Java Streams - Stream reduce(BinaryOperator accumulator) example

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Stream reduce(BinaryOperator<T> accumulator) performs a reduction on the elements of this stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any.

Syntax

reduce has the following syntax.

Optional<T> reduce(BinaryOperator<T> accumulator)

Example

The following example shows how to use reduce.

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
//w  w  w  .  j  a v a  2s  . c o  m
public class Main {
  public static void main(String[] args) {
    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
    Optional<Integer> sum = numbers.stream()
                     .reduce(Integer::sum);
    if(sum.isPresent()){
      System.out.println(sum.get());
    }else{
      System.out.println("noValue ");  
    }
    
  }
}

The code above generates the following result.

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