Trouble filling 2D array with values obtained from method

Question

I'm having trouble filling a matrix with values I get by iterating through a method. I want to use a 3x3 matrix and then fill it with the values I obtain by iterating my method from 0 to 8. My idea was a for-loop but it does not work unfortunately. I would be glad if someone could help or has a link where I can look that up.

int[][] matrix = new int[3][3];

for (int i = 0; i < matrix.length; i++){
  for (int j = 0; j < matrix[i].length; j++){
    for(int a = 0; a < 9; a++) {
      matrix[i][j] = fields.get(a).getSign().getFieldValue();
    }       
  }
}

Answer 1

Correct me if im wrong. the way i understood your question was you want to fill the matrix like this:

012
345
678

in that case you can do the first 2 forloops and add some maths, to get the correct numbers on every position:

int[][] matrix = new int[3][3];

for (int i = 0; i < matrix.length; i++) {
  for (int j = 0; j < matrix[i].length; j++) {
    matrix[i][j] = i * matrix[i].length + j;
  }
}

the way this works is for every row (i) you multiplay the rownumber by the rows length (the ammount of columns) and add the current column to it

Answer 2

To iterate through a two dimensional field (eg a matrix), you can use two for loops:

int dimension = 3;
int [][] matrix = new int [dimension][dimension];

for (int i = 0; i < dimension; i++){
   for ( int j = 0; j < dimension; j++){
      matrix[i][j] = fields.get(i).get(j);
   }
}

I don't exactly know how you want to retrieve the values, but your current call looks suspicious to say the least :-) It will simply assign the same value to all ints in column j .

Answer 3

If you simulate your loop, this is what it looks like

i -> 0
    j -> 0
        matrix[0][0] -> loop over all values from field

this way you would be putting the fields.get(8) into each index in your matrix.

@Alan's answers show how to properly loop and fill a 2d matrix from a 1d matrix