Question

So I’m to write a simple thing which reads an input file till EOF reached – the file consists of int-double pairs. I’m to calculate the average of all the elements in the second array and finally have both sets of data stored in respective arrays of primitive data types.

Of course the task is easy so the question isn’t directly about it – rather, about the array part. As I don’t know how many pairs I’ll have to store, I use two ArrayLists to store it. The spec strictly points that in the end, however, both ints and doubles have to be store in primitive arrays – and here comes my question. Is there some faster way to do this than just copying the ArrayList to a primitive type array? I can’t use an array from the beginning since I don’t know the size or even an upper bound and using toArray() also woulnd’t work as I have to have primitive int[] and double[] in the end, not objects of Integer[] and Double[].

Answer 1

You should be able to cast from a Double to a primitive double.

Something like:

    ArrayList<Double> test = new ArrayList<Double>();
    //Get your values into the ArrayList here.

    double[] values = new double[test.size()];
    for(int i = 0; i < test.size(); i++){
        values[i] = test.get(i).doubleValue();
    }

As far as I know, there isn’t more a “nice” way of doing it than just copying it straight across…