Java 将 Streams 与原始数据类型和相应的包装器一起使用
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原文地址: http://stackoverflow.com/questions/23007422/
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Using Streams with primitives data types and corresponding wrappers
提问by ifloop
While playing around with Java8's Streams-API, I stumbled over the following:
在使用 Java8 的 Streams-API 时，我偶然发现了以下内容：
To convert an array of primitive wrapper classe objects into a StreamI 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).
要将原始包装器类对象的数组转换为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.of(array)从相应的包装器（类）流类中调用（<-- 听起来很傻）。
An example:
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
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?
我的问题：这是为什么？这是否与例如它的行为Arrays.asList()也仅适用于包装类数组有关？
采纳答案by Honza Zidek
Java 8 stream framework has a generic Stream<T>for objects as elements, and three primitive streams IntStream, LongStream, DoubleStreamfor the main three primitives. If you work with primitives, use one of those latter, in your case IntStream.
爪哇8流框架有一个通用Stream<T>的对象作为元素，以及三个原始流IntStream，LongStream，DoubleStream对三个主要的原语。如果您使用原语，请在您的情况下使用后者之一IntStream。
See the picture:
看图：
What lies behind is that:
背后的原因是：
Java genericscannot work with primitive types: it is possible to have only
List<Integer>andStream<Integer>, but notList<int>Stream<int>When the Java Collectionsframework was introduced, it was introduced only for classes, so if you want to have a
Listofints, you have to wrap them toIntegers. This is costly!When the Java Streamsframework was introduced, they decided to get around this overhead and in parallelwith 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.
Java 泛型不能与原始类型一起使用：可能只有
List<Integer>andStream<Integer>，但没有List<int>Stream<int>当Java集合引入框架，据介绍只有上课，所以如果你想拥有
List的intS，你必须给他们换到Integer秒。这是昂贵的！当Java Streams框架被引入时，他们决定绕过这个开销并与“面向类”的流并行（使用泛型机制），他们引入了三个额外的所有库函数集，专门为最重要的原始类型：
int,long,double.
And see also a marvelous explanation here: https://stackoverflow.com/a/22919112/2886891
并在这里看到一个奇妙的解释：https: //stackoverflow.com/a/22919112/2886891
