android java what is a long[ ][ ]?

Question

I need to do the chiSquaredTest. I'm using the Apache Commons Math library but not sure what is a long[][] what the difference to a long[] ? Here is the method description :

  public double chiSquareTest(long[][] counts)
                 throws NullArgumentException,
                        DimensionMismatchException,
                        NotPositiveException,
                        MaxCountExceededException

Returns the observed significance level, or p-value, associated with a chi-square test of independence based on the input counts array, viewed as a two-way table.

The rows of the 2-way table are count[ 0 ], ... , count[count.length - 1]

Preconditions:

• List item All counts must be ≥ 0.
• The count array must be rectangular (i.e. all count[ i ] subarrays must have the same length).
• The 2-way table represented by counts must have at least 2 columns and at least 2 rows.
• If any of the preconditions are not met, an IllegalArgumentException is thrown.

Parameters:

• counts - array representation of 2-way table

Returns:

• p-value

Answer 1

long[] - it is one dimensional array.

long[] array = new long[4];

/* result of that array
{0, 0, 0, 0}
*/

long[][] - it is array of arrays / two dimensional array.

long[][] array2 = new long[4][];
array2[0] = new long[1];
array2[1] = new long[2];
array2[2] = new long[4];
array2[3] = new long[3];

/* result of that array
{
    {0},
    {0, 0},
    {0, 0, 0, 0},
    {0, 0, 0},
}
*/

or it can be like that:

long[][] array = new long[4][4];

/* result of that array
{
    {0, 0, 0, 0},
    {0, 0, 0, 0},
    {0, 0, 0, 0},
    {0, 0, 0, 0},
}
*/

For more examples go to this link.