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System Design Objective Questions and Answers
This Java System Design quiz contains carefully curated objective questions with correct answers and clear explanations. It is designed for backend engineers, platform engineers, and architects to test your skills across scalable Java architectures, distributed systems, concurrency models, resiliency patterns, cloud-native deployments, and modern performance trade-offs.
Practice System Design MCQs with Detailed Explanations
Answer at least 12 questions to submit and verify answers.
1 Which load balancing strategy best handles uneven response times across Spring Boot instances? Medium
Correct answer:
Least Connections
Least Connections adapts to varying request durations by routing traffic to instances with fewer active connections.
2 Which caching pattern in Java microservices minimizes cache stampede during hot-key expiration? High
Correct answer:
Request coalescing (single-flight)
Request coalescing ensures only one thread recomputes and populates the cache while others wait, preventing thundering herd.
3 In a Java-based distributed system, which CAP choice is commonly preferred for user-facing services requiring high availability? Medium
Correct answer:
AP over strong consistency
Many user-facing systems favor availability and partition tolerance, accepting eventual consistency for better uptime.
4 Which Java concurrency primitive best supports high-throughput non-blocking pipelines in modern services? Medium
Correct answer:
CompletableFuture with async execution
CompletableFuture enables non-blocking composition of async tasks, improving throughput under load.
5 Which JVM-level tuning primarily reduces GC pause impact for latency-sensitive services? High
Correct answer:
Using low-latency collectors like ZGC/Shenandoah
Low-latency collectors are designed to minimize pause times, which is crucial for tail-latency sensitive systems.
6 Which resiliency pattern prevents cascading failures in Java microservices? Medium
Correct answer:
Circuit Breaker
Circuit breakers fail fast when dependencies are unhealthy, preventing resource exhaustion and cascading failures.
7 Which messaging pattern improves decoupling and scalability between Java services? Medium
Correct answer:
Event-driven messaging
Event-driven messaging decouples producers and consumers, improving scalability and fault tolerance.
8 Which design choice best improves write scalability in a high-throughput Java service storing time-series data? High
Correct answer:
Sharding by time or key
Sharding distributes writes across nodes, improving throughput and reducing contention.
9 Which approach reduces tail latency in fan-out Java services calling multiple downstream dependencies? High
Correct answer:
Parallel async calls with timeouts and hedging
Parallel async calls with timeouts and optional hedging reduce tail latency caused by slow dependencies.
10 Which data access pattern reduces load on primary databases in read-heavy Java applications? Medium
Correct answer:
Read replicas with cache
Read replicas combined with caching offload reads from the primary, improving scalability.
11 Which pattern ensures exactly-once effect processing semantics at the application level in Java consumers? High
Correct answer:
Idempotent handlers with deduplication
Idempotent processing with deduplication ensures repeated deliveries do not cause duplicated side effects.
12 Which approach best prevents connection pool exhaustion in high-QPS Java services? High
Correct answer:
Backpressure and bulkheads with bounded pools
Bounded pools with bulkheads and backpressure prevent resource exhaustion and cascading failures.
13 Which storage choice best supports horizontally scalable session management in Spring Boot? Medium
Correct answer:
External distributed cache for sessions
Externalizing sessions to a distributed cache enables horizontal scaling without session loss.
14 Which consistency model is typically acceptable for feed or notification systems built in Java microservices? Medium
Correct answer:
Eventual consistency
Eventual consistency is often acceptable for feeds/notifications where slight delays are tolerable.
15 Which Java I/O model scales better for high-concurrency network servers? Medium
Correct answer:
Non-blocking NIO with event loops
Non-blocking I/O with event loops handles many concurrent connections with fewer threads.