Convert ArrayList to Double Array in java [duplicate]

Question

How to Convert ArrayList to Double Array in Java6?

 List lst = new ArrayList();
 double[] dbl=null;
 lst.add(343.34);
 lst.add(432.34);

How convert above list to array?

Answer 1

You can directly convert the List to an Array of the wrapper class. Try the following:

List<Double> lst = new ArrayList<>();
Double[] dblArray = new Double[lst.size()];
lst.add(343.34);
lst.add(432.34);
dblArray = lst.toArray(dblArray);

Answer 2

List<Number> lst = new ArrayList<>();
Collections.addAll(lst, 3.14, -42);
double[] dbl = lst.stream()
    .map(Number::cast) // Or possibly Double::cast when List lst.
    .mapToDouble(Number::doubleValue)
    .toArray();

List<Double> lst = new ArrayList<>();
Collections.addAll(lst, 3.14, -42.0);
double[] dbl = lst.stream()
    .mapToDouble(Double::doubleValue)
    .toArray();

The mapToDouble transforms an Object holding Stream to a DoubleStream of primitive doubles.

Answer 3

With this you will make the list and add what you like. Then make the array the same size and fill front to back.

public static void main(String[] args){
        List lst = new ArrayList();
        lst.add(343.34);
        lst.add(432.34);
        System.out.println("LST " + lst);

        double[] dbl= new double[lst.size()];
        int iter = 0;
        for (Object d: lst
             ) {
            double e = (double) d;
            dbl[iter++] = e;
        }
        System.out.println("DBL " + Arrays.toString(dbl));
    }

Result: LST [343.34,432.34] DBL [343.34,432.34]