[section 1] Java 심화(3) - 스트림 코플릿

스트림 코플릿 연습문제

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
    
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);

        // sum
        System.out.println(list.stream().mapToInt(n -> n).sum());   // 15
        System.out.println(list.stream().mapToInt(n -> n).average().getAsDouble()); // 3.0
        // filter, collect, count
        System.out.println(list.stream().filter(n -> n % 2 == 0).collect(Collectors.toList()));    // [2, 4]
        System.out.println(list.stream().filter(n -> n % 2 == 0).count());  // 2
        // map
        System.out.println(list.stream().map(n -> n * 2).collect(Collectors.toList())); // [2, 4, 6, 8, 10]


        List<String> names = Arrays.asList("kim", "hong", "choi", "kim", "lee");

        // distinct, sorted
        System.out.println(names.stream().distinct().sorted().collect(Collectors.toList()));    // [choi, hong, kim, lee]
        // filter(startWith)
        System.out.println(names.stream().filter(n -> n.startsWith("k")).sorted().collect(Collectors.toList()));    // [choi, hong, kim, lee]


        
        List<String> list1 = Arrays.asList("Hello");
        List<String> list2 = Arrays.asList("World");

        // concat
        System.out.println(Stream.concat(list1.stream(), list2.stream()).collect(Collectors.toList())); // [Hello, World]




    }
}