获取流

集合 ->stream .stream()

List<String> list = new ArrayList<>();
Stream<String> stream1 = list.stream();

Set<String> set = new HashSet<>();
Stream<String> stream2 = set.stream();

Vector<String> vector = new Vector<>();
Stream<String> stream3 = vector.stream();

Map -> stream

需要将key和value拆开变成流，或者先变成entry来变成流

Map<String, String> map = new HashMap<>();
// ...
Stream<String> keyStream = map.keySet().stream();
Stream<String> valueStream = map.values().stream();
Stream<Map.Entry<String, String>> entryStream = map.entrySet().stream();
}

数组 -> stream stream.of(array)

String[] array = { "张无忌", "张翠山", "张三丰", "张一元" };
Stream<String> stream = Stream.of(array);

stream常用方法

foreach

Stream<String> stream = Stream.of("张无忌", "张三丰", "周芷若");
stream.forEach(name‐> System.out.println(name));

过滤filter

Stream<String> original = Stream.of("张无忌", "张三丰", "周芷若");
Stream<String> result = original.filter(s ‐> s.startsWith("张"))

映射map

Stream<String> original = Stream.of("10", "12", "18");
Stream<Integer> result = original.map(str‐>Integer.parseInt(str));

统计个数count

Stream<String> original = Stream.of("张无忌", "张三丰", "周芷若");
Stream<String> result = original.filter(s ‐> s.startsWith("张"));
System.out.println(result.count()); // 2

取用前几个limit

如果参数大于长度，不进行操作

Stream<String> original = Stream.of("张无忌", "张三丰", "周芷若");
Stream<String> result = original.limit(2);
System.out.println(result.count()); // 2

跳过前几个skip

如果参数大于长度，返回一个空的流

Stream<String> original = Stream.of("张无忌", "张三丰", "周芷若");
Stream<String> result = original.skip(2);
System.out.println(result.count()); // 1

流拼接concat

Stream<String> streamA = Stream.of("张无忌");
Stream<String> streamB = Stream.of("张翠山");
Stream<String> result = Stream.concat(streamA, streamB);