Sorting a List in parallel without creating a temporary array in Java 8

Question

Java 8 provides java.util.Arrays.parallelSort, which sorts arrays in parallel using the fork-join framework. But there\'s no corresponding Collections.parallelSort

Answer 1

By combining the existing answers I came up with this code.
This works if you are not interested in creating a custom List class and if you don't bother to create a temporary array (Collections.sort is doing it anyway).
This uses the initial list and does not create a new one as in the parallelStream solution.

// Convert List to Array so we can use Arrays.parallelSort rather than Collections.sort.
// Note that Collections.sort begins with this very same conversion, so we're not adding overhead
// in comparaison with Collections.sort.
Foo[] fooArr = fooLst.toArray(new Foo[0]);

// Multithread the TimSort. Automatically fallback to mono-thread when size is less than 8192.
Arrays.parallelSort(fooArr, Comparator.comparingStuff(Foo::yourmethod));

// Refill the List using the sorted Array, the same way Collections.sort does it.
ListIterator i = fooLst.listIterator();
for (Foo e : fooArr) {
    i.next();
    i.set((Foo) e);
}