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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.List;
  6. import java.util.function.BiConsumer;
  7. import java.util.function.BinaryOperator;
  8. import java.util.function.Function;
  9. import java.util.function.Supplier;
  10. import java.util.stream.Collector;
  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.         class Intermediate {
  23.             Integer value = null;
  24.             List<MyCustomObject> objects = new ArrayList<>();
  25.         }
  26.         Supplier<Intermediate> supplier = () -> new Intermediate();
  27.         BiConsumer<Intermediate, MyCustomObject> accumulator = (i, c) -> {
  28.             System.out.printf("accumulating %d into %d%n", c.intField, i.value);
  29.             if (i.value != null) {
  30.                 if (c.intField > i.value.intValue()) {
  31.                     // new max found
  32.                     System.out.println("new max " + c.intField + ", dropping " + i.objects.size() + " objects");
  33.                     i.value = c.intField;
  34.                     i.objects.clear();
  35.                 } else if (c.intField < i.value) {
  36.                     return;
  37.                 }
  38.             } else {
  39.                 i.value = c.intField;
  40.             }
  41.             i.objects.add(c);
  42.         };
  43.         BinaryOperator<Intermediate> combiner = (i1, i2) -> {
  44.             System.out.printf("combining %d and %d%n", i1.value, i2.value);
  45.             Intermediate result = new Intermediate();
  46.             result.value = Math.max(i1.value, i2.value);
  47.             if (i1.value.intValue() == result.value.intValue()) {
  48.                 result.objects.addAll(i1.objects);
  49.             }
  50.             if (i2.value.intValue() == result.value.intValue()) {
  51.                 result.objects.addAll(i2.objects);
  52.             }
  53.             return result;
  54.         };
  55.         Function<Intermediate, List<MyCustomObject>> finisher = i -> {
  56.             return i.objects;
  57.         };
  58.         Collector<MyCustomObject, Intermediate, List<MyCustomObject>> collector = Collector.of(supplier, accumulator,
  59.                 combiner, finisher);
  60.         System.out.println(list.stream().collect(collector));
  61.     }
  62.  
  63.     static class MyCustomObject {
  64.         private int intField;
  65.  
  66.         MyCustomObject(int field) {
  67.             intField = field;
  68.         }
  69.  
  70.         public int getIntField() {
  71.             return intField;
  72.         }
  73.  
  74.         @Override
  75.         public String toString() {
  76.             return Integer.toString(intField);
  77.         }
  78.     }
  79. }
  80.  
Success #stdin #stdout 0.16s 33920KB
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stdin
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Standard input is empty
stdout
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accumulating 1 into null
accumulating 9 into 1
new max 9, dropping 1 objects
accumulating 3 into 9
accumulating 7 into 9
accumulating 1 into 9
accumulating 4 into 9
accumulating 5 into 9
accumulating 2 into 9
accumulating 8 into 9
accumulating 5 into 9
accumulating 3 into 9
accumulating 8 into 9
accumulating 0 into 9
accumulating 3 into 9
accumulating 0 into 9
accumulating 9 into 9
accumulating 6 into 9
accumulating 2 into 9
accumulating 6 into 9
accumulating 8 into 9
accumulating 5 into 9
accumulating 6 into 9
accumulating 9 into 9
accumulating 7 into 9
accumulating 1 into 9
accumulating 2 into 9
accumulating 0 into 9
accumulating 4 into 9
accumulating 7 into 9
accumulating 4 into 9
[9, 9, 9]
https://ideone.com/8urTZ7
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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