Stream

요소 반복

public class Test {
    public static void main(String[] args) throws Exception {
        List<String> list = Arrays.asList("A","B","C","D");

        Stream<String> stream = list.stream();

        //람다식에서 파라미터가 하나일때 ()생략 가능.
        stream.forEach(element -> System.out.println(element));
    }
}

String -> Integer배열 반환 후(map이용) 평균값 구하기

public class Test {
    public static void main(String[] args) throws Exception {
        List<String> list = Arrays.asList("30","40","50","60","70");

        double avg = list.stream().mapToInt(e -> Integer.parseInt(e))
                     .average()
                     .getAsDouble();

        System.out.println("평균값 : " + avg);
    }
}

50보다 큰 숫자만 넘는 값만 필터링

public class Test {
    public static void main(String[] args) throws Exception {
        List<Integer> list = Arrays.asList(30,40,50,40,60,70);

        Stream<Integer> stream = list.stream()
                .filter(e -> e > 50);    //

        stream.forEach(e -> System.out.println(e));
    }
}

중복 요소 제거하기

public class Test {
    public static void main(String[] args) throws Exception {
        List<Integer> list = Arrays.asList(30,30,30);

        Stream<Integer> stream = list.stream()
                .distinct();

        stream.forEach(e -> System.out.println(e));
    }
}

오름차순 정렬하기

public class Test {
    public static void main(String[] args) throws Exception {
        List<Integer> list = Arrays.asList(100,90,30,40,50,40,60,70);
        //1
        Stream<Integer> stream = list.stream().sorted();
        //2
        Stream<Integer> stream = list.stream().sorted((a,b) -> a.compareTo(b));

        stream.forEach(e -> System.out.println(e));
    }
}

디폴트처리

public class Test {
    public static void main(String[] args) throws Exception {
        List<Integer> list = Arrays.asList(100,90,30,40,50,40,60,70);

        double a = list.stream()
                .mapToInt(i -> i)
                .filter(i -> i > 100)
                .average()
                .orElse(1000);

        System.out.println(a);    //1000
    }
}