java从2D double[]数组获取子数组

Question

我试图从double[][]3x3矩阵中得到一个子数组（用于计算行列式）。我一直收到ArrayIndexOutOfBoundsException

知道为什么吗

public double[][] get2DSubArray(double[][] largeArray, int rowStartIndex, int rowEndIndex, int columnStartIndex, int columnEndIndex) {
    double[][] subArray = new double[rowEndIndex-rowStartIndex+1][columnEndIndex-columnStartIndex+1];
    for (int row = rowStartIndex; row < rowEndIndex; row++) {
        subArray[row] = Arrays.copyOfRange(largeArray[row], columnStartIndex, columnEndIndex);
    }
    return subArray;
}

Answer 1

看起来它与数组初始化有关，传递给该方法的array似乎不是3x3。例如，以下情况不会产生例外：

public static void main(String[] args) throws IOException {
    double[][] array = new double[][]{{1d,1d,1d},{2d,2d,2d},{3d,3d,3d}};
    double[][] subArray = get2DSubArray(array, 1, 2, 1, 2);
    for(double[] arrayElement : subArray){
        for(double number : arrayElement){
            System.out.println(number);
        }
    }
}

public static double[][] get2DSubArray(double[][] largeArray, int rowStartIndex, int rowEndIndex, int columnStartIndex,
        int columnEndIndex) {
    double[][] subArray = new double[rowEndIndex - rowStartIndex + 1][columnEndIndex - columnStartIndex + 1];
    for (int row = rowStartIndex; row < rowEndIndex; row++) {
        subArray[row] = Arrays.copyOfRange(largeArray[row], columnStartIndex, columnEndIndex);
    }
    return subArray;
}

更新

尽管上述解决方案不会产生异常，但也不会产生正确的输出。主要原因如下：

• Arrays.copyOfRange方法的第三个参数是独占的，所以我们必须传递columnEndIndex+1才能让它工作
• 对于提供的参数集，for循环只执行一次，而它应该至少执行两次
• 我们需要将Arrays.copyOfRange分配给subArray[row]，而不是将其分配给subArray[<zero based index>]

以下解决方案确实有效：

public double[][] get2DSubArray(double[][] largeArray, int rowStartIndex, int rowEndIndex, int columnStartIndex,
        int columnEndIndex) {
    double[][] subArray = new double[rowEndIndex - rowStartIndex + 1][columnEndIndex - columnStartIndex + 1];
    int index = 0;
    for (int row = rowStartIndex; row <= rowEndIndex; row++) {
        subArray[index++] = Arrays.copyOfRange(largeArray[row], columnStartIndex, columnEndIndex+1);
    }
    return subArray;
}