用Java初始化带有流的2d数组 [英] Initializing 2d array with streams in Java

问题描述

我有以下课程：

public class MyClass{
    //...
    public MyClass(int x, int y){
        //...
    }
}

现在，我需要使用项目初始化2d数组

Now, I need to initialize 2d-array with the items

int rows;
int cols;
//initializing rows and cols
MyClass[][] arr = new MyClass[rows][cols];
//how to initialize arr[x][y] with 
//new MyClass(x, y) with streams API

我查看了这个示例，但它在我的案例中不起作用。他们使用一个 IntStream

I looked at this example but it doesn't work in my case. They use a single IntStream

问题： 当然我可以使用嵌套for循环，但我认为它现在是旧式的并且考虑不好。那么如何应用流api并以 Java8 方式启动它？

推荐答案

Streams不太擅长跟踪索引，这是您需要的。所以你可以像@NicolasFilotto那样滥用它们，或者以更简单的方式：

Streams are not very good at keeping track of index, which you need here. So you can abuse them like @NicolasFilotto proposes, or in a simpler way:

MyClass[][] array = new MyClass[rows][cols];
IntStream.range(0, rows)
         .forEach(r -> IntStream.range(0, cols)
                                .forEach(c -> array[r][c] = new MyClass(r, c)));

你甚至可以让它看起来更实用，摆脱 forEach 和变异部分：

You could even make it look more functional and get rid of the forEach and the mutation part:

MyClass[][] array = IntStream.range(0, rows)
                .mapToObj(r -> IntStream.range(0, cols)
                                        .mapToObj(c -> new MyClass(r, c))
                                        .toArray(MyClass[]::new))
                .toArray(MyClass[][]::new);

但老实说， for循环不会过时：

But honestly, for loops are not obsolete:

for (int r = 0; r < rows; r++) {
  for (int c = 0; c < cols; c++) {
    array[r][c] = new MyClass(r, c);
  }
}

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