如何收集DoubleStream到List

Question

我有以下代码：

Stream.of("1,2,3,4".split(",")).mapToDouble(Double::valueOf).collect(Collectors.toList());

我要returnList<Double>.

此代码无法编译。

我看到错误：

Error:(57, 69) java: method collect in interface java.util.stream.DoubleStream cannot be applied to given types;
  required: java.util.function.Supplier<R>,java.util.function.ObjDoubleConsumer<R>,java.util.function.BiConsumer<R,R>
  found: java.util.stream.Collector<java.lang.Object,capture#1 of ?,java.util.List<java.lang.Object>>
  reason: cannot infer type-variable(s) R
    (actual and formal argument lists differ in length)

如何解决这个问题？

Answer 1

您可以使用 boxed(). This maps a DoubleStream (Stream of primitive doubles, as returned by mapToDouble) 到 Stream<Double>。

Stream.of("1,2,3,4".split(",")).mapToDouble(Double::parseDouble).boxed().collect(Collectors.toList());

请注意，我更改了 Double::valueOf to Double::parseDouble：这可以防止 Double.valueOf 返回的 Double 被拆箱为原始 double。

但是你为什么一开始就使用 mapToDouble？您可以像这样使用 map：

Stream.of("1,2,3,4".split(",")).map(Double::valueOf).collect(Collectors.toList());

如何收集DoubleStream到List

How to collect DoubleStream to List

java

collect

java-8

java-stream