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lounah
Asked:2020-09-07 03:11:50 +0000 UTC2020-09-07 03:11:50 +0000 UTC

Java，ArrayIndexOutOfBoundsException：3

  • 772

你好。需要实现矩阵乘法，代码如下：

public class MatrixMultiplier {

    private  int[][] transportMatrix(int[][] a) {
        int[][] b = new int[a.length][a.length];
        for (int i = 0; i < a.length; ++i)
            for (int j = 0; j < a.length; ++j) {
                b[i][j] = a[j][i];
            }
        return b;
    }

    public int[][] multiply(int[][] mA, int[][] mB) {
        int mSize = mA.length;
        mB = transportMatrix(mB);
        int nSize = mB[0].length;
        int o = mB.length;
        int[][] mResult = new int[mSize][nSize];

        for (int i = 0; i < mSize; i++) {
            for (int j = 0; j < nSize; j++) {
                for (int k = 0; k < o; k++) {
                    System.out.print(i + " " + j);
                    mResult[i][j] += mA[i][k] * mB[k][j];
                }
            }
        }

        for (int i = 0; i < mResult.length; i++) {
            for (int j = 0; j < mResult[0].length; j++) {
                System.out.format("%6d ", mResult[i][j]);
            }
            System.out.println();
        }

        return mResult;
    }
}

public class MatrixMultiply {

    private static int[][] mA;
    private static int[][] mB;
    private static int[][] mResult;

    public static void main(String[] args) {
        MatrixMultiplier matrixMultiplier = new MatrixMultiplier();
         mA = new int[][] {{5,3,2},
                          {3,1,0},
                          {1,4,1},
                          {8,2,1}};

         mB = new int[][] {{5,6,2},
                          {3,1,0},
                          {1,4,1},
                          {8,2,1},
                          {3,1,1}};

        mResult = new int[mA.length][mB[0].length];
        mResult = matrixMultiplier.multiply(mA, mB);
    }

}

结果异常：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
at matrix.MatrixMultiplier.transportMatrix(MatrixMultiplier.java:8)
at matrix.MatrixMultiplier.multiply(MatrixMultiplier.java:15)
at matrix.MatrixMultiply.main(MatrixMultiply.java:23)

为什么？

java

1 个回答

  1. Best Answer

    在错误中，矩阵转置函数和乘法循环中存在问题，您对为元素设置哪些索引感到困惑。在这里，与您的比较，我删除了错误：

        public class MatrixMultiply {
    private static int[][] mA,
                           mB,
                           mResult;

    public static void main(String[] args) {
        MatrixMultiplier matrixMultiplier = new MatrixMultiplier();
        mA = new int[][]{{5, 3, 2},
                         {3, 1, 0},
                         {1, 4, 1},
                         {8, 2, 1}};

        mB = new int[][]{{5, 6, 2},
                         {3, 1, 0},
                         {1, 4, 1},
                         {8, 2, 1},
                         {3, 1, 1}};

        mResult = new int[mA.length][mB.length];

        System.out.println("Первая матрица");
        matrixMultiplier.print(mA);

        System.out.println("Вторая матрица");
        mB = matrixMultiplier.transportMatrix(mB);
        matrixMultiplier.print(mB);

        System.out.println("Результирующая матрица");
        mResult = matrixMultiplier.multiply(mA, mB);
        matrixMultiplier.print(mResult);
    }
}

class MatrixMultiplier{
    public  int[][] transportMatrix(int[][] a) {
        int[][] b = new int[a[0].length][a.length];
        for (int i = 0; i < a[0].length; i++)
            for (int j = 0; j < a.length; j++) {
                b[i][j] = a[j][i];
            }
        return b;
    }

    public int[][] multiply(int[][] mA, int[][] mB) {
        int mSize = mA.length;
        int nSize = mB[0].length;
        int o = mB.length;
        int[][] mResult = new int[mSize][nSize];

        for (int i = 0; i < mSize; i++) {
            for (int j = 0; j < nSize; j++) {
                for (int k = 0; k < o; k++) {
                    mResult[i][j] += mA[i][k] * mB[k][j];
                }
            }
        }
        return mResult;
    }

    public void print(int[][] m) {
        for (int i = 0; i < m.length; i++) {
            for (int j = 0; j < m[0].length; j++) {
                System.out.format("%6d ", m[i][j]);
            }
            System.out.println();
        }
    }
}
    • 3

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