Java Homework

They want me to multiply a matrix using arrays..
So the matrix is an array of arrays?
I'm a bit confused..

if i say
double[][] matrix;
how do i tell which [] has the rows and which has the columns? or is that for me to define?

>>41
As soon as I read that it has anything to do with .NET I realized that it was a retarded idea.

Also the example looks like C++.