Java8 Stream - 来自IntStream的字节的HashSet

Question

我试图创建HashSet<Byte>的byte小号1, 2, 3, ... 9与Java 8流API.我想使用IntStream然后降级值byte就可以了.

我正在尝试变种

HashSet<Byte> nums = IntStream.range(1, 10).collect(Collectors.toSet());

HashSet<Byte> nums = IntStream.range(1, 10).map(e -> ((byte) e)).collect(Collectors.toSet());

但这些都不起作用.

Error:(34, 73) java: method collect in interface java.util.stream.IntStream cannot be applied to given types;
  required: java.util.function.Supplier<R>,java.util.function.ObjIntConsumer<R>,java.util.function.BiConsumer<R,R>
  found: java.util.stream.Collector<java.lang.Object,capture#1 of ?,java.util.Set<java.lang.Object>>
  reason: cannot infer type-variable(s) R
    (actual and formal argument lists differ in length)

我需要做的flatMap还是mapToObject？

Answer 1

您需要使用mapToObj,因为HashSet和所有泛型都需要对象

Set<Byte> nums = IntStream.range(1, 10)
    .mapToObj(e -> (byte) e)
    .collect(Collectors.toSet());