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Topic
Collection contracts, generic type safety, functional transformations, stream execution, aggregation, and Optional boundaries.
Practice items tagged with Collections, Generics & Streams.
Explains collectors as terminal reduction strategies and composes grouping, mapping, counting, and summary operations.
Explains stream sources, lazy intermediate operations, terminal execution, short-circuiting, encounter order, and single use.
Explains Java HashMap lookup through hashing, buckets, equality, collisions, resizing, and stable keys without implementation trivia.
Applies upper and lower bounded wildcards to producer and consumer APIs while explaining their limits.
Chooses a Java collection by the behavior the code needs: ordering, duplicates, membership, lookup keys, and iteration.
Makes duplicate-key behavior explicit through validation, merge policies, grouping, and deterministic map selection.