import java.util.stream.*;

​

public class prog {

    public static void main(String[] args){

        Stream<String> stream1 = Stream.of("넷", "둘", "셋", "하나");

        Stream<String> stream2 = Stream.of("넷", "둘", "셋", "하나");

        Optional<String> result1 = stream1.reduce((s1, s2) -> s1 + "++" + s2);

        result1.ifPresent(System.out::println);

        String result2 = stream2.reduce("시작", (s1, s2) -> s1 + "++" + s2);

        System.out.println(result2);

    }

}