Java Streams - Collectors summingDouble (ToDoubleFunction mapper)

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

Syntax

summingDouble has the following syntax.

public static <T> Collector<T,?,Double> summingDouble(ToDoubleFunction<? super T> mapper)

Example

The following example shows how to use summingDouble.

import java.util.stream.Collectors;
import java.util.stream.Stream;
/*from  www  . ja  v  a 2s . c o m*/
public class Main {
  public static void main(String[] args) {
    Stream<String> s = Stream.of("1","2","3");
    
    double o =  s.collect(Collectors.summingDouble(n->Double.parseDouble(n)));

    System.out.println(o);
  }
}

The code above generates the following result.

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