Perform operation on n random distinct elements from Collection using Streams API

Question

I\'m attempting to retrieve n unique random elements for further processing from a Collection using the Streams API in Java 8, however, without much or any luck.

Mor

Answer 1

List collection = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
int n = 4;
Random random = ThreadLocalRandom.current();

random.ints(0, collection.size())
        .distinct()
        .limit(n)
        .mapToObj(collection::get)
        .forEach(System.out::println);

This will of course have the overhead of the intermediate set of indexes and it will hang forever if n > collection.size().

If you want to avoid any non-constatn overhead, you'll have to make a stateful Predicate.