如何将 Java 8 Stream 转换为数组？

How to convert a Java 8 Stream to an Array?

提问by

What is the easiest/shortest way to convert a Java 8 Streaminto an array?

将 Java 8Stream转换为数组的最简单/最短的方法是什么？

采纳答案by skiwi

The easiest method is to use the toArray(IntFunction<A[]> generator)method with an array constructor reference. This is suggested in the API documentation for the method.

最简单的方法是使用toArray(IntFunction<A[]> generator)带有数组构造函数引用的方法。方法的API 文档中建议了这一点。

String[] stringArray = stringStream.toArray(String[]::new);

What it does is find a method that takes in an integer (the size) as argument, and returns a String[], which is exactly what (one of the overloads of) new String[]does.

它所做的是找到一个方法，它接受一个整数（大小）作为参数，并返回一个String[]，这正是（的重载之一）new String[]所做的。

You could also write your own IntFunction:

你也可以自己写IntFunction：

Stream<String> stringStream = ...;
String[] stringArray = stringStream.toArray(size -> new String[size]);

The purpose of the IntFunction<A[]> generatoris to convert an integer, the size of the array, to a new array.

的目的IntFunction<A[]> generator是将一个整数（数组的大小）转换为一个新数组。

Example code:

示例代码：

Stream<String> stringStream = Stream.of("a", "b", "c");
String[] stringArray = stringStream.toArray(size -> new String[size]);
Arrays.stream(stringArray).forEach(System.out::println);

Prints:

印刷：

a
b
c

回答by Ida Buci?

If you want to get an array of ints, with values form 1 to 10, from a Stream, there is IntStream at your disposal.

如果您想从 Stream 中获取一个整数数组，其值从 1 到 10，则可以使用 IntStream。

Here we create a Stream with a Stream.of method and convert an Stream to an IntStream using a mapToInt. Then we can call IntStream's toArray method.

在这里，我们使用 Stream.of 方法创建一个 Stream，并使用 mapToInt 将一个 Stream 转换为 IntStream。然后我们可以调用 IntStream 的 toArray 方法。

Stream<Integer> stream = Stream.of(1,2,3,4,5,6,7,8,9,10);
//or use this to create our stream 
//Stream<Integer> stream = IntStream.rangeClosed(1, 10).boxed();
int[] array =  stream.mapToInt(x -> x).toArray();

Here is the same thing, without the Stream, using only the IntStream

这是同样的事情，没有 Stream，只使用 IntStream

int[]array2 =  IntStream.rangeClosed(1, 10).toArray();

回答by Thomas Pliakas

You can create a custom collector that convert a stream to array.

您可以创建一个将流转换为数组的自定义收集器。

public static <T> Collector<T, ?, T[]> toArray( IntFunction<T[]> converter )
{
    return Collectors.collectingAndThen( 
                  Collectors.toList(), 
                  list ->list.toArray( converter.apply( list.size() ) ) );
}

and a quick use

和快速使用

List<String> input = Arrays.asList( ..... );

String[] result = input.stream().
         .collect( CustomCollectors.**toArray**( String[]::new ) );

回答by Sagar Mal Shankhala

     Stream<Integer> stream = Stream.of(1, 2, 3, 4, 5, 6);

     Integer[] integers = stream.toArray(it->new Integer[it]);

回答by Bachiri Taoufiq Abderrahman

You can convert a java 8 stream to an array using this simple code block:

您可以使用这个简单的代码块将 java 8 流转换为数组：

 String[] myNewArray3 = myNewStream.toArray(String[]::new);

But let's explain things more, first, let's Create a list of string filled with three values:

但是让我们更详细地解释一下，首先，让我们创建一个填充了三个值的字符串列表：

String[] stringList = {"Bachiri","Taoufiq","Abderrahman"};

Create a stream from the given Array :

从给定的 Array 创建一个流：

Stream<String> stringStream = Arrays.stream(stringList);

we can now perform some operations on this stream Ex:

我们现在可以对这个流执行一些操作，例如：

Stream<String> myNewStream = stringStream.map(s -> s.toUpperCase());

and finally convert it to a java 8 Array using these methods:

最后使用以下方法将其转换为 java 8 数组：

1-Classic method (Functional interface)

1-经典方法（Functional interface）

IntFunction<String[]> intFunction = new IntFunction<String[]>() {
    @Override
    public String[] apply(int value) {
        return new String[value];
    }
};


String[] myNewArray = myNewStream.toArray(intFunction);

2 -Lambda expression

2 -Lambda 表达式

 String[] myNewArray2 = myNewStream.toArray(value -> new String[value]);

3- Method reference

3- 方法参考

String[] myNewArray3 = myNewStream.toArray(String[]::new);

Method reference Explanation:

方法参考说明：

It's another way of writing a lambda expression that it's strictly equivalent to the other.

这是编写 lambda 表达式的另一种方式，它严格等同于另一个。

回答by Kunda

Using the toArray(IntFunction<A[]> generator)method is indeed a very elegant and safe way to convert (or more correctly, collect) a Stream into an array of the same type of the Stream.

使用该toArray(IntFunction<A[]> generator)方法确实是一种非常优雅且安全的方式，可以将 Stream 转换（或更准确地说，是收集）Stream 为与 Stream 类型相同的数组。

However, if the returned array's type is not important, simply using the toArray()method is both easier andshorter. For example:

但是，如果返回数组的类型并不重要，那么简单地使用该toArray()方法既简单又简短。例如：

    Stream<Object> args = Stream.of(BigDecimal.ONE, "Two", 3);
    System.out.printf("%s, %s, %s!", args.toArray());

回答by Danail Tsvetanov

Convert text to string array where separating each value by comma, and trim every field, for example:

将文本转换为字符串数组，其中用逗号分隔每个值，并修剪每个字段，例如：

String[] stringArray = Arrays.stream(line.split(",")).map(String::trim).toArray(String[]::new);

回答by raja emani

You can do it in a few ways.All the ways are technically the same but using Lambda would simplify some of the code. Lets say we initialize a List first with String, call it persons.

您可以通过几种方式来实现。所有方式在技术上都是相同的，但使用 Lambda 会简化一些代码。假设我们首先用字符串初始化一个列表，称之为人。

List<String> persons = new ArrayList<String>(){{add("a"); add("b"); add("c");}};
Stream<String> stream = persons.stream();

Now you can use either of the following ways.

现在您可以使用以下任一方式。

1. Using the Lambda Expresiion to create a new StringArray with defined size.

   String[] stringArray = stream.toArray(size->new String[size]);

2. Using the method reference directly.

   String[] stringArray = stream.toArray(String[]::new);

1. 使用 Lambda 表达式创建具有定义大小的新 StringArray。

   String[] stringArray = stream.toArray(size->new String[size]);

2. 直接使用方法引用。

   String[] stringArray = stream.toArray(String[]::new);

回答by Raj N

Stream<Integer> stream = Stream.of(1, 2, 3, 4, 5, 6);

int[] arr=   stream.mapToInt(x->x.intValue()).toArray();

回答by Sma Ma

import java.util.List;
import java.util.stream.Stream;

class Main {

    public static void main(String[] args) {
        // Create a stream of strings from list of strings
        Stream<String> myStreamOfStrings = List.of("lala", "foo", "bar").stream();

        // Convert stream to array by using toArray method
        String[] myArrayOfStrings = myStreamOfStrings.toArray(String[]::new);

        // Print results
        for (String string : myArrayOfStrings) {
            System.out.println(string);
        }
    }
}

Try it out online: https://repl.it/@SmaMa/Stream-to-array

在线试用：https: //repl.it/@SmaMa/Stream-to-array