What is the Java equivalent to Python's reduce function?

Question

Similar questions have been asked, here and here, but given the advent of Java 8, and the generally outdated nature of these questions I'm wondering if now there'd be something at least kindred to it?

This is what I'm referring to.

Answer 1

You can use a lambda and Stream.reduce, there is a page in the docs dedicated to reductions:

Integer totalAgeReduce = roster
   .stream()
   .map(Person::getAge)
   .reduce(
       0,
       (a, b) -> a + b);

Answer 2

This is the example used in the Python docs implemented with Java 8 streams:

List<Integer> numbers = Arrays.asList(new Integer[] { 1, 2, 3, 4, 5 });
Optional<Integer> sum = numbers.stream().reduce((a, b) -> a + b);
System.out.println(sum.get());