how to sum all elements from arraylist code example

Example 1: inbuild method to sum of an arraylist elements in java

//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();

Example 2: inbuild method to sum of an arraylist elements in java

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