「方法stream（）未定義的類型設置<Person>」

我想運行一個java程序中找到的java程序，我在java必要的步驟課程中找到。我想使用eclipse來通過它來更好地理解發生了什麼。 Person類沒有錯誤，但是MRTest類最後有一個錯誤，那就是stream（）方法對於調用它的類型是未定義的。我不知道如何解決這個問題。「方法stream（）未定義的類型設置<Person>」

import java.util.List; 
import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.Comparator; 
import java.util.Collection; 
import java.util.function.Supplier; 
import java.util.Set; 
import java.util.HashSet; 
import java.time.chrono.IsoChronology; 

public class MRTest { 

    // The method transferElements copies elements from one collection to 
    // another 

    public static <T, SOURCE extends Collection<T>, DEST extends Collection<T>> 
     DEST transferElements(
      SOURCE sourceCollection, 
      Supplier<DEST> collectionFactory) { 

      DEST result = collectionFactory.get(); 
      for (T t : sourceCollection) { 
       result.add(t); 
      } 
      return result; 
    } 

    public static void main(String... args) { 

     List<Person> roster = Person.createRoster();   

     for (Person p : roster) { 
      p.printPerson(); 
     } 


     Person[] rosterAsArray = 
      roster.toArray(new Person[roster.size()]); 

     class PersonAgeComparator 
      implements Comparator<Person> { 
      public int compare(Person a, Person b) { 
       return a.getBirthday().compareTo(b.getBirthday()); 
      } 
     } 

     // Without method reference 
     Arrays.sort(rosterAsArray, new PersonAgeComparator()); 

     // With lambda expression 
     Arrays.sort(rosterAsArray, 
      (Person a, Person b) -> { 
       return a.getBirthday().compareTo(b.getBirthday()); 
      } 
     ); 

     // With method reference 
     Arrays.sort(rosterAsArray, Person::compareByAge); 

     // Reference to an instance method of a particular object 
     class ComparisonProvider { 
      public int compareByName(Person a, 
       Person b) { 
       return a.getName().compareTo(b.getName()); 
      } 

      public int compareByAge(Person a, 
       Person b) { 
       return a.getBirthday().compareTo(b.getBirthday()); 
      } 
     } 
     ComparisonProvider myComparisonProvider = new ComparisonProvider(); 
     Arrays.sort(rosterAsArray, myComparisonProvider::compareByName); 

     // Reference to an instance method 
     // of an arbitrary object of a particular type 

     String[] stringArray = { "Barbara", "James", "Mary", "John", 
      "Patricia", "Robert", "Michael", "Linda" }; 
     Arrays.sort(stringArray, String::compareToIgnoreCase); 

     Set<Person> rosterSetLambda = 
      transferElements(roster,() -> { return new HashSet<>(); }); 

     Set<Person> rosterSet = transferElements(
      roster, HashSet::new); 
     System.out.println("Printing rosterSet:"); 
     rosterSet.stream().forEach(p -> p.printPerson()); // This is the line that is the problem. 
    } 
}

來源

2014-07-10 Jpaji Rajnish

什麼Java編譯器是你使用Eclipse？ –

你有什麼版本的Java JDK？流被添加到8，所以你可能有一箇舊版本。 – resueman

eclipse luna 4.4，JRE8和java兼容級別1.8 –

問題是你在你的類路徑中有1.7 SE庫，將其更改爲1.8固定它

_{參見細節問題評論部分}

來源

2014-07-11 00:07:31

「方法stream（）未定義的類型設置<Person>」

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