Is there possibility of sum of ArrayList without looping

Question

Is there possibility of sum of ArrayList without looping?

PHP provides sum(array) which will give the sum of array.

The PHP code is

Answer 1

Given that a list can hold any type of object, there is no built in method which allows you to sum all the elements. You could do something like this:

int sum = 0;

for( Integer i : ( ArrayList<Integer> )tt ) {
  sum += i;
}

Alternatively you could create your own container type which inherits from ArrayList but also implements a method called sum() which implements the code above.

Answer 2

Write a util function like

public class ListUtil{

    public static int sum(List<Integer> list){
      if(list==null || list.size()<1)
        return 0;

      int sum = 0;
      for(Integer i: list)
        sum = sum+i;

      return sum;
    }
}

Then use like

int sum = ListUtil.sum(yourArrayList)

Answer 3

This link shows three different ways how to sum in java, there is one option that is not in previous answers using Apache Commons Math..

Example:

public static void main(String args []){
    List<Double> NUMBERS_FOR_SUM = new ArrayList<Double>(){
         {
            add(5D);
            add(3.2D);
            add(7D);
         }
    };
    double[] arrayToSume = ArrayUtils.toPrimitive(NUMBERS_FOR_SUM
            .toArray(new Double[NUMBERS_FOR_SUM.size()]));    
    System.out.println(StatUtils.sum(arrayToSume));

}

See StatUtils api

Answer 4

ArrayList is a Collection of elements (in the form of list), primitive are stored as wrapper class object but at the same time i can store objects of String class as well. SUM will not make sense in that. BTW why are so afraid to use for loop (enhanced or through iterator) anyways?

Answer 5

This can be done with reduce using method references reduce(Integer::sum):

Integer reduceSum = Arrays.asList(1, 3, 4, 6, 4)
        .stream()
        .reduce(Integer::sum)
        .get();

Or without Optional:

Integer reduceSum = Arrays.asList(1, 3, 4, 6, 4)
        .stream()
        .reduce(0, Integer::sum);

Answer 6

for me the clearest way is this:

doubleList.stream().reduce((a,b)->a+b).get();

or

doubleList.parallelStream().reduce((a,b)->a+b).get();

It also use internal loops, but it is not possible without loops.