Java 和 C# 中的多维数组

发布于 2024-10-22 05:17:14 字数 417 浏览 1 评论 0原文

在 C# 中，有两种创建多维数组的方法。

int[,] array1 = new int[32,32];

int[][] array2 = new int[32][];
for(int i=0;i<32;i++) array2[i] = new int[32];

我知道第一个方法在内部创建一个一维数组，第二个方法创建一个数组的数组（访问速度较慢）。

然而在 Java 中，没有 [,] 这样的东西，我看到多维数组是这样声明的：

int[][] array3 = new int[32][32];

由于这种语法在 C# 中是非法的，并且 Java 没有 int[,]，所以我想知道这是否等同于 array1 ？或者它仍然是数组的数组？

原文

In C# there are 2 ways to create mutlidimensional arrays.

int[,] array1 = new int[32,32];

int[][] array2 = new int[32][];
for(int i=0;i<32;i++) array2[i] = new int[32];

I know that the first method creates a 1-dimensional array internally, and that the second method creates an array of arrays (slower access).

However in Java, there is no such thing as [,], and I see multidimensional arrays declared like this:

int[][] array3 = new int[32][32];

Since such syntax is illegal in C#, and Java has no int[,], I'm wondering if this is equivilant to array1? Or is it still an array of arrays?

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您的好友蓝忘机已上羡 2024-10-29 05:17:14

它仍然是一个数组的数组。只是在 C# 中，您必须在循环中创建每个子数组。所以这个 Java:

// Java
int[][] array3 = new int[32][32];

相当于这个 C#:

// C#
int[][] array3 = new int[32][];
for (int i = 0; i < array3.Length; i++)
{
    array3[i] = new int[32];
}

（正如 Slaks 所说，锯齿状数组在 .NET 中通常比矩形数组更快。但它们在内存方面效率较低。）

It's still an array of arrays. It's just that in C# you'd have to create each subarray in a loop. So this Java:

// Java
int[][] array3 = new int[32][32];

is equivalent to this C#:

// C#
int[][] array3 = new int[32][];
for (int i = 0; i < array3.Length; i++)
{
    array3[i] = new int[32];
}

(As Slaks says, jagged arrays are generally faster in .NET than rectangular arrays. They're less efficient in terms of memory though.)

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花海 2024-10-29 05:17:14

你错了；锯齿状（嵌套）数组速度更快。（CLR 针对它们进行了优化）

Java 不支持真正的多维数组；这是一个锯齿状数组。
Java 语法自动创建所有内部数组；在 C# 中，这需要一个单独的循环。

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葵雨 2024-10-29 05:17:14

因为人们关心 .NET 中多维数组与交错数组的性能，所以我实现了一些测试，并对 8k x 8k 元素的结果进行了基准测试：

测试是：

多维 2D 数组
索引向后的多维 (y第一）
使用 GetLength(x) 而不是整数绑定的多维交错
与向后索引
交错
一维（大小 x 大小）与索引相乘
一维与增量索引

结果：

one <> Elapsed Time: 0.543558s
two <> Elapsed Time: 0.8911516s
three <> Elapsed Time: 0.8908123s
four <> Elapsed Time: 1.1367238s
five <> Elapsed Time: 0.3039648s
six <> Elapsed Time: 0.8110969s
seven <> Elapsed Time: 0.2629394s

为了好玩，我也在 WP7 模拟器上运行它们，并得到类似的数字。

测试函数的代码位于此处。

Because people were concerned about the performance of multi-dimension vs staggered arrays in .NET, I implemented a few tests and benchmarked the results on 8k by 8k elements:

The tests were:

Multi-dimensional 2D array
Multi-dimensional with indices backwards (y first)
Multi-dimensional with GetLength(x) instead of integer bound
Staggered with backwards indicies
Staggered
One dimensional (size x size) with multiplication in index
One dimensional with increment index

And the results:

one <> Elapsed Time: 0.543558s
two <> Elapsed Time: 0.8911516s
three <> Elapsed Time: 0.8908123s
four <> Elapsed Time: 1.1367238s
five <> Elapsed Time: 0.3039648s
six <> Elapsed Time: 0.8110969s
seven <> Elapsed Time: 0.2629394s

For fun I ran them on the WP7 emulator as well, and got similar numbers.

Code of the test function is here.

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倾城°AllureLove 2024-10-29 05:17:14

在 Java 中，您正在声明一个数组的数组。

您可以通过以下代码看到这一点：

int[][] arrOfArr = new int[5][];
arrOfArr[0] = new int[5];
arrOfArr[1] = new int[1];
arrOfArr[2] = new int[9];
...

int[][] arr = new int[3][3]; 只是以下代码的简写：

int[][] arr = new int[3][];
arr[0] = new int[3];
arr[1] = new int[3];
arr[2] = new int[3];

In Java you are declaring an array of arrays.

You can see this by the following code:

int[][] arrOfArr = new int[5][];
arrOfArr[0] = new int[5];
arrOfArr[1] = new int[1];
arrOfArr[2] = new int[9];
...

int[][] arr = new int[3][3]; is just shorthand for:

int[][] arr = new int[3][];
arr[0] = new int[3];
arr[1] = new int[3];
arr[2] = new int[3];

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只是我以为 2024-10-29 05:17:14

我正在将一些 Java 代码转换为 C# - 这是我如何制作锯齿状数组

    //Java
    private static int grad3[][] = {{1,1,0},{-1,1,0},{1,-1,0},{-1,-1,0},{1,0,1},{-1,0,1},{1,0,-1},{-1,0,-1},{0,1,1},{0,-1,1},{0,1,-1},{0,-1,-1}};

    //C#
    private static int[,] grad3setup = { { 1, 1, 0 }, { -1, 1, 0 }, { 1, -1, 0 }, { -1, -1, 0 }, { 1, 0, 1 }, { -1, 0, 1 }, { 1, 0, -1 }, { -1, 0, -1 }, 
                                  { 0, 1, 1 }, { 0, -1, 1 }, { 0, 1, -1 }, { 0, -1, -1 } };

    private static int[][] grad3
    {
        get
        {
            int[][] grad3 = new int[12][];
            for (int i = 0; i < grad3.Length; i++)
            {
                grad3[i] = new int[3] { grad3setup[i, 0], grad3setup[i, 1], grad3setup[i, 2] };
            }
            return grad3;
        }
    }

I was translating some Java code to C# - here is how I did the Jagged array

    //Java
    private static int grad3[][] = {{1,1,0},{-1,1,0},{1,-1,0},{-1,-1,0},{1,0,1},{-1,0,1},{1,0,-1},{-1,0,-1},{0,1,1},{0,-1,1},{0,1,-1},{0,-1,-1}};

    //C#
    private static int[,] grad3setup = { { 1, 1, 0 }, { -1, 1, 0 }, { 1, -1, 0 }, { -1, -1, 0 }, { 1, 0, 1 }, { -1, 0, 1 }, { 1, 0, -1 }, { -1, 0, -1 }, 
                                  { 0, 1, 1 }, { 0, -1, 1 }, { 0, 1, -1 }, { 0, -1, -1 } };

    private static int[][] grad3
    {
        get
        {
            int[][] grad3 = new int[12][];
            for (int i = 0; i < grad3.Length; i++)
            {
                grad3[i] = new int[3] { grad3setup[i, 0], grad3setup[i, 1], grad3setup[i, 2] };
            }
            return grad3;
        }
    }

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