Problem accessing multidimensional array length and fields - arrays

Question

Here is code to test a multidimensional array
public class Multiarraytest {
public int size_main = 5;
public int size_aux = 20;
Multiarraytest() {
float[][] float_mul = new float[size_main][size_aux];
}
void init_int(Multiarraytest mul) {
int i, j = 0;
while(i < mul.length) {
while(j < mul[i].length) {
mul[i][j] = (i + (j/10));
j++;
}
i++;
}
}
public static void main(String[] args) {
}
}
But
here are the results of javac Multiarraytest.java.
error: cannot find symbol While(i < mul.length)
^
symbol: variable length
location: variable mul of type Multiarraytest
error: array required, but Multiarraytest found while(j < mul[i].length
^
error: array required, but Multiarraytest found mul[i][j] = (i + (j/10));
I have not found what's going wrong.
mul is a 2 dimensional array
mul.length should give the length of the first array
mul[1] should lead to the array nested in the first case of mul
mul[1].length should give the length of the array nested in the first case of mul
mul[1][2] should give access to read/write of the second case of the array nested in the first case of mul.
Where have I made a mistake?
This is a cut down version of what I was doing but same errors are reported. I read tutorial and close copy-cut it. Except it's a float multidimensional array instead of int multidimensional array and I try to fill it in a loop instead at the initializing time.