Top 50 collections Interview Questions
The most frequently asked collections questions across all roles and companies, ranked by real interview frequency. Updated daily.
Implement a thread-safe collection with atomic batch updates and deterministic ordering.
NiCECount every character in a string using the built-in Counter and return frequency totals.
ChewySort an integer array in ascending order and return the sorted elements as a List.
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Explains how HashMap uses hashing, buckets, collision handling, resizing, and equals/hashCode to store and retrieve entries.
Goldman Sachs Asset & Wealth ManagementAAlgoSecCompare ArrayList and Map by storage model, access pattern, ordering, and appropriate use cases.
Accion LabsCompare Java ArrayList and LinkedList internals, operation costs, memory behavior, and appropriate use cases.
Compare Java Collection storage and traversal with Stream pipeline processing, including laziness, reuse, memory, and parallel execution.
DeloitteCalculate net loss on a defaulted credit balance after applying the expected collections recovery rate.
Capital OneExplain core Java concepts and produce an aggregated SQL access summary using joins.
SaviyntRank active HSBC employees by division and return every employee tied for the highest or second-highest salary.
HsbcReturn cardholders whose 2025 approved transaction total is at least 1000 across multiple transaction records.
Mastercard