灌装使用流多维数组 [英] Filling a Multidimensional Array using a Stream

问题描述

我是新来的Java 8，目前未能充分掌握数据流，将有可能填补使用Stream功能操作数组？这是我将如何与循环标准做一个例子code：

I'm new to Java 8 and currently failing to grasp Streams fully, is it possible to fill an array using the Stream functional operations? This is an example code of how I would do it with a standard for loop:

public static void testForLoop(){
    String[][] array = new String[3][3];
    for (int x = 0; x < array.length; x++){
        for (int y = 0; y < array[x].length; y++){
            array[x][y] = String.format("%c%c", letter(x), letter(y));
        }
    }               
}

public static char letter(int i){
    return letters.charAt(i);
} 

如果有可能的话用流会怎么办？如果可能的话，是很方便（性能和可读性明智）？

If it is possible how would I do it using Stream? If it is possible, is it convenient (performance and readability wise)?

推荐答案

在这里，你有一个产生的，而不是数组修改previously定义变量的解决方法：

Here you have a solution that produces the array instead of modifying a previously defined variable:

String[][] array = 
    IntStream.range(0, 3)
             .mapToObj(x -> IntStream.range(0, 3)
                                     .mapToObj(y -> String.format("%c%c", letter(x), letter(y)))
                                     .toArray(String[]::new))
             .toArray(String[][]::new);

如果你想使用并行流，那么，以避免副作用，如一个变量（数组或对象）的修改，这是非常重要的。这可能会导致竞争条件或其他并发问题。您可以阅读<一个更多有关href=\"https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html\">java.util.stream包文档 - 见的非干扰的无国籍行为的和的副作用的部分。

If you want to use parallel streams then it's very important to avoid side effects like modifications of a variable (array or object). It might lead to race conditions or other concurrency issues. You can read more about that in java.util.stream package documentation - see Non-interference, Stateless behaviors and Side-effects sections.

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