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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.util.stream.*;
  5. import java.lang.*;
  6. import java.io.*;
  7.  
  8. /* Name of the class has to be "Main" only if the class is public. */
  9. class Ideone
  10. {
  11.     static class MyObject {
  12.         private String key;
  13.         private String value1;
  14.         private String value2;
  15.  
  16.         MyObject(String key, String value1, String value2) {
  17.             this.key = key;
  18.             this.value1 = value1;
  19.             this.value2 = value2;
  20.         }
  21.     }
  22.  
  23.     static class MyCreatedObject {
  24.         private String key;
  25.         private List<String> value1List = new ArrayList<>();
  26.         private List<String> value2List = new ArrayList<>();
  27.  
  28.         static Collector<MyObject, ?, MyCreatedObject> collector() {
  29.             return Collector.of(MyCreatedObject::new, MyCreatedObject::add, MyCreatedObject::merge);
  30.         }
  31.  
  32.         void add(MyObject o) {
  33.             key = o.key;
  34.             value1List.add(o.value1);
  35.             value2List.add(o.value2);
  36.         }
  37.  
  38.         MyCreatedObject merge(MyCreatedObject other) {
  39.             key = other.key;
  40.             value1List.addAll(other.value1List);
  41.             value2List.addAll(other.value2List);
  42.             return this;
  43.         }
  44.  
  45.         @Override
  46.         public String toString() {
  47.             return String.format("{key=%s, value1List=%s, value2List=%s}",
  48.                     key, value1List, value2List);
  49.         }
  50.     }
  51.  
  52.     public static void main(String[] args) {
  53.         List<MyObject> list = Arrays.asList(
  54.                 new MyObject("1", "WWW", "EEE"),
  55.                 new MyObject("1", "WWW", "AAA"),
  56.                 new MyObject("2", "WWW", "EEE"));
  57.  
  58.         Map<String, MyCreatedObject> grouped = list.stream()
  59.                 .collect(Collectors.groupingBy(o -> o.key, MyCreatedObject.collector()));
  60.  
  61.         System.out.println(grouped.values());
  62.     }
  63. }
Success #stdin #stdout 0.09s 48800KB
comments ()
stdin 
Standard input is empty
stdout 
[{key=1, value1List=[WWW, WWW], value2List=[EEE, AAA]}, {key=2, value1List=[WWW], value2List=[EEE]}]
https://ideone.com/kRUrGr
language:
Java (HotSpot 12)
created:
3 years ago
visibility:
public

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