Error Handling and Defensive Programming Questions

Covers designing and implementing defensive, fault tolerant code and system behaviors to prevent and mitigate production failures. Topics include input validation and sanitization, null and missing data handling, overflow and boundary protections, exception handling and propagation patterns, clear error reporting and structured logging for observability, graceful degradation and fallback strategies, retry and backoff policies and idempotency for safe retries. Also address concurrency and synchronization concerns, resource and memory management to avoid exhaustion, security related input checks, and how to document and escalate residual risks. Candidates should discuss pragmatic trade offs between robustness and complexity, show concrete defensive checks and assertions, and describe test strategies for error paths including unit tests and integration tests and how monitoring and operational responses tie into robustness.

HardTechnical

0 practiced

You are paged for a production issue: multiple services experience increasing 5xx errors after a deploy. Provide a prioritized incident response plan: immediate mitigation steps to reduce customer impact, how to gather diagnostics safely, rollback vs patch decision criteria, and post-incident actions to prevent recurrence.

HardTechnical

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You see intermittent `ConcurrentModificationException` in a Java service processing high-volume events. Propose a sequence of diagnostic steps to reproduce and fix the issue, explain why it happens, and present at least two fixes with their performance implications.

MediumTechnical

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Propose a test strategy to cover retry and fallback logic for a microservice that depends on a flaky external API. Include unit tests, contract tests, integration tests, and chaos experiments. Explain how to avoid nondeterministic failures in CI while still getting high confidence.

EasyTechnical

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Describe three practical strategies to avoid `NullPointerException` (or equivalent null dereference) in a large Java codebase. For each strategy, explain the trade-offs, backwards-compatibility concerns, and how you would enforce it across the team (lint rules, code review, runtime checks).

MediumTechnical

0 practiced

Implement an exponential backoff with full jitter retry helper in Python: signature `retry(func, max_attempts=5, base_delay=0.1, max_delay=10.0)` where `func` is a callable that may raise exceptions. Ensure delays are randomized, that the function is safe for concurrent use, and document when this pattern is appropriate.

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