Is there possibility of sum of ArrayList without looping

Is there possibility of sum of ArrayList without looping?

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

The PHP code is like

$a = array(2, 4, 6, 8);
echo "sum(a) = " . array_sum($a) . "\n";

I wanted to do the same in Java:

List tt = new ArrayList();
tt.add(1);
tt.add(2);
tt.add(3);

Solution 1:

Once java-8 is out (March 2014) you'll be able to use streams:

If you have a List<Integer>

int sum = list.stream().mapToInt(Integer::intValue).sum();

If it's an int[]

int sum = IntStream.of(a).sum();

Solution 2:

Then write it yourself:

public int sum(List<Integer> list) {
     int sum = 0; 

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

     return sum;
}

Solution 3:

The only alternative to using a loop is to use recursion.

You can define a method like

public static int sum(List<Integer> ints) {
   return ints.isEmpty() ? 0 : ints.get(0) + ints.subList(1, ints.length());
}

This is very inefficient compared to using a plain loop and can blow up if you have many elements in the list.

An alternative which avoid a stack overflow is to use.

public static int sum(List<Integer> ints) {
    int len = ints.size();
    if (len == 0) return 0;
    if (len == 1) return ints.get(0);
    return sum(ints.subList(0, len/2)) + sum(ints.subList(len/2, len));
}

This is just as inefficient, but will avoid a stack overflow.

The shortest way to write the same thing is

int sum = 0, a[] = {2, 4, 6, 8};

for(int i: a) {
    sum += i;
}

System.out.println("sum(a) = " + sum);

prints

sum(a) = 20

Solution 4:

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)