[java] Fastest way to get the first n elements of a List into an Array

What is the fastest way to get the first n elements of a list stored in an array?

Considering this as the scenario:

int n = 10;
ArrayList<String> in = new ArrayList<>();
for(int i = 0; i < (n+10); i++)
  in.add("foobar");

Option 1:

String[] out = new String[n];
for(int i = 0; i< n; i++)
    out[i]=in.get(i);

Option 2:

String[] out = (String[]) (in.subList(0, n)).toArray();

Option 3: Is there a faster way? Maybe with Java8-streams?

Use: Arrays.copyOf(yourArray,n);

It mostly depends on how big n is.

If n==0, nothing beats option#1 :)

If n is very large, toArray(new String[n]) is faster.

Option 3

Iterators are faster than using the get operation, since the get operation has to start from the beginning if it has to do some traversal. It probably wouldn't make a difference in an ArrayList, but other data structures could see a noticeable speed difference. This is also compatible with things that aren't lists, like sets.

String[] out = new String[n];
Iterator<String> iterator = in.iterator();
for (int i = 0; i < n && iterator.hasNext(); i++)
    out[i] = iterator.next();

Assumption:

list - List<String>

Using Java 8 Streams,

• to get first N elements from a list into a list,

  List<String> firstNElementsList = list.stream().limit(n).collect(Collectors.toList());

• to get first N elements from a list into an Array,

  String[] firstNElementsArray = list.stream().limit(n).collect(Collectors.toList()).toArray(new String[n]);