I'm trying to convert an ArrayList containing Integer objects to primitive int[] with the following piece of code, but it is throwing compile time error. Is it possible to convert in Java?
List<Integer> x = new ArrayList<Integer>();
int[] n = (int[])x.toArray(int[x.size()]);
If you are using java-8 there's also another way to do this.
int[] arr = list.stream().mapToInt(i -> i).toArray();
What it does is:
Stream<Integer>
from the listIntStream
by mapping each element to itself (identity function), unboxing the int
value hold by each Integer
object (done automatically since Java 5)int
by calling toArray
You could also explicitly call intValue
via a method reference, i.e:
int[] arr = list.stream().mapToInt(Integer::intValue).toArray();
It's also worth mentioning that you could get a NullPointerException
if you have any null
reference in the list. This could be easily avoided by adding a filtering condition to the stream pipeline like this:
//.filter(Objects::nonNull) also works
int[] arr = list.stream().filter(i -> i != null).mapToInt(i -> i).toArray();
Example:
List<Integer> list = Arrays.asList(1, 2, 3, 4);
int[] arr = list.stream().mapToInt(i -> i).toArray(); //[1, 2, 3, 4]
list.set(1, null); //[1, null, 3, 4]
arr = list.stream().filter(i -> i != null).mapToInt(i -> i).toArray(); //[1, 3, 4]