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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.Arrays;
  4. import java.util.List;
  5. import java.util.Map;
  6. import java.util.concurrent.ConcurrentHashMap;
  7. import java.util.function.Function;
  8. import java.util.function.Predicate;
  9. import static java.util.stream.Collectors.toList;
  10.  
  11. /* Name of the class has to be "Main" only if the class is public. */
  12. class Ideone
  13. {
  14.  
  15.     public static void main(String[] args) {
  16.         List<Person> listPersons = Arrays.asList(
  17.                 new Person(1, "person1"),
  18.                 new Person(1, "person5"),
  19.                 new Person(2, "person2"),
  20.                 new Person(1, "person1"),
  21.                 new Person(1, "person2"),
  22.                 new Person(1, "person1"),
  23.                 new Person(3, "person3")
  24.         );
  25.         List<Person> persons = listPersons.stream()
  26.                 .filter(distinctByKey(pr -> pr.getId() + " " + pr.getName()))
  27.                 .collect(toList());
  28.  
  29.         persons.forEach(System.out::println);
  30.     }
  31.  
  32.     private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
  33.         Map<Object, Boolean> seen = new ConcurrentHashMap<>();
  34.         return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
  35.     }
  36.  
  37. }
  38.  
  39. class Person {
  40.  
  41.     private int id;
  42.     private String name;
  43.  
  44.     public Person() {
  45.     }
  46.  
  47.     public int getId() {
  48.         return id;
  49.     }
  50.  
  51.     public Person(int id, String name) {
  52.         this.id = id;
  53.         this.name = name;
  54.     }
  55.  
  56.     public String getName() {
  57.         return name;
  58.     }
  59.  
  60.     public void setName(String name) {
  61.         this.name = name;
  62.     }
  63.  
  64.     @Override
  65.     public String toString() {
  66.         return "Person{" + "id=" + id + ", name=" + name + '}';
  67.     }
  68.  
  69. }
Success #stdin #stdout 0.24s 33840KB
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stdin
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Standard input is empty
stdout
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Person{id=1, name=person1}
Person{id=1, name=person5}
Person{id=2, name=person2}
Person{id=1, name=person2}
Person{id=3, name=person3}
https://ideone.com/B5q8NH
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
public

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