Java 8 Streams - Collectors.summingLong Examples

[Last Updated: Oct 30, 2025]

The static method, Collectors.summingLong() returns a Collector which uses a provided mapper function to convert each input element of type T to primitive long, and returns the sum of the resulting long values.


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

Examples

package com.logicbig.example.collectors;

import java.math.BigDecimal;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class SummingLongExample {
    public static void main (String[] args) {

        Stream<BigDecimal> s = Stream.iterate(
                                         BigDecimal.ONE, bigDecimal ->
                                                bigDecimal.add(BigDecimal.ONE))
                                     .limit(10)
                                     .peek(System.out::println);

        long l = s.collect(Collectors.summingLong(
                            (BigDecimal::longValue)));
        System.out.println("sum: " + l);
    }
}

Output

Original Post

Java 8 Streams - Collectors.summingLong Examples

Examples

Output

See Also