Java8 stream reduce example 2018-06-08 05:32

reduce method of stream is used to calculate elements in the stream and get the result. For example, we can use reduce to get the sum of Integer list. It can also help you to get the min or max number of Integer list.

public class StreamReduceClient {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(6, 5, 8, 9, 63, 36, 83, 85, 86, 96);
        Integer sum =, Integer::sum);
        System.out.println("sum:" + sum);

        Integer max =, Integer::max);
        System.out.println("max:" + max);

        Optional<Integer> min =;
        System.out.println("min:" + min.orElse(-1));

There are two different reduce methods T reduce(T identity, BinaryOperator<T> accumulator) and Optional<T> reduce(BinaryOperator<T> accumulator). The first method will return "identity" if Integer list is empty collection. The second method will produce Optional Object. It means the value maybe is null.

The output of above code.