原文 http://renchx.com/java8-stream2/
将结果收集到 Map 中 - @Test
- public void getResultToMap() {
- Stream<String> stream = Stream.of("a", "b", "c", "da", "asdass");
- Map<String, Integer> map = stream.collect(Collectors
- .toMap(String::toString, String::length));
- System.out.println(map);
- }
分组和分片
groupingBy 会产生一个值为列表的 map 对象。 - @Test
- public void groupBy() {
- Stream<Locale> stream = Stream.of(Locale.getAvailableLocales());
- Map<String, List<Locale>> map = stream.collect(Collectors.groupingBy(Locale::getCountry));
- Map<String, Set<Locale>> map2 = stream.collect(Collectors.groupingBy(Locale::getCountry,
- Collectors.toSet()));
- Map<String, Long> map3 = stream.collect(Collectors.groupingBy(Locale::getCountry,
- Collectors.counting()));// 返回根据国家分组的语言个数的map
- // Map<String, Long> map4 =
- // citys.collect(Collectors.groupingBy(City::getState,
- // Collectors.summingLong(City::getPopulation)));
- // 模拟计算每个州下的城市人口数
- // Map<String, City> map5 =
- // citys.collect(Collectors.groupingBy(City::getState,
- // Collectors.maxBy(Compartor.comparing(City::getPopulation))));
- // 映射每个州人口最多的城市
- Map<String, Set<String>> map6 = stream.collect(
- Collectors.groupingBy(Locale::getDisplayCountry,
- Collectors.mapping(Locale::getDisplayLanguage, Collectors.toSet())));
- System.out.println(map);
- }
Stream api 提供了原始类型流： - @Test
- public void baseStream() {
- IntStream intStream = IntStream.of(1, 2, 3);
- int[] values = { 2, 3, 4, 5, 6, 7, 8, 9, 0, 1 };
- IntStream intStream2 = Arrays.stream(values, 2, 5);
- IntStream intStream3 = IntStream.range(0, 10);// 不包含上限
- IntStream intStream4 = IntStream.rangeClosed(0, 10);// 包含上限
- Stream<String> stream = Stream.of("a", "asd", "2s");
- IntStream intStream5 = stream.mapToInt(String::length);
- Stream<Integer> stream2 = intStream2.boxed();// 原生流转换成对象流
- intStream2.forEach(System.out::println);
- }
【参考资料】
写给大忙人看的Java SE 8
|
