배열 ↔ 리스트 형변환 모음

int[] → Set<Integer>

: int[] nums = {1, 2, 3, 4, 5}가 있을 때,

Set<Integer> set = Arrays.stream(nums).boxed().collect(Collectors.toSet());

Set<Integer> set = IntStream.of(nums).boxed().collect(Collectors.toSet());

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int[] → Integer[]

: int[] nums = {1, 2, 3, 4, 5}가 있을 때,

Integer[] boxed = IntStream.of(nums).boxed().toArray(Integer[]::new);

Integer[] boxed = Arrays.stream(nums).boxed().toArray(Integer[]::new);

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int[] → HashSet<Integer>

: int[] nums = {1, 2, 3, 4, 5}가 있을 때,

HashSet<Integer> hashset = IntStream.of(nums).boxed().collect(Collectors.toCollection(HashSet::new));

HashSet<Integer> hashset = Arrays.stream(nums).boxed().collect(Collectors.toCollection(HashSet::new));

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Integer[] → HashSet<Integer>

: Integer[] nums = {1, 2, 3, 4, 5}가 있을 때,

Set<Integer> set = new HashSet<>(Arrays.asList(nums));

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int[] → List<Integer>

: int[] nums = {1, 2, 3, 4, 5}가 있을 때,

List<Integer> list = Arrays.stream(nums).boxed().collect(Collectors.toList());

• Java 16+ 부터는:

List<Integer> list = Arrays.stream(nums).boxed().toList();

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List<Integer> → int[]

: List<Integer> list = Arrays.asList(1, 2, 3, 4, 5) 가 있을 때,

int[] primitive = list.stream().maptoInt(Integer::intValue).toArray();

// Commons Collections(Apache)를 이용한 방법:
import org.apache.commons.lang3.ArrayUtils;
int[] primitive = ArrayUtils.toPrimitive(list.toArray(new Integer[0]));

// Guava API를 이용한 방법:
import com.google.common.primitives.Ints;
int[] primitive = Ints.toArray(list);

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