Java Streams - Collectors summingLong(ToLongFunction mapper) example

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Collectors summingLong(ToLongFunction<? super T> mapper) returns a Collector that produces the sum of a long-valued function applied to the input elements.

Syntax

summingLong has the following syntax.

public static <T> Collector<T,?,Long> summingLong(ToLongFunction<? super T> mapper)

Example

The following example shows how to use summingLong.

import java.util.stream.Collectors;
import java.util.stream.Stream;
/*from  ww w.ja va2  s .  com*/
public class Main {
  public static void main(String[] args) {
    Stream<String> s = Stream.of("1","2","3");
    
    long o =  s.collect(Collectors.summingLong(n->Long.parseLong(n)));

    System.out.println(o);
  }
}

The code above generates the following result.

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