Java8中Stream 的一些用法
数据结构和数据准备
@Data@AllArgsConstructor@NoArgsConstructorstatic class StreamItem {Integer id;String name;Boolean sex;}List<StreamItem> list = Lists.newArrayList(new StreamItem(1, "a", true), new StreamItem(2, "b", false),new StreamItem(3, "c", true), new StreamItem(1, "d", false), new StreamItem(4, "e", true));
map
List<String> list2 = list.stream().map(StreamItem::getName).collect(Collectors.toList());System.out.println(list2);[a, b, c, d, e]
groupingBy
Map<Integer, List<StreamItem>> list2 = list.stream().collect(Collectors.groupingBy(StreamItem::getId));System.out.println(list2);{1=[StreamStudy.StreamItem(id=1, name=a, sex=true), StreamStudy.StreamItem(id=1, name=d, sex=false)], 2=[StreamStudy.StreamItem(id=2, name=b, sex=false)],3=[StreamStudy.StreamItem(id=3, name=c, sex=true)], 4=[StreamStudy.StreamItem(id=4, name=e, sex=true)]}
toMap
Map<Integer, String> list2 = list.stream().collect(Collectors.toMap(StreamItem::getId, StreamItem::getName, (k1, k2) -> k2));System.out.println(list2);{1=d, 2=b, 3=c, 4=e}
filter
List<StreamItem> list2 = list.stream().filter(StreamItem::getSex).collect(Collectors.toList());System.out.println(list2);[StreamStudy.StreamItem(id=1, name=a, sex=true), StreamStudy.StreamItem(id=3, name=c, sex=true), StreamStudy.StreamItem(id=4, name=e, sex=true)]
sum
int sum = list.stream().mapToInt(StreamItem::getId).sum();System.out.println(sum);sum = list.stream().map(StreamItem::getId).reduce(Integer::sum).get();System.out.println(sum);sum = list.stream().map(StreamItem::getId).reduce(0, Integer::sum);System.out.println(sum);BigDecimal bigDecimal = list.stream().map(streamItem -> new BigDecimal(streamItem.getId())).reduce(BigDecimal.ZERO, BigDecimal::add);System.out.println(bigDecimal);11111111
参考
使用Stream快速对List进行一些操作
Java8之Consumer、Supplier、Predicate和Function攻略
版权声明：本文为eaglelihh原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。