyzing thread dumps, and tuning JVM parameters.
77. Explain how you would design a system to handle spikes in traffic without degrading performance. Discuss auto-scaling, load balancing, and caching strategies.
78. How would you implement caching in a high-throughput application to reduce database load? Discuss using distributed caches like Redis, Ehcache, or Hazelcast.
79. Design a system where you need to process and store large amounts of data in real-time. Discuss using big data technologies, distributed processing, and data partitioning.
80. Explain how you would optimize a Java application for low latency. Discuss minimizing GC pauses, tuning JVM parameters, and using efficient data structures.
Testing and Continuous Integration
81. How would you design a testing strategy for a complex Java application with many dependencies? Discuss unit testing, integration testing, and mocking frameworks like Mockito.
82. Explain how you would set up continuous integration for a Java project with multiple modules. Discuss using tools like Jenkins, Maven, or Gradle and managing dependencies between modules.
83. How would you test a multithreaded application to ensure it is free of concurrency issues? Discuss using concurrency testing tools like ConTest or JUnit with custom rules for multithreading.
84. Design a system where you can automatically run performance tests as part of your CI/CD pipeline. Discuss integrating JMeter or Gatling with Jenkins and analyzing results.
85. Explain how you would implement automated testing for a REST API using Java. Discuss using REST Assured, Postman, or JUnit for API testing.
Security
86. How would you secure sensitive data in a Java application that needs to be stored in a database? Discuss using encryption libraries, secure storage, and ensuring secure key management.
87. Explain how you would design a secure authentication and authorization system for a Java web application. Discuss using Spring Security, OAuth2, and role-based access control.
88. How would you protect a Java application from SQL injection attacks? Discuss using prepared statements, ORM frameworks, and input validation.
89. Design a system where you need to securely transmit data between a client and server in Java. Discuss using HTTPS, SSL/TLS, and possibly encrypting payloads.
90. Explain how you would implement logging in a Java application to avoid exposing sensitive information. Discuss best practices for logging, redacting sensitive data, and using secure logging frameworks.
Emerging Technologies and Trends
91. How would you implement a reactive application in Java that needs to handle a large number of concurrent users? Discuss using Project Reactor, WebFlux, or Akka.
92. Explain how you would design a cloud-native Java application. Discuss using Spring Cloud, microservices, containerization with Docker, and orchestration with Kubernetes.
93. How would you implement a blockchain client in Java that interacts with a decentralized network? Discuss using libraries like Web3j for Ethereum or Hyperledger Fabric SDK.
94. Design a serverless function in Java that processes events from a message queue. Discuss using AWS Lambda, Google Cloud Functions, or Azure Functions with Java.
95. Explain how you would use Java to build and deploy a machine learning model. Discuss using libraries like DL4J, TensorFlow Java API, and deployment strategies.
Java Ecosystem Tools and Frameworks
96. How would you set up a Maven multi-module project for a complex Java application? Discuss parent POMs, module inheritance, and managing dependencies.
97. Explain how you would design a build pipeline using Jenkins for a Java project with multiple environments (dev, test, prod). Discuss using Jenkins pipelines, environment variables, and deployment strategies.
98. How would you use Gradle to manage dependencies and build a large Java application? Discuss using Gradle’s build script, dependency configurations, and custom tasks.
99. Design a system where you need to monitor the performance and health of a Java application in production. Discuss using monitoring tools like Prometheus, Grafana, or New Relic.
100. Explain how you would containerize a Java application and deploy it to a cloud environment. - Discuss using Docker, creating Dockerfiles, and deploying with Kubernetes or cloud services.
