Collectors - Demo3

原创转载请注明出处：http://agilestyle.iteye.com/blog/2425965

 

Outline

testPartitioningByWithPredicate();

testPartitionByWithPredicateAndCollector();

testReducingBinaryOperator();

testReducingBinaryOperatorAndIdentity();

testReducingBinaryOperatorAndIdentityAndFunction();

testSummarizingInt();

testSummarizingLong();

testSummarizingDouble();

 

SRC

package org.fool.java8.collector;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.function.BinaryOperator;
import java.util.stream.Collectors;

public class CollectorsTest3 {

    private 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) {
        testPartitioningByWithPredicate();
        testPartitionByWithPredicateAndCollector();
        testReducingBinaryOperator();
        testReducingBinaryOperatorAndIdentity();
        testReducingBinaryOperatorAndIdentityAndFunction();
        testSummarizingInt();
        testSummarizingLong();
        testSummarizingDouble();
    }

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

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

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

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

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

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

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

    public static class Dish {
        private String name;
        private boolean vegetarian;
        private int calories;
        private Type type;

        public Dish(String name, boolean vegetarian, int calories, Type type) {
            this.name = name;
            this.vegetarian = vegetarian;
            this.calories = calories;
            this.type = type;
        }

        public enum Type { MEAT, FISH, OTHER }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public boolean isVegetarian() {
            return vegetarian;
        }

        public void setVegetarian(boolean vegetarian) {
            this.vegetarian = vegetarian;
        }

        public int getCalories() {
            return calories;
        }

        public void setCalories(int calories) {
            this.calories = calories;
        }

        public Type getType() {
            return type;
        }

        public void setType(Type type) {
            this.type = type;
        }

        @Override
        public String toString() {
            return "Dish{" +
                    "name='" + name + '\'' +
                    ", vegetarian=" + vegetarian +
                    ", calories=" + calories +
                    ", type=" + type +
                    '}';
        }
    }

}

 Console Output

{false=[Dish{name='pork', vegetarian=false, calories=800, type=MEAT}, Dish{name='beef', vegetarian=false, calories=700, type=MEAT}, Dish{name='chicken', vegetarian=false, calories=400, type=MEAT}, Dish{name='prawns', vegetarian=false, calories=300, type=FISH}, Dish{name='salmon', vegetarian=false, calories=450, type=FISH}], true=[Dish{name='french fries', vegetarian=true, calories=530, type=OTHER}, Dish{name='rice', vegetarian=true, calories=350, type=OTHER}, Dish{name='season fruit', vegetarian=true, calories=120, type=OTHER}, Dish{name='pizza', vegetarian=true, calories=550, type=OTHER}]}
{false=530.0, true=387.5}
Dish{name='pork', vegetarian=false, calories=800, type=MEAT}
4200
4200
IntSummaryStatistics{count=9, sum=4200, min=120, average=466.666667, max=800}
LongSummaryStatistics{count=9, sum=4200, min=120, average=466.666667, max=800}
DoubleSummaryStatistics{count=9, sum=4200.000000, min=120.000000, average=466.666667, max=800.000000}