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?
3 Answers
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);
2 Comments
Nonika
no need of specifying size. just
dblArray =lst.toArray(new Double[0])
Kayaman
@Nonika if you do not specify the size (or the size isn't correct), a new array will be created automatically. This does not usually matter, but it's still a significant difference in that your code will create 2 arrays, whereas the code in the answer only creates one.
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.
Comments
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]
ListlikeList<Double>... it will be messy if you don'tDouble[]) is not a double array (double[]) - those are different types. Which one are you trying to convert to?