归约和汇总

package com.ant.jdk8.chap06;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class MaxByMinByDemo {
    public static void main(String[] args) {
        List<Dish> menu = Arrays.asList(
                new Dish("pork", false, 800, Type.MEAT),
                new Dish("beef", false, 700, Type.MEAT),
                new Dish("chicken", false, 400, Type.MEAT),
                new Dish("french fries", true, 530, Type.OTHER),
                new Dish("rice", true, 350, Type.OTHER),
                new Dish("season fruit", true, 120, Type.OTHER),
                new Dish("pizza", true, 550, Type.OTHER),
                new Dish("prawns", false, 300, Type.FISH),
                new Dish("salmon", false, 450, Type.FISH) );
        menu.stream()
                .collect(Collectors.maxBy(Comparator.comparingInt(Dish::getCalories)))
                .ifPresent(d-> System.out.println(d.getCalories()+"->"+d.getName()));
    }
}

int totalCalories = menu.stream().collect(Collectors.summingInt(Dish::getCalories));
System.out.println("totalCalories:"+totalCalories);

IntSummaryStatistics menuStatistics = menu.stream().collect(Collectors.summarizingInt(Dish::getCalories));
System.out.println(menuStatistics);

String menuStr = menu.stream().map(Dish::getName).collect(Collectors.joining(", "));
System.out.println(menuStr);

int totalCalories1 = menu.stream().collect(Collectors.reducing(0,Dish::getCalories,Integer::sum));
int totalCalories2 = menu.stream().map(Dish::getCalories).reduce(Integer::sum).get();
int totalCalories3 = menu.stream().mapToInt(Dish::getCalories).sum();
System.out.println(totalCalories1+","+totalCalories2+","+totalCalories3);