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

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

You can define a method like

public static int sum(List 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 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