CODEWITHSUNDEEP
javajava-8java-stream
NDavis
NDavis

Reputation: 1227

Why does java stream.count() return a long?

Why doesn't a stream.count() return an int?

I understand that I can easily convert the long to an int by casting,

return (int) players.stream().filter(Player::isActive).count();

but why would a java stream.count() return a long instead of an int?

Upvotes: 43

Views: 40768

Answers (3)

Greg Osgood
Greg Osgood

Reputation: 241

This statement

players.stream().filter(Player::isActive).count();

is equivalent to:

players.stream().filter(Player::isActive).collect(Collectors.counting());

This still returns a long because Collectors.counting() is implemented as 

reducing(0L, e -> 1L, Long::sum)

Returning an int can be accomplished with the following:

players.stream().filter(Player::isActive).collect(Collectors.reducing(0, e -> 1, Integer::sum));

This form can be used in groupingBy statement

Map<Player, Integer> playerCount = players.stream().filter(Player::isActive).collect(Collectors.groupingBy(Function.identity(), Collectors.reducing(0, e -> 1, Integer::sum)));

Upvotes: 24

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726539

When Java came out in early 1996, common PCs had 8 to 16 Mb of memory. Since both arrays and collections were closely tied to memory size, using int to represent element counts seemed natural, because it was sufficient to address an array of ints that is 4Gb in size - a size gigantic even for hard drives in 1996, let alone RAM. Hence, using long instead of int for collection sizes would seem wasteful at the time.

Although int size may be a limiting factor at times, Java designers cannot change it to long, because it would be a breaking change.

Unlike Java collections, streams could have potentially unlimited number of elements, and they carry no compatibility considerations. Therefore, using long with its wider range of values seems like a very reasonable choice.

Upvotes: 25

Eugene
Eugene

Reputation: 120848

Well simply because it's the biggest 64-bit primitive value that java has. The other way would be two counts:

countLong/countInt

and that would look really weird.

int fits in a long, but not the other way around. Anything you want to do with int you can fit in a long, so why the need to provide both?

Upvotes: 23

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