Question

这是这里的第一篇文章，如果我的问题在这里没有达到要求的标准，请原谅我。

我编写了一段代码，它从两个独立的文件中获取两个矩阵的输入，并执行乘法并将数据输出到一个新文件。

它为2x3或3x3矩阵提供了完美的输出。如果我输入4x4矩阵，我得到数组索引超出绑定运行时异常。我动态创建索引

时，我不明白这个原因

我在第40行得到一个超出绑定异常的数组索引。

我收到错误。

！[Snipet] [2]

列出项目

public class MM {




private BufferedReader br;
private int sum = 0;
private final static String matrixA="matrixA.txt"; 
private final static String matrixB="matrixB.txt";

public static void main(String[] args) {
    new MM().MathMultiplicationValues(matrixA, matrixB);
}

private void MathMultiplicationValues(String mat1, String mat2) {
    try {
        br = new BufferedReader(new FileReader(mat1));          

        String line;
        int mat1rows = 0, mat1cols = 0, mat2rows = 0, mat2cols = 0;
        while ((line = br.readLine()) != null) {
            mat1cols = line.split(" ").length + 1;
            mat1rows++;
        }
        br.close(); // To close file
        br = new BufferedReader(new FileReader(mat2)); // to read input from file.
        while ((line = br.readLine()) != null) {
            mat2cols = line.split(" ").length + 1;
            mat2rows++;
        }
        int[][] mat1vals = new int[mat1rows ][mat1cols ]; 
    int[][] mat2vals = new int[mat2rows ][mat2cols ]; 
        br.close();
        br = new BufferedReader(new FileReader(mat1));
        for (int i = 1; i < mat1rows + 1; i++) {
            line = br.readLine();
            String[] colvals = line.split(" ");
            for (int j = 1; j < mat1cols; j++) {
                mat1vals[i][j] = Integer.parseInt(colvals[j - 1]);

            }

        }


        br.close();
        br = new BufferedReader(new FileReader(mat2));
        for (int i = 1; i < mat2rows + 1; i++) {
            line = br.readLine();
            String[] colvals = line.split(" ");
            for (int j = 1; j < mat2cols; j++) {
                mat2vals[i][j] = Integer.parseInt(colvals[j - 1]);

            }


        }

        br.close();
        if ((mat1cols-1) == mat2rows) { 
            int[][] resltmat = new int[mat1rows + 1][mat2cols + 1];
            for (int i = 1; i < mat1rows + 1; i++) { //Loop does matrix multiplication. 
                for (int j = 1; j < mat1cols; j++) {
                    for (int k = 0; k < mat2rows + 1; k++)
                        sum = sum + mat1vals[i][k] * mat2vals[k][j];
                    resltmat[i][j] = sum;
                    sum = 0;
                }
            }

            final PrintWriter pw = new PrintWriter("Answer.txt"); //Creates a new file called Matrix Answer. 
            for (int i = 1; i < mat1rows + 1; i++) 
            {

                for (int j = 1; j < mat2cols; j++) {
                    pw.print(resltmat[i][j] + " "); // Writes the output to file the file called MatrixAnswer

                }
                pw.println();

            }
            pw.close();
        } else // If no of columns not equal to rows control passes to else block. 
            System.out.println("Multiplication of Matrix is not possible because columns are not equal to rows");

    } catch (Exception e) {
        e.printStackTrace();

    }
}

}

Answer 1

可能是因为这个

for (int i = 1; i < mat1rows + 1; i++) {
    line = br.readLine();
    String[] colvals = line.split(" ");
    for (int j = 1; j < mat1cols; j++) {
        mat1vals[i][j] = Integer.parseInt(colvals[j - 1]);

    }

}

i = mat1rows在最后一次迭代，即OOB。将for (int i = 1; i < mat1rows + 1; i++)更改为for (int i = 1; i < mat1rows; i++)

Answer 2

正如您在分配中使用的那样，结果矩阵的维度为mat1rows x mat2cols。因此，在resltmat[i][j]的计算中，索引i已绑定mat1rows（检查），而索引j具有上限mat2cols（失败）。因此，将j的范围从mat1cols更改为mat2cols。

矩阵乘法返回数组索引超出范围的错误

2 个答案: