How to Use Reduce Operation with Stream in Java

Reduce is reduction operation in stream . Reduce is use reduce Stream into a single starting with initial value and reduction operation then iteratively combining it with each item of stream using a BinaryOperator  .

Example 

int sum = numberList.stream() .reduce(0,(a,b)->a+b);

Reduce Stream Application 

ReduceStreamApplication.java

package in.jk.java8.stream;

import java.util.Arrays;

import java.util.List;

import java.util.Optional;

public class ReduceStreamApplication {

public static void main(String[] args) {

Integer[] numbers = {1,2,3,4,5,6,7,8,9,10};

List<Integer> numberList =Arrays.asList(numbers);

 

System.out.println("\nReduce With Lambda Expression \n ");

int sum = numberList.stream()

              .reduce(0,(a,b)->a+b);

System.out.println("Sum By Reduce :: "+sum);

 

    System.out.println(" \nReduce With Method Reference \n ");

Optional<Integer> sumOptional = numberList.stream()

                                   .reduce(Integer::sum);

int sum1 =sumOptional.get();

System.out.println("Sum By Reduce :: "+sum1);

}

}

Output in Console ...

 Reduce With Lambda Expression 

 

Sum By Reduce :: 55

 

Reduce With Method Reference 

 

Sum By Reduce :: 55