将Streams与原语数据类型和相应的包装器一起使用 [英] Using Streams with primitives data types and corresponding wrappers

问题描述

在玩Java8的Streams-API时，我偶然发现了以下内容：

While playing around with Java8's Streams-API, I stumbled over the following:

将原始包装器classe对象数组转换为 Stream 我只需要调用 Stream.of（array）。但是要转换原始数据类型的数组，我必须从相应的包装器（类）流类调用 .of（array）（< - 听起来很傻） 。

To convert an array of primitive wrapper classe objects into a Stream I just have to call Stream.of(array). But to convert an array of primitive data types, I have to call .of(array) from the corresponding wrapper (class) stream class (<-- that sounds silly).

一个例子：

final Integer[] integers = {1, 2, 3};
final int[]     ints     = {1, 2, 3};


Stream.of(integers).forEach(System.out::println); //That works just fine

Stream.of(ints).forEach(System.out::println);     //That doesn't

IntStream.of(ints).forEach(System.out::println);  //Have to use IntStream instead

我的问题（s ）：
这是为什么？这与例如 Arrays.asList（）的行为也适用于包装类数组？

My question(s): Why is this? Does this correlate to e.g. the behaviour of Arrays.asList() which also just works for wrapper class arrays?

推荐答案

Java 8流框架具有通用的 Stream< T> 作为元素的对象，以及三个基本流 IntStream ， LongStream ， DoubleStream 。如果您使用原语，请使用后者之一，在您的情况下 IntStream 。

Java 8 stream framework has a generic Stream<T> for objects as elements, and three primitive streams IntStream, LongStream, DoubleStream for the main three primitives. If you work with primitives, use one of those latter, in your case IntStream.

查看图片：

背后的原因是：

1. Java泛型不能与原始类型一起使用：可能只有 List< Integer> 和 Stream< Integer> ，但不是 List< int> 和 Stream< int>

1. Java generics cannot work with primitive types: it is possible to have only List<Integer> and Stream<Integer>, but not List<int> and Stream<int>

当 Java Collections 框架，它仅针对类引入，所以如果你想要一个列表 int s，你必须将它们包装到整数秒。这很昂贵！

When the Java Collections framework was introduced, it was introduced only for classes, so if you want to have a List of ints, you have to wrap them to Integers. This is costly!

当 Java Streams 框架，他们决定绕过这个开销和并行与面向类的流（使用泛型机制），他们介绍了三个所有库函数的额外集合，专为最重要的原始类型设计： int ， long ， double 。

When the Java Streams framework was introduced, they decided to get around this overhead and in parallel with the "class-oriented" streams (using the generics mechanism), they introduced three extra sets of all the library functions, specifically designed for the most important primitive types: int, long, double.

此处还可以看到一个奇妙的解释： https://stackoverflow.com/a/22919112/2886891

And see also a marvelous explanation here: https://stackoverflow.com/a/22919112/2886891

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