Streams API

A Stream is a single-use lazy pipeline, not a collection. Intermediate operations build the pipeline; a terminal operation consumes it.

Declarative transformation

List<String> result = names.stream()
    .filter(name -> !name.isBlank())
    .map(String::trim)
    .distinct()
    .sorted()
    .toList();

Use map for one-to-one transformation, flatMap for nested sources, and reduce/collectors for aggregation. Avoid stateful side effects and modifying the source. Parallel streams require associative operations, splittable data, sufficient work, and careful common-pool impact; measure before enabling. Streams holding I/O resources require try-with-resources.