eclipse 如何在二维数组中添加元素

how to add elements in a 2d array

提问by lawtonhself

I just want to know how this program works, and why the answer is 14. here is the code:

我只想知道这个程序是如何工作的，为什么答案是 14。这是代码：

public class extra {
public static void main(String[] args){
    int[][] table = {{1,2,3},{4,5,6},{7,8,9}};
    int sum = 0;
    for( int i = 2; i > 0; i-- ) 
              sum += table[i][3-i];
              System.out.println(sum);

}

}

}

I understand the way the matrix is set up

我了解矩阵的设置方式

123

123

456

456

789

789

but what is i in this problem, because I thought it was the number of rows, but since it is in a for loop, does it mean that i is the number in the matrix? Also how do the [i][3-i] come in to affect? The answer is 14, and I just want to know how it is 14.

但是这个问题中的 i 是什么，因为我认为它是行数，但是由于它在 for 循环中，这是否意味着 i 是矩阵中的数字？另外 [i][3-i] 是如何产生影响的？答案是14，我只想知道14是怎么来的。

回答by Patricia Shanahan

It is only summing part of a diagonal, specifically table[2][1]which is 8, and table[1][2]which is 6.

它只是对角线的一部分求和，具体来说table[2][1]哪个是 8，table[1][2]哪个是 6。

The easiest way to see what is going on is to add an output statement in the loop:

查看发生了什么的最简单方法是在循环中添加一个输出语句：

for (int i = 2; i > 0; i--) {
  sum += table[i][3 - i];
  System.out.println(i + " " + (3 - i) + " " + table[i][3 - i]);
}

回答by dawrutowicz

your program takes table[2][1] (value of 8) and table[1][2] (value of 6) elements, sums them and prints as output (value of 14)

您的程序采用 table[2][1]（值为 8）和 table[1][2]（值为 6）元素，将它们相加并打印为输出（值为 14）

regarding your question in a title your main method should be more like this:

关于标题中的问题，您的主要方法应该更像这样：

public static void main(String[] args) {
    int[][] table = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    int sum = 0;

    System.out.println("Before\n");

    for (int i = 0; i < table.length; i++) {
        for (int j = 0; j < table[i].length; j++) {
            sum += table[i][j];
            System.out.printf("Sum after %d iteration: %d\n", i + j + 1, sum);
        }
    }

    System.out.println("\nIn total: " + sum);
}

i + j + 1 is a sum of current iteration which is sum of both axises, and since Java has 0-based indexed tables, it is increased by 1

i + j + 1 是当前迭代的总和，它是两个轴的总和，并且由于 Java 具有基于 0 的索引表，因此增加了 1

Hope it helps!

希望能帮助到你！

回答by Rhyzomatic

i, in itself, does not correspond directly to anything in the matrix. It is just the name of the variable that the for loop changes each time it loops.

i本身并不直接对应于矩阵中的任何内容。for 循环每次循环时更改的只是变量的名称。

The [i][3-i]is how the iinteracts with table. On the first round of the for loop, the iwill be equal to 2. Thus, sumwill be increased by table[2][1], which is the 3rd row and the 2nd column of the matrix, which has a value of 8.

这[i][3-i]就是 与i交互的方式table。在 for 循环的第一轮中，thei将等于 2。因此，sum将增加table[2][1]，这是矩阵的第 3 行第 2 列，其值为8。

On the second round of the for loop, the for loop, the iwill be equal to 1. Thus, sumwill be increased by table[1][2], which is the 2nd row and the 3rd column of the matrix, which has a value of 6.

在 for 循环的第二轮 for 循环中，thei将等于 1。因此，sum将增加table[1][2]，即矩阵的第 2 行第 3 列，其值为6。

Therefore, sumwill be equal to 8+6=14.

因此，sum将等于 8+6=14。

回答by Martin M J

What the for loop does is as follows:

for 循环的作用如下：

1. i= 2. Enter loop.
2. Add table[2][3-2]to sum. Sum is now 8, because table[2][1]= 8.
3. Decrement iby 1.
4. i= 1. Enter loop.
5. Add table[1][3-1]to sum. Sum is now 14, because table[1][2]= 6.
6. Decrement iby 1.
7. i= 0. 0 is not greater than 0, so we exit the loop. The sum became 14.

1. i= 2. 进入循环。
2. 添加table[2][3-2]到总和。Sum 现在是 8，因为table[2][1]= 8。
3. 减i1。
4. i= 1. 进入循环。
5. 添加table[1][3-1]到总和。Sum 现在是 14，因为table[1][2]= 6。
6. 减i1。
7. i= 0。0不大于0，所以我们退出循环。总和变成了14。

---

---

Two-dimensional arrays like int[][] tablehave two indexes. One for the "outer" array (or rows), and one for the "inner" ones (columns).

二维数组就像int[][] table有两个索引。一个用于“外部”数组（或行），一个用于“内部”数组（列）。

Let's use int[][] table = {{1,2,3},{4,5,6},{7,8,9}};from your code as an example:

让我们以int[][] table = {{1,2,3},{4,5,6},{7,8,9}};您的代码为例：

table[1][2]: 1 means we should look in the array at index 1, which is {4,5,6}. 2 means we should look at {4,5,6}'s index 2, which is 6. In other words table[1][2] == 6.

table[1][2]: 1 意味着我们应该在索引 1 处查看数组，即{4,5,6}. 2 表示我们应该查看{4,5,6}的索引 2，即6。换句话说table[1][2] == 6。

table[2][0]: 2 means we should look in the array at index 2, which is {7,8,9}. 0 means we should look at {7,8,9}'s index 0, which is 7.

table[2][0]: 2 意味着我们应该查看索引 2 处的数组，即{7,8,9}. 0 表示我们应该查看{7,8,9}的索引 0，即7。

回答by btgui

for (int i = 2; i > 0; i--)

so starting at 2 it checks if i is greater than zero loops once then i-- subtracts 1 check again still greater than 0 loops again then subtracts 1 again checks if greater than 0 now 0 it is not greater than 0 so stops looping //thus loops 2 times

所以从 2 开始它检查 i 是否大于零循环一次然后 i-- 再次减去 1 检查仍然大于 0 再次循环然后再次减去 1 检查是否大于 0 现在 0 它不大于 0 所以停止循环 //因此循环2次

//[0] = 1st [1] = 2nd [2] = third ...

//counting in code starts at zero not 1 so and array of 3 counts a the spaces 0,1,2

int sum = 0;//sum starts at zero

//using the value of i translates as such

sum += table[2][3-2];//[2][1]this is 3rd group 2nd part so sum += 8
//then
sum += table[1][3-1];//[1][2]this is 2nd group 3rd part so sum += 6

0 + 8 + 6 = 14

0 + 8 + 6 = 14

回答by Naji Kadri

Here's how to add elements in a 2D array in a easy way. Firstwhen you initialize a 2D array think of the first brackets [ ] as a column and the second bracket [ ] as column rows. For example: int[][] num = new int[10][5]which means 10 columns and 5 rows.

下面介绍如何以简单的方式在 2D 数组中添加元素。 首先，当您初始化二维数组时，将第一个括号 [ ] 视为列，将第二个括号 [ ] 视为列行。例如：int[][] num = new int[10][5]这意味着 10 列和 5 行。

If you want to fill all the elements in a 2D array you must use two forloops:

如果要填充二维数组中的所有元素，则必须使用两个for循环：

int[][] num = new int[10][5];

for (int i =0; i < num.length;i++ ) {
     for (int x=0; x < num[0].length;i++) { //we used num[0] because we need the length of the rows not the columns
           num[i][x] = //any value you want to assign
          }
 }