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  1. import java.util.Arrays;
  2. import java.util.Objects;
  3. import java.util.function.BinaryOperator;
  4. import java.util.function.Function;
  5. import java.util.function.Predicate;
  6. import java.util.stream.Stream;
  7.  
  8. class PredicateExample {
  9.   public static void main(String[] args) {
  10.     Stream<Animal> greenAnimals = Stream.<Animal>of()
  11.         .filter(
  12.             MultiPred.ofOr(Animal::getColor, Color.WHITE::equals, Color.GREEN::equals)
  13.                 .or(
  14.                     MultiPred.of(Animal::getType, AnimalType.CARNIVORE::equals)
  15.                     .and(Animal::canFly) // we can chain custom Predicates with regular ones
  16.                 )
  17.                 .or(
  18.                     MultiPred.of(Animal::getType, AnimalType.HERBIVORE::equals)
  19.                     .and(MultiPred.of(Animal::getColor, Color.PURPLE::equals)
  20.                         .or(Animal::canSwim)
  21.                     )
  22.                 )
  23.         );
  24.     System.out.println("No errors");
  25.   }
  26. }
  27. class MultiPred {
  28.   @SafeVarargs
  29.   public static <T, K> Predicate<T> ofAnd(Function<T, K> keyExtractor,
  30.                                              Predicate<K>... predicates) {
  31.  
  32.       return of(keyExtractor, k -> true, Predicate::and, predicates);
  33.   }
  34.  
  35.   @SafeVarargs
  36.   public static <T, K> Predicate<T> ofOr(Function<T, K> keyExtractor,
  37.                                             Predicate<K>... predicates) {
  38.  
  39.       return of(keyExtractor, k -> false, Predicate::or, predicates);
  40.   }
  41.  
  42.   @SafeVarargs
  43.   public static <T, K> Predicate<T> of(Function<T, K> keyExtractor,
  44.                                           Predicate<K> identity,
  45.                                           BinaryOperator<Predicate<K>> op,
  46.                                           Predicate<K>... predicates) {
  47.  
  48.       Objects.requireNonNull(predicates);
  49.  
  50.       Predicate<K> predicate = Arrays.stream(predicates).reduce(identity, op);
  51.  
  52.       return of(keyExtractor, predicate);
  53.   }
  54.  
  55.   public static <T, K> Predicate<T> of(Function<T, K> keyExtractor,
  56.                                           Predicate<K> predicate) {
  57.  
  58.       Objects.requireNonNull(keyExtractor);
  59.       Objects.requireNonNull(predicate);
  60.  
  61.       return t -> predicate.test(keyExtractor.apply(t));
  62.   }
  63. }
  64. enum Color { WHITE, GREEN, PURPLE }
  65. enum AnimalType { HERBIVORE, CARNIVORE }
  66. class Animal {
  67.   final AnimalType type;
  68.   final Color color;
  69.   final boolean canSwim, canFly;
  70.  
  71.   Animal(AnimalType type, Color color, boolean canSwim, boolean canFly) {
  72.     this.type = type;
  73.     this.color = color;
  74.     this.canSwim = canSwim;
  75.     this.canFly = canFly;
  76.   }
  77.   public AnimalType getType() { return type; }
  78.   public Color getColor() { return color; }
  79.   public boolean canSwim() { return canSwim; }
  80.   public boolean canFly() { return canFly; }
  81. }
  82.  
Success #stdin #stdout 0.11s 48488KB
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https://ideone.com/6sNBP3
language:
Java (HotSpot 12)
created:
1 year ago
visibility:
secret

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