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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Collections;
  5. import java.util.Comparator;
  6. import java.util.List;
  7. import java.util.Optional;
  8. import java.util.function.BinaryOperator;
  9. import java.util.stream.Collector;
  10. import java.util.stream.Stream;
  11.  
  12. public class Main {
  13.     public static void main(String[] args) {
  14.         ArrayList<MyCustomObject> list = new ArrayList<>();
  15.         for (int i = 0; i < 10; i++) {
  16.             for (int j = 0; j < 3; j++) {
  17.                 list.add(new MyCustomObject(i));
  18.             }
  19.         }
  20.         Collections.shuffle(list);
  21.  
  22.         Comparator<MyCustomObject> compare = Comparator.comparing(MyCustomObject::getIntField);
  23.         class Intermediate {
  24.             MyCustomObject value = null;
  25.             List<MyCustomObject> objects = new ArrayList<>();
  26.  
  27.             void add(MyCustomObject c) {
  28.                 if (objects.isEmpty()) {
  29.                     value = c;
  30.                 } else {
  31.                     int compareResult = compare.compare(c, objects.get(0));
  32.                     if (compareResult > 0) {
  33.                         // new max found
  34.                         System.out.println("new max " + c.intField + ", dropping " + objects.size() + " objects");
  35.                         value = c;
  36.                         objects.clear();
  37.                     } else if (compareResult < 0) {
  38.                         return;
  39.                     }
  40.                 }
  41.                 objects.add(c);
  42.             }
  43.         }
  44.         BinaryOperator<Intermediate> combiner = (i1, i2) -> {
  45.             System.out.printf("combining %d and %d%n", i1.value, i2.value);
  46.             Intermediate result = new Intermediate();
  47.             Optional<MyCustomObject> max = Stream.of(i1, i2).filter(i -> !i.objects.isEmpty())
  48.                     .map(i -> i.objects.get(0)).max(compare);
  49.             max.ifPresent(m -> {
  50.                 if (compare.compare(i1.value, m) == 0) {
  51.                     result.objects.addAll(i1.objects);
  52.                 }
  53.                 if (compare.compare(i2.value, m) == 0) {
  54.                     result.objects.addAll(i2.objects);
  55.                 }
  56.             });
  57.             return result;
  58.         };
  59.         Collector<MyCustomObject, Intermediate, List<MyCustomObject>> collector = Collector.of(Intermediate::new,
  60.                 Intermediate::add, combiner, i -> i.objects);
  61.         System.out.println(list.stream().collect(collector));
  62.     }
  63.  
  64.     static class MyCustomObject {
  65.         private int intField;
  66.  
  67.         MyCustomObject(int field) {
  68.             intField = field;
  69.         }
  70.  
  71.         public int getIntField() {
  72.             return intField;
  73.         }
  74.  
  75.         @Override
  76.         public String toString() {
  77.             return Integer.toString(intField);
  78.         }
  79.     }
  80. }
  81.  
Success #stdin #stdout 0.22s 34032KB
comments (?)
stdin 
Standard input is empty
stdout 
new max 3, dropping 1 objects
new max 7, dropping 1 objects
new max 9, dropping 3 objects
[9, 9, 9]
https://ideone.com/H3lQy7
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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