java中reduce在流的使用

Optional<T> reduce(BinaryOperator<T> accumulator);

T reduce(T identity, BinaryOperator<T> accumulator);

 <U> U reduce(U identity,

                 BiFunction<U, ? super T, U> accumulator,

                 BinaryOperator<U> combiner);

Optional<String> reduced =

    stringCollection

        .stream()

        .sorted()

        .reduce((s1, s2) -> s1 + "#" + s2);

reduced.ifPresent(System.out::println);

// "aaa1#aaa2#bbb1#bbb2#bbb3#ccc#ddd1#ddd2"