How to calculate the sum of numbers in list asynchronously?

We will be using ExecutorService from Executor framework and Future interface to make asynchronous calls.

We will be using Streams from Java 8 to calculate the sum of integers in the list.

import java.util.List;
import java.util.concurrent.Callable;
import java.util.stream.Collectors;

public class SumCalculator implements Callable {

    List inputList;

    public SumCalculator(List inputList){
        this.inputList = inputList;
    }

    @Override
    public Integer call() throws Exception {
        return inputList.stream().collect(Collectors.summingInt(i->i));
    }
}

Let’s split the list to 2 sublist and pass them to two different threads so that the sum is calculated asynchronously and returned.

We will use future.get() to get the result from each thread and combine to get the final total.

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Future;

import java.util.stream.IntStream;



public class ListSumAsync {



    public static void main(String...args){

        ExecutorService executorService =

                Executors.newFixedThreadPool(2);



        List intList = new ArrayList<>();

        //Let us add 0 to 100 to a list

        IntStream.range(1, 11)

                .forEach(i -> intList.add(i));



        //Let's split the list to 2 lists and pass

        // it to two threads and combine the result

        SumCalculator calculator1 =

                new SumCalculator(intList.

                        subList(0,intList.size()/2));

        Future result1 =

                executorService.submit(calculator1);



        SumCalculator calculator2 =

                new SumCalculator(intList.subList(

                        (intList.size()/2),intList.size()));

        Future result2 =

                executorService.submit(calculator2);



        try {

            int total = result1.get().intValue()+

                    result2.get().intValue();

            System.out.println("Total sum: "+total);

        } catch (InterruptedException e) {

            e.printStackTrace();

        } catch (ExecutionException e) {

            e.printStackTrace();

        }

    }



}

Also see How to combine results of two threads in java?

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