Java 8: Sum and aggregate with Stream.reduce

reduce folds a stream into a single value using an identity and an accumulator.

Code

List<Integer> nums = List.of(2, 4, 6, 8);
int sum = nums.stream().reduce(0, Integer::sum);
int product = nums.stream().reduce(1, (a, b) -> a * b);
System.out.println("sum=" + sum + " product=" + product);

Output

sum=20 product=384

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Published 2026-07-26