CODEWITHSUNDEEP
javajava-8java-stream
T Tse
T Tse

Reputation: 846

Why does Collectors.counting reduce into a long?

From https://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html#counting--:

public static <T> Collector<T,?,Long> counting()

Returns a Collector accepting elements of type T that counts the number of input elements. If no elements are present, the result is 0.

Implementation Requirements:

This produces a result equivalent to:

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

Why does this Collector collect into a long? Is it because it can be optimized on various platforms where typedef size_t uint64_t? Or am I missing something? Is there a practical use for a Stream with more than Integer.MAX_VALUE items?

Upvotes: 0

Views: 529

Answers (1)

Sahil Garg
Sahil Garg

Reputation: 167

If the number of elements are more than Integer.MAX value then adding up will wrap on the int max value, which will make total sum value (number of elements) wrong.

We generally write results in long where the result involves addition of elements.

In short, provided long return type to give support for all cases (number of elements less than Integer.MAX and greater than Integer.MAX both).

Upvotes: 3

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