New to Java

im trying to make a sudoku puzzle but having trouble with the arrays, ive got two arrays

int [][] actual = new int [9][9];
    String [][] possible = new String [9][9];

part of my code im trying to generate a sudoku board, this is the part of the error in

public void possVals(int col, int row)
	{
		if(possible[col][row].equals(""))
		{
			str = "123456789";
		}
		else str = possible[col][row];
		
		for(r = 1; r < 9; r++)
		{
			if(actual[col][r] != 0)
			{
				str = str.Replace(actual[col][r].toString(), "");
			}
		}

could some one tell me how to fix my error of 'cannot invoke toString on the primitive type int' please