1.09. Stream API и Lambda

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Filterung

List<String> names = List.of("Alice", "Bob", "Carl", "Anna");
List<String> filtered = names.stream()
    .filter(n -> n.startsWith("A"))
    .toList();
System.out.println(filtered); // [Alice, Anna]

Map (Transformation)

List<String> upper = names.stream()
    .map(String::toUpperCase)
    .toList();
System.out.println(upper); // [ALICE, BOB, CARL, ANNA]

Collectors.groupingBy

Map<Integer, List<String>> grouped = names.stream()
    .collect(Collectors.groupingBy(String::length));
System.out.println(grouped);
// {3=[Bob], 4=[Anna], 5=[Alice, Carl]}