How to get Array from Arraylist

Question

I have the following data structure in Linear_Programming class .

ArrayList<ArrayList<Double>> constraint_temp  ;
ArrayList<Double> B_value_temp;
ArrayList<Double> obj_func ;

I want to pass this object to Simplex class constructor by the following code .

 Simplex smlpx = new Simplex(constraint_temp, B_value_temp,obj_func);

The prototype for constructor of Simplex method is as follows :

 public Simplex(double[][] A, double[] b, double[] c);

So I need a way to convert the arraylist to array . How can I do this ? Please suggest me a way .

I think main problem in first 2d array. Need some manual work. — disable1992, Jul 07 '14 at 06:18
It returns oject[] type . And what is the issue of 2d array ? — osimer pothe, Jul 07 '14 at 06:18
`toArray()` also has an overloaded method to accept the array and populate it, did you check it? — TheLostMind, Jul 07 '14 at 06:18
possible duplicate of [Convert ArrayList to String \[\]](http://stackoverflow.com/questions/5374311/convert-arrayliststring-to-string) — Raedwald, Jul 07 '14 at 06:31
Raedwald , Please look at the question . Help is needed because of 2d array . — osimer pothe, Jul 07 '14 at 06:33

score 3 · Accepted Answer · answered Jul 07 '14 at 06:27

First, write a method to convert a List<Double> to a double[] -

private static double[] fromList(List<Double> al) {
  double[] out = new double[al.size()];
  for (int i = 0;i < al.size(); i++) {
    out[i] = al.get(i);
  }
  return out;
}

Then the complicated version is the two-dimensional argument a,

double[][] a = new double[constraint_temp.size()][];
for (int i = 0; i < a.length; i++) {
  a[i] = fromList(constraint_temp.get(i));
}
double[] b = fromList(B_value_temp);
double[] c = fromList(obj_func);
Simplex smlpx = new Simplex(a,b,c);

How to get Array from Arraylist

1 Answers1