수집기 및 그룹화

import java.util.*;import java.util.stream.*;public class Main {
  public static void main(String[] args) {
    List<String> names = Arrays.asList("Ada","Bob","Eve");
    List<String> upper = names.stream().map(String::toUpperCase).collect(Collectors.toList());
    System.out.println(upper);
  }
}

import java.util.*;import java.util.stream.*;public class Main {
  public static void main(String[] args) {
    List<String> words = Arrays.asList("Java","is","fun");
    String sentence = words.stream().collect(Collectors.joining(" "));
    System.out.println(sentence);
  }
}

import java.util.*;import java.util.stream.*;public class Main {
  public static void main(String[] args) {
    List<String> names = Arrays.asList("Alice","Bob","Anna");
    Map<Character, List<String>> grouped = names.stream().collect(Collectors.groupingBy(s -> s.charAt(0)));
    System.out.println(grouped);
  }
}