Java 8 – 收集器Collectors_实战

public class CollectorsAction { 

public  static List<Dish> menu = Arrays.asList(
new Dish("pork", false, 800, Dish.Type.MEAT),
new Dish("beef", false, 700, Dish.Type.MEAT),
new Dish("chicken", false, 400, Dish.Type.MEAT),
new Dish("french fries", true, 530, Dish.Type.OTHER),
new Dish("rice", true, 350, Dish.Type.OTHER),
new Dish("season fruit", true, 120, Dish.Type.OTHER),
new Dish("pizza", true, 550, Dish.Type.OTHER),
new Dish("prawns", false, 300, Dish.Type.FISH),
new Dish("salmon", false, 450, Dish.Type.FISH));
public static void main(String[] args) { 

testAveragingDouble();
testAveragingInt();
testAveragingLong();
testCollectingAndThen();
testCounting();
testGroupingByFunction();
testGroupingByFunctionAndCollector();
testGroupingByFunctionAndSupplierAndCollector();
testSummarizingInt();
testGroupingByConcurrentWithFunction();
testGroupingByConcurrentWithFunctionAndCollector();
testGroupingByConcurrentWithFunctionAndSupplierAndCollector();
testJoining();
testJoiningWithDelimiter();
testJoiningWithDelimiterAndPrefixAndSuffix();
testMapping();
testMaxBy();
testMinBy();
testPartitioningByWithPredicate();
testPartitioningByWithPredicateAndCollector();
testReducingBinaryOperator();
testReducingBinaryOperatorAndIdentiy();
testReducingBinaryOperatorAndIdentiyAndFunction();
testSummarizingDouble();
testSummarizingLong();
testSummarizingInt();
}
private static void testAveragingDouble() { 

System.out.println("testAveragingDouble");
Optional.ofNullable(menu.stream().collect(Collectors.averagingDouble(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testAveragingInt() { 

System.out.println("testAveragingInt");
Optional.ofNullable(menu.stream().collect(Collectors.averagingInt(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testAveragingLong() { 

System.out.println("testAveragingLong");
Optional.ofNullable(menu.stream().collect(Collectors.averagingLong(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testCollectingAndThen() { 

System.out.println("testCollectingAndThen");
Optional.ofNullable(menu.stream().collect(Collectors.collectingAndThen(Collectors.averagingInt(Dish::getCalories), a -> "The Average Calories is->" + a)))
.ifPresent(System.out::println);
/* List<Dish> list = menu.stream().filter(d -> d.getType().equals(Dish.Type.MEAT)) .collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)); list.add(new Dish("", false, 100, Dish.Type.OTHER)); System.out.println(list);*/
}
private static void testCounting() { 

System.out.println("testCounting");
Optional.of(menu.stream().collect(Collectors.counting())).ifPresent(System.out::println);
}
private static void testGroupingByFunction() { 

System.out.println("testGroupingByFunction");
Optional.of(menu.stream().collect(Collectors.groupingBy(Dish::getType)))
.ifPresent(System.out::println);
}
private static void testGroupingByFunctionAndCollector() { 

System.out.println("testGroupingByFunctionAndCollector");
Optional.of(menu.stream().collect(Collectors.groupingBy(Dish::getType, Collectors.averagingInt(Dish::getCalories))))
.ifPresent(System.out::println);
}
private static void testGroupingByFunctionAndSupplierAndCollector() { 

System.out.println("testGroupingByFunctionAndSupplierAndCollector");
Map<Dish.Type, Double> map = menu.stream().collect(Collectors.groupingBy(Dish::getType, TreeMap::new, Collectors.averagingInt(Dish::getCalories)));
Optional.of(map.getClass()).ifPresent(System.out::println);
Optional.of(map).ifPresent(System.out::println);
}
private static void testSummarizingInt() { 

System.out.println("testSummarizingInt");
IntSummaryStatistics result = menu.stream().collect(Collectors.summarizingInt(Dish::getCalories));
Optional.of(result).ifPresent(System.out::println);
}
private static void testGroupingByConcurrentWithFunction() { 

System.out.println("testGroupingByConcurrentWithFunction");
ConcurrentMap<Dish.Type, List<Dish>> collect = menu.stream().collect(Collectors.groupingByConcurrent(Dish::getType));
Optional.ofNullable(collect.getClass()).ifPresent(System.out::println);
Optional.ofNullable(collect).ifPresent(System.out::println);
}
private static void testGroupingByConcurrentWithFunctionAndCollector() { 

System.out.println("testGroupingByConcurrentWithFunctionAndCollector");
ConcurrentMap<Dish.Type, Double> collect = menu.stream()
.collect(Collectors.groupingByConcurrent(Dish::getType, Collectors.averagingInt(Dish::getCalories)));
Optional.ofNullable(collect).ifPresent(System.out::println);
}
private static void testGroupingByConcurrentWithFunctionAndSupplierAndCollector() { 

System.out.println("testGroupingByConcurrentWithFunctionAndSupplierAndCollector");
ConcurrentMap<Dish.Type, Double> collect = menu.stream()
.collect(Collectors.groupingByConcurrent(Dish::getType, ConcurrentSkipListMap::new, Collectors.averagingInt(Dish::getCalories)));
Optional.of(collect.getClass()).ifPresent(System.out::println);
Optional.ofNullable(collect).ifPresent(System.out::println);
}
private static void testJoining() { 

System.out.println("testJoining");
Optional.of(menu.stream().map(Dish::getName).collect(Collectors.joining()))
.ifPresent(System.out::println);
}
private static void testJoiningWithDelimiter() { 

System.out.println("testJoiningWithDelimiter");
Optional.of(menu.stream().map(Dish::getName).collect(Collectors.joining(",")))
.ifPresent(System.out::println);
}
private static void testJoiningWithDelimiterAndPrefixAndSuffix() { 

System.out.println("testJoiningWithDelimiterAndPrefixAndSuffix");
Optional.of(menu.stream().map(Dish::getName).collect(Collectors.joining(",", "Names[", "]")))
.ifPresent(System.out::println);
}
private static void testMapping() { 

System.out.println("testMapping");
Optional.of(menu.stream().collect(Collectors.mapping(Dish::getName, Collectors.joining(","))))
.ifPresent(System.out::println);
}
private static void testMaxBy() { 

System.out.println("testMaxBy");
menu.stream().collect(Collectors.maxBy(Comparator.comparingInt(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testMinBy() { 

System.out.println("testMinBy");
menu.stream().collect(Collectors.minBy(Comparator.comparingInt(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testPartitioningByWithPredicate() { 

System.out.println("testPartitioningByWithPredicate");
Map<Boolean, List<Dish>> collect = menu.stream().collect(Collectors.partitioningBy(Dish::isVegetarian));
Optional.of(collect).ifPresent(System.out::println);
}
private static void testPartitioningByWithPredicateAndCollector() { 

System.out.println("testPartitioningByWithPredicateAndCollector");
Map<Boolean, Double> collect = menu.stream()
.collect(Collectors.partitioningBy(Dish::isVegetarian, Collectors.averagingInt(Dish::getCalories)));
Optional.of(collect).ifPresent(System.out::println);
}
private static void testReducingBinaryOperator() { 

System.out.println("testReducingBinaryOperator");
menu.stream().collect(
Collectors.reducing(
BinaryOperator.maxBy(
Comparator.comparingInt(Dish::getCalories)
)
)
).ifPresent(System.out::println);
}
private static void testReducingBinaryOperatorAndIdentiy() { 

System.out.println("testReducingBinaryOperatorAndIdentiy");
Integer result = menu.stream()
.map(Dish::getCalories).collect(Collectors.reducing(0, (d1, d2) -> d1 + d2));
System.out.println(result);
}
private static void testReducingBinaryOperatorAndIdentiyAndFunction() { 

System.out.println("testReducingBinaryOperatorAndIdentiyAndFunction");
Integer result = menu.stream().collect(Collectors.reducing(0, Dish::getCalories, (d1, d2) -> d1 + d2));
System.out.println(result);
}
private static void testSummarizingDouble() { 

System.out.println("testSummarizingDouble");
Optional.of(menu.stream().collect(Collectors.summarizingDouble(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testSummarizingLong() { 

System.out.println("testSummarizingLong");
Optional.of(menu.stream().collect(Collectors.summarizingLong(Dish::getCalories)))
.ifPresent(System.out::println);
}
private static void testSummarizingInt() { 

System.out.println("testSummarizingLong");
Optional.of(menu.stream().collect(Collectors.summarizingInt(Dish::getCalories)))
.ifPresent(System.out::println);
}
}