Question

这是我正在研究的问题：编写一个读取3 x 4矩阵并显示每个矩阵之和的程序列和每一行分别。

这是示例运行：逐行输入3 x 4矩阵：

1.5 2 3 4
5.5 6 7 8
9.5 1 3 1

Sum of the elements at column 0 is 16.5
Sum of the elements at column 1 is 9.0
Sum of the elements at column 2 is 13.0
Sum of the elements at column 3 is 13.0
Sum of the elements at Row 0 is: 10.5
Sum of the elements at Row 0 is: 26.5
Sum of the elements at Row 0 is: 14.5

这是我想出的代码：

package multidimensionalarrays;

public class MultidimensionalArrays {

    public static void main(String[] args) {
        double sumOfRow = 0;
        double[][] matrix = new double[3][4];
        java.util.Scanner input = new java.util.Scanner(System.in); //Scanner
        System.out.println("Enter a 3 by 4 matrix row by row: ");
        //Prompt user to enter matrix numbers
        for (int row = 0; row < matrix.length; row++) {
            for (int col = 0; col < matrix[0].length; col++) {
                matrix[row][col] = input.nextDouble();
            }
        }
        double[] sumOfCol =new double[matrix[0].length];  
        for (int i = 0; i < matrix.length; i++) { //row
            for (int j = 0; j < matrix[i].length; j++) { //column
                sumOfRow += matrix[i][j];
                sumOfCol[j] += matrix[i][j];
            }
            System.out.println("Sum of the elements at row " + row + " is: " + sumOfRow);
        }
        System.out.println("Sum of the elements at column " + col + " is: " + sumOfCol);
    }             
}

我的问题是，到最后打印列和行的总和时，它无法识别row或col变量。我一直在玩它，并且可能已经改变了几个小时，而我似乎无法正确解决这个问题，有人可以帮我解决我做错的事情吗？还不知道我是否在正确地进行列求和？

Answer 1

在您的matrix中，它是代码段double[][] matrix = new double[3][4];中的3×4矩阵。第一个索引是行索引，第二个索引是列索引。

请注意，您的double[][]矩阵是数组数组。即，matrix是由三个长度为4的数组组成的数组，按照惯例，每个子数组都可以看作是排列成一行的对象的数组。这称为行主要订单。

例如，在数组中

0 1 2 4
0 1 3 9
0 1 5 15

它实际上存储为

matrix[0]: [matrix[0][0], matrix[0][1], matrix[0][2], matrix[0][3]和[0 1 2 4]
matrix[1]: [matrix[1][0], matrix[1][1], matrix[1][2], matrix[1][3]和[0 1 3 9]
matrix[2]: [matrix[2][0], matrix[2][1], matrix[2][2], matrix[2][3]和[0 1 5 25]

这是一种更简单的算法，该算法使用循环来查找每个行和列值的值总和，但需要两次通过：

/* After the prompt code segment and sumOfCol in the main method */

    // Row (major index)
    for (int row = 0; row < matrix.length; row++) {
        int rowSum = 0;
        for (int col = 0; col < matrix[row].length; col++) {
            rowSum += matrix[row][col];
        }
        System.out.println("Sum of the elements at row " + row + " is: " + rowSum);
    }

    // Column (minor index)
    // Assuming the length of each row is the same
    for (int col = 0; col < matrix[0].length; col++) {
        int colSum = 0;
        for (int row = 0; row < matrix.length; row++) {
            colSum += matrix[row][col];
        }
        System.out.println("Sum of the elements at col " + col + " is: " + colSum);
    }

输出为

Enter a 3 by 4 matrix row by row: 
0 1 2 4
0 1 3 9
0 1 5 15
Sum of the elements at row 0 is: 7
Sum of the elements at row 1 is: 13
Sum of the elements at row 2 is: 21
Sum of the elements at col 0 is: 0
Sum of the elements at col 1 is: 3
Sum of the elements at col 2 is: 10
Sum of the elements at col 3 is: 28

Answer 2

计算行数的变量在打印行总和时称为i。

对于列总和，您需要另一个循环来逐个打印它们。

如何使用Java分别汇总2D数组的行和列？

2 个答案: