Approach 1: Using mapToInt() and sum()

List<Integer> nums2 = Arrays.asList(5, 6, 7);
int sum = nums2.stream().mapToInt(Integer::intValue).sum();
System.out.println(sum); // 18

Why it works:

• Converts to IntStream and sums elements efficiently.

Approach 2: Using Collectors.summingInt() (Alternative)

int sum = nums2.stream().collect(Collectors.summingInt(Integer::intValue));
System.out.println(sum); // 18

Why it works:

• Collector handles aggregation; useful in complex collector chains.