# 配列、ストリーム、コレクションの変換 ~ int編 ~

2023/03/29に公開

## 扱うもの

• 配列
• `int[]`
• `Integer[]`
• ストリーム
• `IntStream`
• `Stream<Integer>`
• コレクション
• `List<Integer>`
• `Set<Integer>`

## `int[]` -> `IntStream`

``````int[] arr = new int[]{1,2,3};
// その1
IntStream intStream = IntStream.of(arr);
// その2
IntStream intStream = Arrays.stream(arr);
``````

## `IntStream` -> `int[]`

``````IntStream intStream = IntStream.of(1,2,3);
int[] arr = intStream.toArray();
``````

## `IntStream` -> `Stream<Integer>`

``````IntStream intStream = IntStream.of(1,2,3);
Stream<Integer> intStream.boxed();
``````

## `Stream<Integer>` -> `IntStream`

``````Stream<Integer> stream = Stream.of(1,2,3);
IntStream intStream = stream.mapToInt(Integer::intValue);
``````

## `Stream<Integer>` -> `Integer[]`

``````Stream<Integer> stream = Stream.of(1,2,3);
Integer[] arr = stream.toArray(Integer[]::new);
``````

## `Integer[]` -> `Stream<Integer>`

``````Integer[] arr = new Integer[]{1,2,3};
// その1
Stream<Integer> stream = Stream.of(arr);
// その2
Stream<Integer> stream = Arrays.stream(arr);
``````

## `List<Integer>` -> `Stream<Integer>`

``````List<Integer> list = Arrays.asList(1,2,3);
Stream<Integer> stream = list.stream();
``````

## `Stream<Integer>` -> `List<Integer>`

``````Stream<Integer> stream = Stream.of(1,2,3);
List<Integer> list = stream.collect(Collectors.toList());
``````

## `Stream<Integer>` -> `Set<Integer>`

``````Stream<Integer> stream = Stream.of(1,2,3);
Set<Integer> set = stream.collect(Collectors.toSet());
``````

## `Set<Integer>` -> `Stream<Integer>`

``````Set<Integer> set = new HashSet<Integer>(Arrays.asList(1,2,3));
Stream<Integer> stream = set.stream();
``````

## `List<Integer>` -> `Set<Integer>`

``````List<Integer> list = Arrays.asList(1,2,3);
Set<Integer> set = new HashSet<Integer>(list);
``````

## `Set<Integer>` -> `List<Integer>`

``````Set<Integer> set = new HashSet<Integer>(Arrays.asList(1,2,3));
List<Integer> list = new ArrayList<Integer>(set)
``````

## `List<Integer>` -> `Integer[]`

``````List<Integer> list = Arrays.asList(1,2,3);
Integer[] arr = list.toArray(new Integer[0]);
``````

## `Integer[]` -> `List<Integer>`

``````Integer[] arr = new Integer[]{1,2,3};
List<Integer> list = Arrays.asList(arr);
``````