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stream has already been operated upon の原因と直し方

Streamは1回しか終端操作できません。

 1  import java.util.List;
 2  import java.util.Map;
 3  import java.util.stream.Collectors;
 4  
 5  public class Main {
 6      public static void main(String[] args) {
 7          Map<Integer, String> m = List.of("a", "bb", "cc").stream()
 8              .collect(Collectors.toMap(String::length, s -> s_________________));
                                                                        ^
 9          System.out.println(m);
10      }
11  }